[llvm] [VPlan] Introduce CSE pass (PR #151872)

[Luke Lau via llvm-commits]

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@@ -1752,6 +1752,76 @@ void VPlanTransforms::clearReductionWrapFlags(VPlan &Plan) {
   }
 }
 
+/// Hash the underlying data of a VPSingleDefRecipe pointer, instead of hashing
+/// the pointer itself.
+namespace {
+struct VPCSEDenseMapInfo : public DenseMapInfo<VPSingleDefRecipe *> {
+  static bool isSentinel(const VPSingleDefRecipe *Def) {
+    return Def == getEmptyKey() || Def == getTombstoneKey();
+  }
+
+  static bool canHandle(const VPSingleDefRecipe *Def) {
+    return isa<VPInstruction, VPWidenRecipe, VPWidenCastRecipe,
+               VPWidenSelectRecipe, VPHistogramRecipe, VPPartialReductionRecipe,
+               VPReplicateRecipe, VPWidenIntrinsicRecipe>(Def);
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lukel97 wrote:

Which results was it regressing? I definitely don't think it's correct to CSE anything that has side effects. If something changed then it probably just needs added handled in `VPRecipeBase::mayHaveSideEffects`

https://github.com/llvm/llvm-project/pull/151872