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add note about va_arg code on x86 and x86-64

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llvm-svn: 58103
This commit is contained in:
Torok Edwin 2008-10-24 19:20:05 +00:00
parent cfd2ecd29f
commit 5560590122
1 changed files with 94 additions and 0 deletions
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94
lib/Target/README.txt
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@ -985,3 +985,97 @@ define i1 @test(i8 %x) {
//===---------------------------------------------------------------------===//
This code:
int foo(const char *str,...)
{
__builtin_va_list a; int x;
__builtin_va_start(a,str); x = __builtin_va_arg(a,int); __builtin_va_end(a);
return x;
}
gets compiled into this on x86-64:
subq $200, %rsp
movaps %xmm7, 160(%rsp)
movaps %xmm6, 144(%rsp)
movaps %xmm5, 128(%rsp)
movaps %xmm4, 112(%rsp)
movaps %xmm3, 96(%rsp)
movaps %xmm2, 80(%rsp)
movaps %xmm1, 64(%rsp)
movaps %xmm0, 48(%rsp)
movq %r9, 40(%rsp)
movq %r8, 32(%rsp)
movq %rcx, 24(%rsp)
movq %rdx, 16(%rsp)
movq %rsi, 8(%rsp)
leaq (%rsp), %rax
movq %rax, 192(%rsp)
leaq 208(%rsp), %rax
movq %rax, 184(%rsp)
movl $48, 180(%rsp)
movl $8, 176(%rsp)
movl 176(%rsp), %eax
cmpl $47, %eax
jbe .LBB1_3 # bb
.LBB1_1: # bb3
movq 184(%rsp), %rcx
leaq 8(%rcx), %rax
movq %rax, 184(%rsp)
.LBB1_2: # bb4
movl (%rcx), %eax
addq $200, %rsp
ret
.LBB1_3: # bb
movl %eax, %ecx
addl $8, %eax
addq 192(%rsp), %rcx
movl %eax, 176(%rsp)
jmp .LBB1_2 # bb4
gcc 4.3 generates:
subq $96, %rsp
.LCFI0:
leaq 104(%rsp), %rax
movq %rsi, -80(%rsp)
movl $8, -120(%rsp)
movq %rax, -112(%rsp)
leaq -88(%rsp), %rax
movq %rax, -104(%rsp)
movl $8, %eax
cmpl $48, %eax
jb .L6
movq -112(%rsp), %rdx
movl (%rdx), %eax
addq $96, %rsp
ret
.p2align 4,,10
.p2align 3
.L6:
mov %eax, %edx
addq -104(%rsp), %rdx
addl $8, %eax
movl %eax, -120(%rsp)
movl (%rdx), %eax
addq $96, %rsp
ret
and it gets compiled into this on x86:
pushl %ebp
movl %esp, %ebp
subl $4, %esp
leal 12(%ebp), %eax
movl %eax, -4(%ebp)
leal 16(%ebp), %eax
movl %eax, -4(%ebp)
movl 12(%ebp), %eax
addl $4, %esp
popl %ebp
ret
gcc 4.3 generates:
pushl %ebp
movl %esp, %ebp
movl 12(%ebp), %eax
popl %ebp
ret