[llvm-bugs] [Bug 46807] New: Merge 5b5dc2442ac7 into 11.0 release branch

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46807

            Bug ID: 46807
           Summary: Merge 5b5dc2442ac7 into 11.0 release branch
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: llvm-dev at redking.me.uk
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com
            Blocks: 46725

Based off an investigation into a test case provided by Craig, we need to avoid
traversing the DAG inside getTargetShuffleMask - I investigated hasOneUse()
wrappers but this approach is safer and we have other shuffle decode/combines
that can handle more complex broadcast shuffle folds.

Craig - are you OK with this getting merged?


https://reviews.llvm.org/rG5b5dc2442ac7

[X86][AVX] getTargetShuffleMask - don't decode
VBROADCAST(EXTRACT_SUBVECTOR(X,0)) patterns.

getTargetShuffleMask is used by the various "SimplifyDemanded" folds so we
can't assume that the bypassed extract_subvector can be safely simplified -
getFauxShuffleMask performs a more general decode that allows us to more safely
catch many of these cases so the impact is minimal.


Referenced Bugs:

https://bugs.llvm.org/show_bug.cgi?id=46725
[Bug 46725] [meta] 11.0.0 Release Blockers
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