[llvm] [LLVM][InstCombine][SVE] Refactor sve.mul/fmul combines. (PR #134116)

[Sander de Smalen via llvm-commits]

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@@ -2206,45 +2229,63 @@ static std::optional<Instruction *> instCombineSVEVectorSub(InstCombiner &IC,
   return std::nullopt;
 }
 
-static std::optional<Instruction *> instCombineSVEVectorMul(InstCombiner &IC,
-                                                            IntrinsicInst &II) {
-  auto *OpPredicate = II.getOperand(0);
-  auto *OpMultiplicand = II.getOperand(1);
-  auto *OpMultiplier = II.getOperand(2);
+// Simplify `V` by only considering the operations that affect active lanes.
+// This function should only return existing Values or newly created Constants.
+static Value *stripInactiveLanes(Value *V, const Value *Pg) {
+  auto *Dup = dyn_cast<IntrinsicInst>(V);
+  if (Dup && Dup->getIntrinsicID() == Intrinsic::aarch64_sve_dup &&
+      Dup->getOperand(1) == Pg && isa<Constant>(Dup->getOperand(2)))
+    return ConstantVector::getSplat(
+        cast<VectorType>(V->getType())->getElementCount(),
+        cast<Constant>(Dup->getOperand(2)));
+
+  return V;
+}
 
-  // Return true if a given instruction is a unit splat value, false otherwise.
-  auto IsUnitSplat = [](auto *I) {
-    auto *SplatValue = getSplatValue(I);
-    if (!SplatValue)
-      return false;
-    return match(SplatValue, m_FPOne()) || match(SplatValue, m_One());
-  };
+static std::optional<Instruction *>
+instCombineSVEVectorMul(InstCombiner &IC, IntrinsicInst &II,
+                        const SVEIntrinsicInfo &IInfo) {
+  const unsigned Opc = IInfo.getMatchingIROpode();
+  if (!Instruction::isBinaryOp(Opc))
+    return std::nullopt;
 
-  // Return true if a given instruction is an aarch64_sve_dup intrinsic call
-  // with a unit splat value, false otherwise.
-  auto IsUnitDup = [](auto *I) {
-    auto *IntrI = dyn_cast<IntrinsicInst>(I);
-    if (!IntrI || IntrI->getIntrinsicID() != Intrinsic::aarch64_sve_dup)
-      return false;
+  Value *Pg = II.getOperand(0);
+  Value *Op1 = II.getOperand(1);
+  Value *Op2 = II.getOperand(2);
+  const DataLayout &DL = II.getDataLayout();
 
-    auto *SplatValue = IntrI->getOperand(2);
-    return match(SplatValue, m_FPOne()) || match(SplatValue, m_One());
-  };
+  // Canonicalise constants to the RHS.
+  if (Instruction::isCommutative(Opc) && IInfo.inactiveLanesAreNotDefined() &&
+      isa<Constant>(Op1) && !isa<Constant>(Op2)) {
+    IC.replaceOperand(II, 1, Op2);
+    IC.replaceOperand(II, 2, Op1);
+    return &II;
+  }
 
-  if (IsUnitSplat(OpMultiplier)) {
-    // [f]mul pg %n, (dupx 1) => %n
-    OpMultiplicand->takeName(&II);
-    return IC.replaceInstUsesWith(II, OpMultiplicand);
-  } else if (IsUnitDup(OpMultiplier)) {
-    // [f]mul pg %n, (dup pg 1) => %n
-    auto *DupInst = cast<IntrinsicInst>(OpMultiplier);
-    auto *DupPg = DupInst->getOperand(1);
-    // TODO: this is naive. The optimization is still valid if DupPg
-    // 'encompasses' OpPredicate, not only if they're the same predicate.
-    if (OpPredicate == DupPg) {
-      OpMultiplicand->takeName(&II);
-      return IC.replaceInstUsesWith(II, OpMultiplicand);
-    }
+  // Only active lanes matter when simplifying the operation.
+  Op1 = stripInactiveLanes(Op1, Pg);
+  Op2 = stripInactiveLanes(Op2, Pg);
----------------
sdesmalen-arm wrote:

Is there value in stripping the inactive lanes before the "Canonicalise constants to the RHS" above, so that the case above may hit more often? (e.g. a case of `svmul_x(svdup(..), svdup())`)

https://github.com/llvm/llvm-project/pull/134116