[llvm] [LV] Add vplan folds for urem(X, PowerOf2) -> and(X, PowerOf2 - 1) (PR #212198)

[David Sherwood via llvm-commits]

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@@ -1372,6 +1323,17 @@ static void simplifyRecipe(VPSingleDefRecipe *Def) {
   }
 
   const APInt *APC;
+  // TODO: Enable optimizations in the vector preheader in a follow-up PR.
+  // This check currently means we only simplify before region dissolution.
+  VPBasicBlock *Preheader = Plan->getVectorPreheader();
+  if (CanCreateNewRecipe && Preheader && Def->getParent() != Preheader &&
+      match(Def, m_URem(m_VPValue(X), m_APInt(APC))) && APC->isPowerOf2()) {
+    APInt APC2(*APC);
+    APC2 -= 1;
+    return Def->replaceAllUsesWith(
+        Builder.createAnd(X, Plan->getConstantInt(APC2)));
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david-arm wrote:

Unfortunately there is no easy way to get the name from a `VPSingleDefRecipe`, since it doesn't have one. Only certain recipes like VPInstruction seem to have a name.

https://github.com/llvm/llvm-project/pull/212198