http://llvm.org/bugs/show_bug.cgi?id=8569
Summary: Missing assertion propagation
Product: new-bugs
Version: unspecified
Platform: PC
OS/Version: Linux
Status: NEW
Keywords: quality-of-implementation
Severity: normal
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected], [email protected]
Trivial Test:
int g;
int foo (int i)
{
if (i == 1)
{
g = i + 1;
}
else if (i == 10)
g = 2*i;
return g;
}
Clang -O2 -fomit-frame-pointer generates:
foo:
.Leh_func_begin0:
cmpl $1, %edi
je .LBB0_3
cmpl $10, %edi
je .LBB0_4
movl g(%rip), %eax
ret
.LBB0_3:
incl %edi <---
movl %edi, g(%rip) <---
movl $2, %eax
ret
.LBB0_4:
addl %edi, %edi <---
movl %edi, g(%rip) <---
movl $20, %eax
ret
Compared with gcc -O2 result:
.LFB0:
.cfi_startproc
cmpl $1, %edi
je .L6
cmpl $10, %edi
je .L4
movl g(%rip), %eax
ret
.p2align 4,,10
.p2align 3
.L4:
movl $20, g(%rip)
movl $20, %eax
ret
.p2align 4,,10
.p2align 3
.L6:
movl $2, g(%rip)
movl $2, %eax
ret
--
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