Adapted to typesetter and added a reference for LLgen.
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ceriel
parent
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1 changed files with 101 additions and 33 deletions
134
doc/top/top.n
134
doc/top/top.n
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@ -1,8 +1,4 @@
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.ND
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.pl 11.7i
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.ll 80m
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.nr LL 80m
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.nr tl 78m
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.tr ~
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.ds >. .
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.TL
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@ -82,6 +78,7 @@ machine-dependent description table (see figure 1.).
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So the major part of the code of a target optimizer is
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shared among all target optimizers.
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.DS
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.ft 5
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|-------------------------|
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@ -95,6 +92,7 @@ table | | | |
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|-----------------| |-------------------------|
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target optimizer
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.ft R
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Figure 1: Generation of a target optimizer.
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@ -163,22 +161,26 @@ ANY matches every instruction mnemonic.
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.nf
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Examples of mnemonic descriptions:
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.ft 5
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add
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sub.l
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mulw3
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ANY
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.ft R
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.fi
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.PP
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An operand can also be described by a string constant.
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.nf
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Examples:
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.ft 5
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(sp)+
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r5
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-4(r6)
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.ft R
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.fi
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Alternatively, it can be described by means of a \fIvariable name\fR.
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Variables have values which are strings.
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@ -187,22 +189,27 @@ Each such declaration defines the name of a variable and
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a \fIrestriction\fR to which its value is subjected.
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.nf
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Example of variable declarations:
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.ft 5
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CONST { VAL[0] == '$' };
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REG { VAL[0] == 'r' && VAL[1] >= '0' && VAL[1] <= '3' &&
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VAL[2] == '\\0' };
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X { TRUE };
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.ft R
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.fi
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The keyword VAL denotes the value of the variable, which is
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a null-terminated string.
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An operand description given via a variable name matches an
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actual operand if the actual operand obeys the associated restriction.
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.nf
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.ft 5
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CONST matches $1, $-5, $foo etc.
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REG matches r0, r1, r2 and r3
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X matches anything
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.ft R
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.fi
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The restriction (between curly braces) may be any legal "C"
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.[
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@ -214,9 +221,11 @@ These procedures must be added to the table after the patterns.
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.nf
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Example:
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.ft 5
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FERMAT_NUMBER { VAL[0] == '$' && is_fermat_number(&VAL[1]) };
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.ft R
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.fi
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An operand can also be described by a mixture of a string constant
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and a variable name.
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@ -226,9 +235,11 @@ The most general form allowed is:
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string_constant1 variable_name string_constant2
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Example:
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.ft 5
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(REG)+ matches (r0)+, (r1)+, (r2)+ and (r3)+
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.ft R
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.fi
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Any of the three components may be omitted,
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so the first two forms are just special cases of the general form.
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@ -254,17 +265,23 @@ the optional constraint C is satisfied, i.e. it evaluates to TRUE.
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.LP
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.nf
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The pattern:
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.ft 5
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dec REG : move.b CONST,(REG)
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.ft R
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matches:
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.ft 5
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dec r0 : move.b $4,(r0)
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.ft R
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but not:
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.ft 5
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dec r0 : move.b $4,(r1)
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.ft R
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(as the variable REG matches two different strings).
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.fi
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If a pattern containing different registers must be described,
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@ -272,10 +289,12 @@ extra names for a register should be declared, all sharing
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the same restriction.
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.nf
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Example:
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.ft 5
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REG1,REG2 { VAL[0] == 'r' && ..... };
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addl3 REG1,REG1,REG2 : subl2 REG2,REG1
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.ft R
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.fi
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.PP
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The optional constraint is an auxiliary "C" expression (just like
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@ -283,14 +302,18 @@ the parameter restrictions).
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The expression may refer to the variables and to ANY.
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.nf
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Example:
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.ft 5
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move REG1,REG2 { REG1[1] == REG2[1] + 1 }
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.ft R
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matches
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.ft 5
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move r1,r0
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move r2,r1
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move r3,r2
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.ft R
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.fi
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.PP
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The replacement part of a (pattern,replacement) table entry
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@ -311,10 +334,13 @@ Vax examples
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.PP
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Suppose the table contains the following declarations:
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.nf
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.ft 5
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X, LOG { TRUE };
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LAB { VAL[0] == 'L' }; /* e.g. L0017 */
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A { no_side_effects(VAL) };
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NUM { is_number(VAL) };
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.ft R
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.fi
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The procedure "no_side_effects" checks if its argument
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@ -324,23 +350,29 @@ These procedures must be supplied by the table-writer and must be
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included in the table.
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.PP
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.nf
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\fIentry:\fR addl3 X,A,A -> addl2 X,A;
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.ft 5
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\fIentry:\fP addl3 X,A,A -> addl2 X,A;
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.ft R
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.fi
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This entry changes a 3-operand instruction into a cheaper 2-operand
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instruction.
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An optimization like:
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.nf
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.ft 5
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addl3 r0,(r2)+,(r2)+ -> addl2 r0,(r2)+
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.ft R
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.fi
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is illegal, as r2 should be incremented twice.
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Hence the second argument is required to
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be side-effect free.
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.PP
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.nf
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\fIentry:\fR addw2 $-NUM,X -> subw2 $NUM,X;
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.ft 5
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\fIentry:\fP addw2 $-NUM,X -> subw2 $NUM,X;
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.ft R
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.fi
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An instruction like "subw2 $5,r0" is cheaper
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@ -349,18 +381,22 @@ because constants in the range 0 to 63 are represented
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very efficiently on the Vax.
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.PP
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.nf
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\fIentry:\fR bitw $NUM,A : jneq LAB
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.ft 5
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\fIentry:\fP bitw $NUM,A : jneq LAB
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{ is_poweroftwo(NUM,LOG) } -> jbs $LOG,A,LAB;
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.ft R
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.fi
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A "bitw x,y" sets the condition codes to the bitwise "and" of
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x and y.
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A "jbs n,x,l" branches to l if bit n of x is set.
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So, for example, the following transformation is possible:
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.nf
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.ft 5
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bitw $32,r0 : jneq L0017 -> jbs $5,r0,L0017
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.ft R
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.fi
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The user-defined procedure "is_poweroftwo" checks if its first argument is
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a power of 2 and, if so, sets its second argument to the logarithm
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@ -373,18 +409,23 @@ PDP-11 examples
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.PP
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Suppose we have the following declarations:
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.nf
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.ft 5
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X { TRUE };
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A { no_side_effects(VAL) };
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L1, L2 { VAL[0] == 'I' };
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REG { VAL[0] == 'r' && VAL[1] >= '0' && VAL[1] <= '5' &&
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VAL[2] == '\\0' };
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.ft P
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.fi
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The implementation of "no_side_effects" may of course
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differ for the PDP-11 and the Vax.
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.PP
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.nf
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\fIentry:\fR mov REG,A : ANY A,X -> mov REG,A : ANY REG,X ;
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.ft 5
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\fIentry:\fP mov REG,A : ANY A,X -> mov REG,A : ANY REG,X ;
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.ft R
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.fi
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This entry implements register subsumption.
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@ -392,7 +433,9 @@ If A and REG hold the same value (which is true after "mov REG,A")
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and A is used as source (first) operand, it is cheaper to use REG instead.
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.PP
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.nf
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\fIentry:\fR jeq L1 : jbr L2 : labdef L1 -> jne L2 : labdef L1;
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.ft 5
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\fIentry:\fP jeq L1 : jbr L2 : labdef L1 -> jne L2 : labdef L1;
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.ft R
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.fi
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The "jeq L1" is a "skip over an unconditional jump". "labdef L1"
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@ -401,7 +444,9 @@ As the target optimizer has to know how such a definition
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looks like, this must be expressed in the table (see Appendix A).
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.PP
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.nf
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\fIentry:\fR add $01,X { carry_dead(REST) } -> inc X;
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.ft 5
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\fIentry:\fP add $01,X { carry_dead(REST) } -> inc X;
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.ft R
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.fi
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On the PDP-11, an add-one is not equivalent to an increment.
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@ -440,24 +485,32 @@ backwards,
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as it is possible that instructions that were rejected earlier now do match.
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For example, consider the following patterns:
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.DS
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.ft 5
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cmp $0, X -> tst X ;
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mov REG,X : tst X -> move REG.X ; /* redundant test */
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.ft R
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.DE
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If the input is:
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.DS
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.ft 5
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mov r0,foo : cmp $0,foo
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.ft R
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.DE
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then the first instruction is initially rejected.
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However, after the transformation
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.DS
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.ft 5
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cmp $0,foo -> tst foo
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.ft R
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.DE
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the following optimization is possible:
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.DS
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.ft 5
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mov r0,foo : tst foo -> mov r0,foo
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.ft R
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.DE
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.PP
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The window is implemented a a \fIqueue\fR.
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The window is implemented as a \fIqueue\fR.
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Matching takes place at the head of the queue.
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New instructions are added at the tail.
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If the window is moved forwards, the instruction at the head
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@ -619,7 +672,10 @@ These two files are compiled together with some machine-independent
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files to produce a target optimizer.
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.PP
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Topgen is implemented using
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the LL(1) parser generator system LLgen,
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the LL(1) parser generator system LLgen ,
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.[
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jacobs topics parser generation
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.]
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a powerful tool of the Amsterdam Compiler Kit.
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This system provides a flexible way of describing the syntax of the tables.
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The syntactical description of the table format included
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@ -646,13 +702,14 @@ optimizer description table format.
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This appendix is intended for table-writers.
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We use syntax rules for the description of the table format.
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The following notation is used:
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.nf
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{ a } zero or more of a
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[ a ] zero or one of a
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a b a followed by b
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a | b a or b
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.fi
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.TS
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center;
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l l.
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{ a } zero or more of a
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[ a ] zero or one of a
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a b a followed by b
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a | b a or b
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.TE
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Terminals are given in quotes, as in ';'.
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.PP
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The table may contain white space and comment at all reasonable places.
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@ -661,35 +718,40 @@ Identifiers are sequences of letters, digits and the underscore ('_'),
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beginning with a letter.
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.PP
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.DS
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.ft 5
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table -> {parameter_line} '%%;' {variable_declaration} '%%;'
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{entry} '%%;' user_routines.
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.ft R
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.DE
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A table consists of four sections, containing machine-dependent
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constants, variable declarations, pattern rules and
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user-supplied subroutines.
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.PP
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.DS
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.ft 5
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parameter_line -> identifier value ';' .
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.ft R
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.DE
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A parameter line defines some attributes of the target machines
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assembly code.
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For unspecified parameters default values apply.
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The names of the parameters and the corresponding defaults
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are shown in table 1.
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.DS
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OPC_TERMINATOR ' '
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OP_SEPARATOR ','
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LABEL_STARTER 'I'
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LABEL_TERMINATOR ':'
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MAXOP 2
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MAXOPLEN 25
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MAX_OPC_LEN 10
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MAXVARLEN 25
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MAXLINELEN 100
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table 1: parameter names and defaults
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.TS
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center;
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l l.
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OPC_TERMINATOR ' '
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OP_SEPARATOR ','
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LABEL_STARTER 'I'
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LABEL_TERMINATOR ':'
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MAXOP 2
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MAXOPLEN 25
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MAX_OPC_LEN 10
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MAXVARLEN 25
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MAXLINELEN 100
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.TE
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.ce 1
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table 1: parameter names and defaults
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.DE
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The OPC_TERMINATOR is the character that separates the instruction
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mnemonic from the first operand (if any).
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@ -717,9 +779,11 @@ the line is not optimized.
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Optimization does, however, proceed with the rest of the input.
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.PP
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.DS
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.ft 5
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variable_declaration -> identifier {',' identifier} restriction ';' .
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restriction -> '{' anything '}' .
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.ft R
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.DE
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A variable declaration declares one or more string variables
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that may be used in the patterns and in the replacements.
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@ -739,6 +803,7 @@ Inside the expression, the name VAL stands for the part of the actual
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The expression may contain calls to procedures that are defined in the
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user-routines section.
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.DS
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.ft 5
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entry -> pattern '->' replacement ';' .
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pattern -> instruction_descr
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@ -760,6 +825,7 @@ operand_descr -> [ string_constant ]
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variable_name -> identifier .
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opcode -> anything .
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.ft R
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.DE
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The symbol 'white' stands for white space (space or tab).
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An opcode can be any string not containing the special
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@ -783,7 +849,9 @@ which contains the mnemonic of the first instruction of the
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rest of the input. (REST is a null-string if this mnemonic can
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not be determined).
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.DS
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.ft 5
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user_routines -> anything .
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.ft R
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.DE
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The remainder of the table consists of user-defined subroutines.
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.bp
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