[PATCH] D145129: [X86] Fix undefined access in `matchUnaryPermuteShuffle`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n created this revision.
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Move the opcode check on `Shuffle` to after we have already checked
that we found a valid shift instruction (`0 < ShiftAmt`).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145129

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp


Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -38829,12 +38829,13 @@
       int ShiftAmt =
           matchShuffleAsShift(ShuffleVT, Shuffle, MaskScalarSizeInBits, Mask, 0,
                               Zeroable, Subtarget);
-      // Byte shifts can be slower so only match them on second attempt.
-      if (Order == 0 &&
-          (Shuffle == X86ISD::VSHLDQ || Shuffle == X86ISD::VSRLDQ))
-        continue;
       if (0 < ShiftAmt && (!ShuffleVT.is512BitVector() || Subtarget.hasBWI() ||
                            32 <= ShuffleVT.getScalarSizeInBits())) {
+        // Byte shifts can be slower so only match them on second attempt.
+        if (Order == 0 &&
+            (Shuffle == X86ISD::VSHLDQ || Shuffle == X86ISD::VSRLDQ))
+          continue;
+
         PermuteImm = (unsigned)ShiftAmt;
         return true;
       }


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