https://llvm.org/bugs/show_bug.cgi?id=28238
Bug ID: 28238
Summary: [InstCombine] icmp slt 0 optimization hinders more
optimization
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Spinning this off from bug 27869 (and may have a different solution than bug
28221):
int f(int i) {
return (i == 0) & (i >> 31);
}
'i' can't be 0 and have a bit set, so this should return 0.
$ ./clang -O1 sneaky_icmp.c -S -o - -emit-llvm
...
define i32 @f(i32 %i) {
%cmp = icmp eq i32 %i, 0
%conv = zext i1 %cmp to i32
%shr = ashr i32 %i, 31
%and = and i32 %conv, %shr
ret i32 %and
}
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