[llvm] [HashRecognize] Fix LHS ConstantRange check for BE (PR #148620)

[Ramkumar Ramachandra via llvm-commits]

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@@ -198,35 +199,38 @@ KnownBits ValueEvolution::computeInstr(const Instruction *I) {
                         m_Instruction(FV)))) {
     Visited.insert(cast<Instruction>(I->getOperand(0)));
 
-    // We need to check LCR against [0, 2) in the little-endian case, because
-    // the RCR check is insufficient: it is simply [0, 1).
-    if (!ByteOrderSwapped) {
-      KnownBits KnownL = compute(L);
-      unsigned ICmpBW = KnownL.getBitWidth();
-      auto LCR = ConstantRange::fromKnownBits(KnownL, false);
-      auto CheckLCR = ConstantRange(APInt::getZero(ICmpBW), APInt(ICmpBW, 2));
-      if (LCR != CheckLCR) {
-        ErrStr = "Bad LHS of significant-bit-check";
-        return {BitWidth};
-      }
+    // Check that the predication is on (most|least) significant bit.
+    KnownBits KnownL = compute(L);
+    unsigned ICmpBW = KnownL.getBitWidth();
+    auto LCR = ConstantRange::fromKnownBits(KnownL, false);
+    // Check LCR against full-set, [0, -1), [0, -3), [0, -7), etc. depending on
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artagnon wrote:

Yes, that's exactly right. Will post an explanation shortly.

https://github.com/llvm/llvm-project/pull/148620