[llvm] [VPlan] Add convertToUniformRecipe transform. (PR #139150)

[Luke Lau via llvm-commits]

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@@ -1084,6 +1084,40 @@ void VPlanTransforms::simplifyRecipes(VPlan &Plan, Type &CanonicalIVTy) {
   }
 }
 
+static void convertToUniformRecipes(VPlan &Plan) {
+  auto TryToNarrow = [](VPBasicBlock *VPBB) {
+    for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB))) {
+      // Try to narrow wide and replicating recipes to uniform recipes, based on
+      // VPlan analysis.
+      auto *Def = dyn_cast<VPSingleDefRecipe>(&R);
+      if (!Def || !isa<VPReplicateRecipe, VPWidenRecipe>(Def) ||
+          !Def->getUnderlyingValue())
+        continue;
+
+      auto *RepR = dyn_cast<VPReplicateRecipe>(&R);
+      if (RepR && RepR->isUniform())
+        continue;
+
+      // Skip recipes that aren't uniform and don't have only their scalar
+      // results used. In the later case, we would introduce extra broadcasts.
+      if (!vputils::isUniformAfterVectorization(Def) ||
+          any_of(Def->users(),
+                 [Def](VPUser *U) { return !U->usesScalars(Def); }))
+        continue;
+
+      auto *Clone = new VPReplicateRecipe(Def->getUnderlyingInstr(),
+                                          Def->operands(), /*IsUniform*/ true);
+      Clone->insertBefore(Def);
+      Def->replaceAllUsesWith(Clone);
+      Def->eraseFromParent();
+    }
+  };
+
+  for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
+           vp_depth_first_shallow(Plan.getVectorLoopRegion()->getEntry())))
+    TryToNarrow(VPBB);
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lukel97 wrote:

Is there a particular reason we're using a lambda here?

https://github.com/llvm/llvm-project/pull/139150