https://bugs.llvm.org/show_bug.cgi?id=50008
Bug ID: 50008
Summary: Missing comparison folding optimization
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: juneyoung....@sf.snu.ac.kr
CC: llvm-bugs@lists.llvm.org
Optimization
(cond ? ptr + 1 : ptr == ptr) --> !cond
is missing in clang.
https://godbolt.org/z/e7W5WrK5M
bool not_cond(char *x, bool cond) {
char *y = x;
if (cond)
y = x + 1;
return x == y;
}
g++ -O3 (x86-64):
mov eax, esi
xor eax, 1
ret
clang -O3 (x86-64):
lea rax, [rdi + 1]
test esi, esi
cmove rax, rdi
cmp rax, rdi
sete al
ret
Similarly for AArch64.
It seems the middle-end optimization cannot fold this:
```
%add.ptr = getelementptr inbounds i8, i8* %x, i64 1
%spec.select = select i1 %cond, i8* %add.ptr, i8* %x
%cmp = icmp eq i8* %spec.select, %x
```
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