https://bugs.llvm.org/show_bug.cgi?id=43595
Bug ID: 43595
Summary: [InstCombine] Failure to recognize sign bit test -
shift amount reassociation
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: lebedev...@gmail.com
CC: llvm-bugs@lists.llvm.org
This is motivated by https://bugs.llvm.org/show_bug.cgi?id=42389
While we succeed to produce sign bit test if we use unsigned:
https://godbolt.org/z/iSlCpW
We get stuck if we use signed:
https://godbolt.org/z/VO1-0F
Boo. https://rise4fun.com/Alive/PRU
I'm not sure how to approach this yet.
We can't treat this just as shift amount reassociation,
maybe icmp can be treated as `trunc to i1`.
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