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Emit better x86_64 asm for constant loads

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Instead of always emitting movabs, emit a regular mov or a xor.
Slims down sequences like:

    movabs $0,%rax
    mov %rsi,%rax

To:

    xor %eax,%eax  // also zeroes upper word
    mov %rsi,%rax

Future work is to just emit:

    xor %esi,%esi
This commit is contained in:
Ben Noordhuis 2024-10-10 22:46:14 +02:00
parent b668b72b06
commit c21576f8a3
1 changed files with 9 additions and 2 deletions
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9
x86_64-gen.c
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@ -489,8 +489,15 @@ void load(int r, SValue *sv)
}
#endif
} else if (is64_type(ft)) {
orex(1,r,0, 0xb8 + REG_VALUE(r)); /* mov $xx, r */
if (sv->c.i > UINT32_MAX) {
orex(1,r,0, 0xb8 + REG_VALUE(r)); /* movabs $xx, r */
gen_le64(sv->c.i);
} else if (sv->c.i > 0) {
orex(0,r,0, 0xb8 + REG_VALUE(r)); /* mov $xx, r */
gen_le32(sv->c.i);
} else {
o(0xc031 + REG_VALUE(r) * 0x900); /* xor r, r */
}
} else {
orex(0,r,0, 0xb8 + REG_VALUE(r)); /* mov $xx, r */
gen_le32(fc);