[llvm] [VPlan] Don't emit VPBlendRecipes with only one incoming value. NFC (PR #171804)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Luke Lau (lukel97)

<details>
<summary>Changes</summary>

We can just directly use the incoming value. These single value blends would get optimized later on in simplifyBlends, but by doing it early it removes the notion of an "immediately normalized" blend, and simplifies an upcoming patch.


---
Full diff: https://github.com/llvm/llvm-project/pull/171804.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/VPlan.h (+1-1) 
- (modified) llvm/lib/Transforms/Vectorize/VPlanPredicator.cpp (+7-8) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index 2ef7b5405668d..0f8f6abab7b0a 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -2517,7 +2517,7 @@ class LLVM_ABI_FOR_TEST VPBlendRecipe : public VPSingleDefRecipe {
   /// all other incoming values are merged into it.
   VPBlendRecipe(PHINode *Phi, ArrayRef<VPValue *> Operands, DebugLoc DL)
       : VPSingleDefRecipe(VPDef::VPBlendSC, Operands, Phi, DL) {
-    assert(Operands.size() > 0 && "Expected at least one operand!");
+    assert(Operands.size() >= 2 && "Expected at least two operands!");
   }
 
   VPBlendRecipe *clone() override {
diff --git a/llvm/lib/Transforms/Vectorize/VPlanPredicator.cpp b/llvm/lib/Transforms/Vectorize/VPlanPredicator.cpp
index 6517862e2d0f8..f7e7fc29bc203 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanPredicator.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanPredicator.cpp
@@ -240,17 +240,16 @@ void VPPredicator::convertPhisToBlends(VPBasicBlock *VPBB) {
     // be duplications since this is a simple recursive scan, but future
     // optimizations will clean it up.
 
+    if (all_equal(PhiR->incoming_values())) {
+      PhiR->replaceAllUsesWith(PhiR->getIncomingValue(0));
+      PhiR->eraseFromParent();
+      continue;
+    }
+
     SmallVector<VPValue *, 2> OperandsWithMask;
     for (const auto &[InVPV, InVPBB] : PhiR->incoming_values_and_blocks()) {
       OperandsWithMask.push_back(InVPV);
-      VPValue *EdgeMask = getEdgeMask(InVPBB, VPBB);
-      if (!EdgeMask) {
-        assert(all_equal(PhiR->incoming_values()) &&
-               "Distinct incoming values with one having a full mask");
-        break;
-      }
-
-      OperandsWithMask.push_back(EdgeMask);
+      OperandsWithMask.push_back(getEdgeMask(InVPBB, VPBB));
     }
     PHINode *IRPhi = cast_or_null<PHINode>(PhiR->getUnderlyingValue());
     auto *Blend =

``````````

</details>


https://github.com/llvm/llvm-project/pull/171804