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i386: We can change 'lea 0(%ebp),r' to 'mov %ebp,r'

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Because that mov is 1 byte shorter, look:

    int *func()
    {
        return __builtin_frame_address(0);
    }

before patch:

00000000 <func>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   81 ec 00 00 00 00       sub    $0x0,%esp
   9:   8d 45 00                lea    0x0(%ebp),%eax   // <- here
   c:   e9 00 00 00 00          jmp    11 <func+0x11>
  11:   c9                      leave
  12:   c3                      ret

after patch:

00000000 <func>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   81 ec 00 00 00 00       sub    $0x0,%esp
   9:   89 e8                   mov    %ebp,%eax        // <- here
   b:   e9 00 00 00 00          jmp    10 <func+0x10>
  10:   c9                      leave
  11:   c3                      ret
This commit is contained in:
Kirill Smelkov 2012-11-16 00:04:56 +04:00
parent b2a02961b4
commit ab24aaeca3
1 changed files with 7 additions and 2 deletions
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9
i386-gen.c
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@ -260,8 +260,13 @@ ST_FUNC void load(int r, SValue *sv)
o(0xb8 + r); /* mov $xx, r */
gen_addr32(fr, sv->sym, fc);
} else if (v == VT_LOCAL) {
o(0x8d); /* lea xxx(%ebp), r */
gen_modrm(r, VT_LOCAL, sv->sym, fc);
if (fc) {
o(0x8d); /* lea xxx(%ebp), r */
gen_modrm(r, VT_LOCAL, sv->sym, fc);
} else {
o(0x89);
o(0xe8 + r); /* mov %ebp, r */
}
} else if (v == VT_CMP) {
oad(0xb8 + r, 0); /* mov $0, r */
o(0x0f); /* setxx %br */