When determining the new index for an insertelement, we may not assume that an

index greater than the size of the vector is invalid. The shuffle may be
shrinking the size of the vector. Fixes a crash!

Also drop the maximum recursion depth of the safety check for this
optimization to five.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183080 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 53fcb7154efb6f07e64bbe3498696ee586fa7c72..c76aa4c2e6cff24e0ed417033fe83f6516ef71c1 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -497,7 +497,7 @@ Instruction *InstCombiner::visitInsertElementInst(InsertElementInst &IE) {
 /// Return true if we can evaluate the specified expression tree if the vector
 /// elements were shuffled in a different order.
 static bool CanEvaluateShuffled(Value *V, ArrayRef<int> Mask,
-                                unsigned Depth = 100) {
+                                unsigned Depth = 5) {
   // We can always reorder the elements of a constant.
   if (isa<Constant>(V))
     return true;
@@ -718,19 +718,21 @@ InstCombiner::EvaluateInDifferentElementOrder(Value *V, ArrayRef<int> Mask) {
     }
     case Instruction::InsertElement: {
       int Element = cast<ConstantInt>(I->getOperand(2))->getLimitedValue();
-      if (Element < 0 || Element >= (int)Mask.size()) {
-        // Such instructions are valid and exhibit undefined behaviour.
-        return UndefValue::get(I->getType());
-      }
 
       // The insertelement was inserting at Element. Figure out which element
       // that becomes after shuffling. The answer is guaranteed to be unique
       // by CanEvaluateShuffled.
+      bool Found = false;
       int Index = 0;
-      for (int e = Mask.size(); Index != e; ++Index)
-        if (Mask[Index] == Element)
+      for (int e = Mask.size(); Index != e; ++Index) {
+        if (Mask[Index] == Element) {
+          Found = true;
           break;
+        }
+      }
 
+      if (!Found)
+        return UndefValue::get(I->getType());
       Value *V = EvaluateInDifferentElementOrder(I->getOperand(0), Mask);
       return InsertElementInst::Create(V, I->getOperand(1),
                                        Builder->getInt32(Index), "", I);

diff --git a/test/Transforms/InstCombine/vec_shuffle.ll b/test/Transforms/InstCombine/vec_shuffle.ll
index 4b7a049baec82fbde8ba84d4a52ecd7f9287cbfc..5ffe6c04372fecc456001a972090f013e471ece1 100644 (file)
--- a/test/Transforms/InstCombine/vec_shuffle.ll
+++ b/test/Transforms/InstCombine/vec_shuffle.ll
@@ -174,3 +174,14 @@ define <2 x i8> @test13b(i8 %x) {
   %B = shufflevector <2 x i8> %A, <2 x i8> undef, <2 x i32> <i32 undef, i32 0>
   ret <2 x i8> %B
 }
+
+define <2 x i8> @test13c(i8 %x1, i8 %x2) {
+; CHECK: @test13c
+; CHECK-NEXT: insertelement <2 x i8> {{.*}}, i32 0
+; CHECK-NEXT: insertelement <2 x i8> {{.*}}, i32 1
+; CHECK-NEXT: ret
+  %A = insertelement <4 x i8> undef, i8 %x1, i32 0
+  %B = insertelement <4 x i8> %A, i8 %x2, i32 2
+  %C = shufflevector <4 x i8> %B, <4 x i8> undef, <2 x i32> <i32 0, i32 2>
+  ret <2 x i8> %C
+}