[llvm] [VPlan] Avoid sinking allocas in sinkScalarOperands (PR #166135)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-vectorizers

Author: Ramkumar Ramachandra (artagnon)

<details>
<summary>Changes</summary>

Use cannotHoistOrSinkRecipe to forbid sinking allocas.

---
Full diff: https://github.com/llvm/llvm-project/pull/166135.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp (+1-2) 
- (modified) llvm/test/Transforms/LoopVectorize/tail-folding-alloca-in-loop.ll (+7-4) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index b45536869c5af..b646fec53993f 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -161,8 +161,7 @@ static bool sinkScalarOperands(VPlan &Plan) {
     if (!isa<VPReplicateRecipe, VPScalarIVStepsRecipe>(Candidate))
       return false;
 
-    if (Candidate->getParent() == SinkTo || Candidate->mayHaveSideEffects() ||
-        Candidate->mayReadOrWriteMemory())
+    if (Candidate->getParent() == SinkTo || cannotHoistOrSinkRecipe(*Candidate))
       return false;
 
     if (auto *RepR = dyn_cast<VPReplicateRecipe>(Candidate))
diff --git a/llvm/test/Transforms/LoopVectorize/tail-folding-alloca-in-loop.ll b/llvm/test/Transforms/LoopVectorize/tail-folding-alloca-in-loop.ll
index a852b731ea13b..9e523be618b44 100644
--- a/llvm/test/Transforms/LoopVectorize/tail-folding-alloca-in-loop.ll
+++ b/llvm/test/Transforms/LoopVectorize/tail-folding-alloca-in-loop.ll
@@ -12,12 +12,15 @@ define i32 @test(ptr %vf1, i64 %n) {
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[PRED_STORE_CONTINUE6:.*]] ]
 ; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i8> [ <i8 0, i8 1, i8 2, i8 3>, %[[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], %[[PRED_STORE_CONTINUE6]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = icmp ule <4 x i8> [[VEC_IND]], splat (i8 -56)
+; CHECK-NEXT:    [[TMP18:%.*]] = alloca i8, i64 [[N]], align 16
+; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x ptr> poison, ptr [[TMP18]], i64 0
+; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x ptr> [[BROADCAST_SPLATINSERT]], <4 x ptr> poison, <4 x i32> zeroinitializer
 ; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <4 x i1> [[TMP0]], i32 0
 ; CHECK-NEXT:    br i1 [[TMP1]], label %[[PRED_STORE_IF:.*]], label %[[PRED_STORE_CONTINUE:.*]]
 ; CHECK:       [[PRED_STORE_IF]]:
 ; CHECK-NEXT:    [[TMP2:%.*]] = add i64 [[INDEX]], 0
 ; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds ptr, ptr [[VF1]], i64 [[TMP2]]
-; CHECK-NEXT:    [[TMP4:%.*]] = alloca i8, i64 [[N]], align 16
+; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <4 x ptr> [[BROADCAST_SPLAT]], i32 0
 ; CHECK-NEXT:    store ptr [[TMP4]], ptr [[TMP3]], align 8
 ; CHECK-NEXT:    br label %[[PRED_STORE_CONTINUE]]
 ; CHECK:       [[PRED_STORE_CONTINUE]]:
@@ -26,7 +29,7 @@ define i32 @test(ptr %vf1, i64 %n) {
 ; CHECK:       [[PRED_STORE_IF1]]:
 ; CHECK-NEXT:    [[TMP6:%.*]] = add i64 [[INDEX]], 1
 ; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr inbounds ptr, ptr [[VF1]], i64 [[TMP6]]
-; CHECK-NEXT:    [[TMP8:%.*]] = alloca i8, i64 [[N]], align 16
+; CHECK-NEXT:    [[TMP8:%.*]] = extractelement <4 x ptr> [[BROADCAST_SPLAT]], i32 0
 ; CHECK-NEXT:    store ptr [[TMP8]], ptr [[TMP7]], align 8
 ; CHECK-NEXT:    br label %[[PRED_STORE_CONTINUE2]]
 ; CHECK:       [[PRED_STORE_CONTINUE2]]:
@@ -35,7 +38,7 @@ define i32 @test(ptr %vf1, i64 %n) {
 ; CHECK:       [[PRED_STORE_IF3]]:
 ; CHECK-NEXT:    [[TMP10:%.*]] = add i64 [[INDEX]], 2
 ; CHECK-NEXT:    [[TMP11:%.*]] = getelementptr inbounds ptr, ptr [[VF1]], i64 [[TMP10]]
-; CHECK-NEXT:    [[TMP12:%.*]] = alloca i8, i64 [[N]], align 16
+; CHECK-NEXT:    [[TMP12:%.*]] = extractelement <4 x ptr> [[BROADCAST_SPLAT]], i32 0
 ; CHECK-NEXT:    store ptr [[TMP12]], ptr [[TMP11]], align 8
 ; CHECK-NEXT:    br label %[[PRED_STORE_CONTINUE4]]
 ; CHECK:       [[PRED_STORE_CONTINUE4]]:
@@ -44,7 +47,7 @@ define i32 @test(ptr %vf1, i64 %n) {
 ; CHECK:       [[PRED_STORE_IF5]]:
 ; CHECK-NEXT:    [[TMP14:%.*]] = add i64 [[INDEX]], 3
 ; CHECK-NEXT:    [[TMP15:%.*]] = getelementptr inbounds ptr, ptr [[VF1]], i64 [[TMP14]]
-; CHECK-NEXT:    [[TMP16:%.*]] = alloca i8, i64 [[N]], align 16
+; CHECK-NEXT:    [[TMP16:%.*]] = extractelement <4 x ptr> [[BROADCAST_SPLAT]], i32 0
 ; CHECK-NEXT:    store ptr [[TMP16]], ptr [[TMP15]], align 8
 ; CHECK-NEXT:    br label %[[PRED_STORE_CONTINUE6]]
 ; CHECK:       [[PRED_STORE_CONTINUE6]]:

``````````

</details>


https://github.com/llvm/llvm-project/pull/166135