From e4546cb71e14baa0cde8f85a12cfa8b2d44fe708 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 1 Jun 2013 20:51:31 +0000
Subject: [PATCH] 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
---
 .../InstCombine/InstCombineVectorOps.cpp         | 16 +++++++++-------
 test/Transforms/InstCombine/vec_shuffle.ll       | 11 +++++++++++
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 53fcb7154ef..c76aa4c2e6c 100644
--- 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 4b7a049baec..5ffe6c04372 100644
--- 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
+}