[PATCH] D103378: [VectorCombine] Freeze index unless it is known to be non-poison.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: spatel, nlopes.
Herald added subscribers: arphaman, hiraditya.
fhahn requested review of this revision.
Herald added a project: LLVM.

If the index itself is already poison, the poison propagates through
instructions clamping the index to a valid range. This still causes
introducing a load of poison, as flagged by Alive2 and pointed out
at 575e2aff5574 <https://reviews.llvm.org/rG575e2aff5574550d10278d9a41fca2926a5b8409>.

This patch updates the code to freeze the index, unless it is proven to
not be poison.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D103378

Files:
  llvm/lib/Transforms/Vectorize/VectorCombine.cpp
  llvm/test/Transforms/VectorCombine/AArch64/load-extractelement-scalarization.ll


Index: llvm/test/Transforms/VectorCombine/AArch64/load-extractelement-scalarization.ll
===================================================================
--- llvm/test/Transforms/VectorCombine/AArch64/load-extractelement-scalarization.ll
+++ llvm/test/Transforms/VectorCombine/AArch64/load-extractelement-scalarization.ll
@@ -147,8 +147,9 @@
 ; CHECK-LABEL: @load_extract_idx_var_i64_known_valid_by_and(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[IDX_CLAMPED:%.*]] = and i64 [[IDX:%.*]], 3
-; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds <4 x i32>, <4 x i32>* [[X:%.*]], i32 0, i64 [[IDX_CLAMPED]]
-; CHECK-NEXT:    [[R:%.*]] = load i32, i32* [[TMP0]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = freeze i64 [[IDX_CLAMPED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds <4 x i32>, <4 x i32>* [[X:%.*]], i32 0, i64 [[TMP0]]
+; CHECK-NEXT:    [[R:%.*]] = load i32, i32* [[TMP1]], align 4
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
 entry:
@@ -192,8 +193,9 @@
 ; CHECK-LABEL: @load_extract_idx_var_i64_known_valid_by_urem(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[IDX_CLAMPED:%.*]] = urem i64 [[IDX:%.*]], 4
-; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds <4 x i32>, <4 x i32>* [[X:%.*]], i32 0, i64 [[IDX_CLAMPED]]
-; CHECK-NEXT:    [[R:%.*]] = load i32, i32* [[TMP0]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = freeze i64 [[IDX_CLAMPED]]
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds <4 x i32>, <4 x i32>* [[X:%.*]], i32 0, i64 [[TMP0]]
+; CHECK-NEXT:    [[R:%.*]] = load i32, i32* [[TMP1]], align 4
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
 entry:
@@ -569,10 +571,12 @@
 ; CHECK-LABEL: @load_multiple_extracts_with_variable_indices_large_vector_all_valid_by_and(
 ; CHECK-NEXT:    [[IDX_0_CLAMPED:%.*]] = and i64 [[IDX_0:%.*]], 15
 ; CHECK-NEXT:    [[IDX_1_CLAMPED:%.*]] = and i64 [[IDX_1:%.*]], 15
-; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X:%.*]], i32 0, i64 [[IDX_0_CLAMPED]]
-; CHECK-NEXT:    [[E_0:%.*]] = load i32, i32* [[TMP1]], align 4
-; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X]], i32 0, i64 [[IDX_1_CLAMPED]]
-; CHECK-NEXT:    [[E_1:%.*]] = load i32, i32* [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = freeze i64 [[IDX_0_CLAMPED]]
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X:%.*]], i32 0, i64 [[TMP1]]
+; CHECK-NEXT:    [[E_0:%.*]] = load i32, i32* [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = freeze i64 [[IDX_1_CLAMPED]]
+; CHECK-NEXT:    [[TMP4:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X]], i32 0, i64 [[TMP3]]
+; CHECK-NEXT:    [[E_1:%.*]] = load i32, i32* [[TMP4]], align 4
 ; CHECK-NEXT:    [[RES:%.*]] = add i32 [[E_0]], [[E_1]]
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
@@ -590,10 +594,11 @@
 ; CHECK-LABEL: @load_multiple_extracts_with_variable_indices_large_vector_all_valid_by_and_some_noundef(
 ; CHECK-NEXT:    [[IDX_0_CLAMPED:%.*]] = and i64 [[IDX_0:%.*]], 15
 ; CHECK-NEXT:    [[IDX_1_CLAMPED:%.*]] = and i64 [[IDX_1:%.*]], 15
-; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X:%.*]], i32 0, i64 [[IDX_0_CLAMPED]]
-; CHECK-NEXT:    [[E_0:%.*]] = load i32, i32* [[TMP1]], align 4
-; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X]], i32 0, i64 [[IDX_1_CLAMPED]]
-; CHECK-NEXT:    [[E_1:%.*]] = load i32, i32* [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP1:%.*]] = freeze i64 [[IDX_0_CLAMPED]]
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X:%.*]], i32 0, i64 [[TMP1]]
+; CHECK-NEXT:    [[E_0:%.*]] = load i32, i32* [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds <16 x i32>, <16 x i32>* [[X]], i32 0, i64 [[IDX_1_CLAMPED]]
+; CHECK-NEXT:    [[E_1:%.*]] = load i32, i32* [[TMP3]], align 4
 ; CHECK-NEXT:    [[RES:%.*]] = add i32 [[E_0]], [[E_1]]
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
Index: llvm/lib/Transforms/Vectorize/VectorCombine.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -911,8 +911,13 @@
   for (User *U : LI->users()) {
     auto *EI = cast<ExtractElementInst>(U);
     Builder.SetInsertPoint(EI);
-    Value *GEP = Builder.CreateInBoundsGEP(
-        FixedVT, Ptr, {Builder.getInt32(0), EI->getOperand(1)});
+
+    Value *Idx = EI->getOperand(1);
+    if (!isGuaranteedNotToBePoison(Idx, &AC, LI, &DT))
+      Idx = Builder.CreateFreeze(Idx);
+
+    Value *GEP =
+        Builder.CreateInBoundsGEP(FixedVT, Ptr, {Builder.getInt32(0), Idx});
     auto *NewLoad = cast<LoadInst>(Builder.CreateLoad(
         FixedVT->getElementType(), GEP, EI->getName() + ".scalar"));
 


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