[llvm] [LLVM][InstCombine] Add simplification of SVE compare intrinsics. (PR #211249)

[Paul Walker via llvm-commits]

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@@ -1964,6 +2018,79 @@ simplifySVEIntrinsicBinOp(InstCombiner &IC, IntrinsicInst &II,
   return IC.replaceInstUsesWith(II, SimpleII);
 }
 
+static std::optional<Instruction *>
+simplifySVEIntrinsicCompare(InstCombiner &IC, IntrinsicInst &II,
+                            const SVEIntrinsicInfo &IInfo) {
+  const unsigned Opc = IInfo.getMatchingIROpode();
+  assert((Opc == Instruction::ICmp || Opc == Instruction::FCmp) &&
+         "Expected a compare operation!");
+
+  Value *Pg = II.getOperand(0);
+  Value *LHS = II.getOperand(1);
+  Value *RHS = II.getOperand(2);
+  CmpInst::Predicate CmpPred = IInfo.getCmpPredicate();
+  const DataLayout &DL = II.getDataLayout();
+
+  // Canonicalise integer constants to the RHS.
+  if (Opc == Instruction::ICmp && ICmpInst::isCommutative(CmpPred) &&
+      isa<Constant>(LHS) && !isa<Constant>(RHS) &&
+      LHS->getType() == RHS->getType()) {
+    IC.replaceOperand(II, 1, RHS);
+    IC.replaceOperand(II, 2, LHS);
+    return &II;
+  }
+
+  // Canonicalise floating-point constants to the RHS.
+  if (Opc == Instruction::FCmp && FCmpInst::isCommutative(CmpPred) &&
+      isa<Constant>(LHS) && !isa<Constant>(RHS)) {
+    assert(LHS->getType() == RHS->getType() && "Unexpected wide compare!");
+    IC.replaceOperand(II, 1, RHS);
+    IC.replaceOperand(II, 2, LHS);
+    return &II;
+  }
+
+  // Only active lanes matter when simplifying the operation.
+  LHS = stripInactiveLanes(LHS, Pg);
+  RHS = stripInactiveLanes(RHS, Pg);
+
+  if (LHS->getType() != RHS->getType()) {
+    // We can do more for wide compares, but not using simplifyCmpInst.
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paulwalker-arm wrote:

The assert exists to verify the expected inputs.  However, I've implemented your suggestion and so the assert is no longer necessary.

https://github.com/llvm/llvm-project/pull/211249