https://bugs.llvm.org/show_bug.cgi?id=44529
Bug ID: 44529
Summary: [InstCombine] Negation not sunk through shift
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
define i64 @test(i64 %a, i64 %b) {
%sub = sub i64 %a, %b
%mul = shl i64 %sub, 2
%neg = sub i64 0, %mul
ret i64 %neg
}
is not instcombined to
define i64 @test(i64 %a, i64 %b) {
%sub2 = sub i64 %b, %a
%neg = shl i64 %sub2, 2
ret i64 %neg
}
This pattern showed up as a regression when testing some instcombine worklist
order changes.
I guess the most general case of this would be handled by the negator in
https://reviews.llvm.org/D68408, though a much smaller gun would do in this
case as well.
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