[llvm] [SVE][InstCombine] Delete redundante sel instructions with ptrue (PR #68463)

[via llvm-commits]

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@@ -798,8 +798,30 @@ instCombineConvertFromSVBool(InstCombiner &IC, IntrinsicInst &II) {
   return IC.replaceInstUsesWith(II, EarliestReplacement);
 }
 
+static bool isAllActivePredicate(Value *Pred) {
+  // Look through convert.from.svbool(convert.to.svbool(...) chain.
+  Value *UncastedPred;
+  if (match(Pred, m_Intrinsic<Intrinsic::aarch64_sve_convert_from_svbool>(
+                      m_Intrinsic<Intrinsic::aarch64_sve_convert_to_svbool>(
+                          m_Value(UncastedPred)))))
+    // If the predicate has the same or less lanes than the uncasted
+    // predicate then we know the casting has no effect.
+    if (cast<ScalableVectorType>(Pred->getType())->getMinNumElements() <=
+        cast<ScalableVectorType>(UncastedPred->getType())->getMinNumElements())
+      Pred = UncastedPred;
+
+  return match(Pred, m_Intrinsic<Intrinsic::aarch64_sve_ptrue>(
+                         m_ConstantInt<AArch64SVEPredPattern::all>()));
+}
+
 static std::optional<Instruction *> instCombineSVESel(InstCombiner &IC,
                                                       IntrinsicInst &II) {
+  // svsel(ptrue, x, y) => x
+  auto *OpPredicate = II.getOperand(0);
+  if (isAllActivePredicate(OpPredicate)) {
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vfdff wrote:

Updated the stylistic according comment, thanks

https://github.com/llvm/llvm-project/pull/68463