[llvm] [VPlan] Reassociate (x & y) & z -> x & (y & z) (PR #155383)

[Luke Lau via llvm-commits]

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@@ -1119,6 +1119,15 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
     return;
   }
 
+  // Reassociate (x && y) && z -> x && (y && z) if x has multiple users. With
+  // tail folding it is likely that x is a header mask and can be simplified
+  // further.
+  if (match(Def, m_LogicalAnd(m_LogicalAnd(m_VPValue(X), m_VPValue(Y)),
+                              m_VPValue(Z))) &&
+      X->hasMoreThanOneUniqueUser())
+    return Def->replaceAllUsesWith(
+        Builder.createLogicalAnd(X, Builder.createLogicalAnd(X, Y)));
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lukel97 wrote:

Fixed in 7661966. I ran this again on SPEC CPU 2017 for RISC-V and there's still the original codegen improvements from the initial version of this PR where we remove the header mask in more places

https://github.com/llvm/llvm-project/pull/155383