Use the new syntax in the mips, pdp, powerpc tables to declare
functions before calling them. These declarations prevent compiler
warnings about implicitly declaring functions. They also provide
prototypes of the function parameters.
Also fix a warning in the powerpc table: use `bsearch(...) != NULL` to
avoid converting the pointer from bsearch() to an int.
The syntax for topgen is a block `{...}` among the parameters in the
top table. It looks like the syntax of LLgen, but topgen doesn't
allow nested blocks, so declarations like `struct whatever {...};`
don't work. The token OPEN_BRACKET that begins a declaration_block
doesn't conflict with the LETTER that begins a parameter_line or the
'%' that begins a separator.
Because a block writes a #line command to gen.h, a parameter line now
also writes a #line command to gen.h, so it doesn't get a wrong line
number from a previous block.
If X < 0, then lowering the addi might cause the code to use the stack
space before allocating it. This is a bug because an asynchronous
signal handler can overwrite the unallocated stack space.
This reduces code size, because ncg emits too many "addi sp, sp, X"
instructions when unstacking things. Now top lowers "addi sp, sp, X"
by lifting other instructions. This sometimes creates chances to
merge or delete _addi_ instructions. If no such chance is found, the
_addi_ remains uselessly lowered.
Edit ncg/table to remove something that top now does.
Edit ncg/mach.c to remove some spaces after commas. This removes a
whitespace difference between *.s and *.so files, because top removes
the space.
Also don't delete addis r0, r0, 0. These instructions are special
cases that set r0 to zero. If we delete them, then r0 keeps its old
value.
I caught this bug because osxppc protects the .text segment against
writing. (linuxppc doesn't protect it.) A program tried to set r0 to
the NULL pointer, but top deleted the instruction, so r0 kept an old
return address pointing into .text. Later the program checked that r0
wasn't NULL, tried to write to address r0, and crashed.
