http://llvm.org/bugs/show_bug.cgi?id=16486
Bug ID: 16486
Summary: Regression: Emits worse sequence for conditional move
operation
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
consider the following:
define i32 @_Z4blahiiii(i32 %a, i32 %b, i32 %c, i32 %d) #0 {
entry:
%cmp = icmp sgt i32 %a, %b
%add = add nsw i32 %a, %c
%add1 = add nsw i32 %b, %d
%x.0 = select i1 %cmp, i32 %add, i32 %add1
ret i32 %x.0
}
this leaves us with:
addl %edi, %edx
addl %esi, %ecx
cmpl %esi, %edi
cmovgl %edx, %ecx
movl %ecx, %eax
ret
however, if we swap around operands a bit:
define i32 @_Z4blahiiii(i32 %a, i32 %b, i32 %c, i32 %d) #0 {
entry:
%cmp = icmp sgt i32 %a, %b
%add = add nsw i32 %c, %a
%add1 = add nsw i32 %d, %b
%x.0 = select i1 %cmp, i32 %add, i32 %add1
ret i32 %x.0
}
we instead get:
addl %edi, %edx
leal (%rcx,%rsi), %eax
cmpl %esi, %edi
cmovgl %edx, %eax
ret
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