[llvm] [LV][EVL] Simplify EVL recipe transformation by using a single EVL mask. nfc (PR #152479)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Mel Chen (Mel-Chen)

<details>
<summary>Changes</summary>

The EVL mask is always defined as `icmp ult (step-vector, EVL)`, so we only need to generate it once per plan in the header. Then, we replace all uses of the header mask with the EVL mask, and recursively optimize the users of EVL mask into EVL recipes. This way, the transformation to EVL recipes can be done with just a single loop.

---
Full diff: https://github.com/llvm/llvm-project/pull/152479.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp (+36-37) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 0cb704c85ba40..4afaa9c1ece53 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -2227,48 +2227,47 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
     }
   }
 
-  // Try to optimize header mask recipes away to their EVL variants.
+  // Replace header masks with a mask equivalent to predicating by EVL:
+  //
+  // icmp ule widen-canonical-iv backedge-taken-count
+  // ->
+  // icmp ult step-vector, EVL
+  VPRecipeBase *EVLR = EVL.getDefiningRecipe();
+  VPBuilder Builder(EVLR->getParent(), std::next(EVLR->getIterator()));
+  Type *EVLType = TypeInfo.inferScalarType(&EVL);
+  VPValue *EVLMask = Builder.createICmp(
+      CmpInst::ICMP_ULT,
+      Builder.createNaryOp(VPInstruction::StepVector, {}, EVLType), &EVL);
   for (VPValue *HeaderMask : collectAllHeaderMasks(Plan)) {
-    // TODO: Split optimizeMaskToEVL out and move into
-    // VPlanTransforms::optimize. transformRecipestoEVLRecipes should be run in
-    // tryToBuildVPlanWithVPRecipes beforehand.
-    for (VPUser *U : collectUsersRecursively(HeaderMask)) {
-      auto *CurRecipe = cast<VPRecipeBase>(U);
-      VPRecipeBase *EVLRecipe =
-          optimizeMaskToEVL(HeaderMask, *CurRecipe, TypeInfo, *AllOneMask, EVL);
-      if (!EVLRecipe)
-        continue;
-
-      [[maybe_unused]] unsigned NumDefVal = EVLRecipe->getNumDefinedValues();
-      assert(NumDefVal == CurRecipe->getNumDefinedValues() &&
-             "New recipe must define the same number of values as the "
-             "original.");
-      assert(
-          NumDefVal <= 1 &&
-          "Only supports recipes with a single definition or without users.");
-      EVLRecipe->insertBefore(CurRecipe);
-      if (isa<VPSingleDefRecipe, VPWidenLoadEVLRecipe>(EVLRecipe)) {
-        VPValue *CurVPV = CurRecipe->getVPSingleValue();
-        CurVPV->replaceAllUsesWith(EVLRecipe->getVPSingleValue());
-      }
-      ToErase.push_back(CurRecipe);
-    }
-
-    // Replace header masks with a mask equivalent to predicating by EVL:
-    //
-    // icmp ule widen-canonical-iv backedge-taken-count
-    // ->
-    // icmp ult step-vector, EVL
-    VPRecipeBase *EVLR = EVL.getDefiningRecipe();
-    VPBuilder Builder(EVLR->getParent(), std::next(EVLR->getIterator()));
-    Type *EVLType = TypeInfo.inferScalarType(&EVL);
-    VPValue *EVLMask = Builder.createICmp(
-        CmpInst::ICMP_ULT,
-        Builder.createNaryOp(VPInstruction::StepVector, {}, EVLType), &EVL);
     HeaderMask->replaceAllUsesWith(EVLMask);
     ToErase.push_back(HeaderMask->getDefiningRecipe());
   }
 
+  // Try to optimize header mask recipes away to their EVL variants.
+  // TODO: Split optimizeMaskToEVL out and move into
+  // VPlanTransforms::optimize. transformRecipestoEVLRecipes should be run in
+  // tryToBuildVPlanWithVPRecipes beforehand.
+  for (VPUser *U : collectUsersRecursively(EVLMask)) {
+    auto *CurRecipe = cast<VPRecipeBase>(U);
+    VPRecipeBase *EVLRecipe =
+        optimizeMaskToEVL(EVLMask, *CurRecipe, TypeInfo, *AllOneMask, EVL);
+    if (!EVLRecipe)
+      continue;
+
+    [[maybe_unused]] unsigned NumDefVal = EVLRecipe->getNumDefinedValues();
+    assert(NumDefVal == CurRecipe->getNumDefinedValues() &&
+           "New recipe must define the same number of values as the "
+           "original.");
+    assert(NumDefVal <= 1 &&
+           "Only supports recipes with a single definition or without users.");
+    EVLRecipe->insertBefore(CurRecipe);
+    if (isa<VPSingleDefRecipe, VPWidenLoadEVLRecipe>(EVLRecipe)) {
+      VPValue *CurVPV = CurRecipe->getVPSingleValue();
+      CurVPV->replaceAllUsesWith(EVLRecipe->getVPSingleValue());
+    }
+    ToErase.push_back(CurRecipe);
+  }
+
   for (VPRecipeBase *R : reverse(ToErase)) {
     SmallVector<VPValue *> PossiblyDead(R->operands());
     R->eraseFromParent();

``````````

</details>


https://github.com/llvm/llvm-project/pull/152479