From 933cccf3fa81a928a026a88483d30d202c6b048e Mon Sep 17 00:00:00 2001
From: Filipe Cabecinhas <me@filcab.net>
Date: Thu, 24 Jul 2014 01:28:21 +0000
Subject: [PATCH] Fixed PR20411 - bug in getINSERTPS()

When we had a vector_shuffle where we had an input from each vector, we
could miscompile it because we were assuming the input from V2 wouldn't
be moved from where it was on the vector.

Added a test case.

llvm-svn: 213826
---
 llvm/lib/Target/X86/X86ISelLowering.cpp | 14 ++++++++++++++
 llvm/test/CodeGen/X86/sse41.ll          | 18 ++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 81889d0a7458..06a61cbba642 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -9063,6 +9063,18 @@ static SDValue getINSERTPS(ShuffleVectorSDNode *SVOp, SDLoc &dl,
     To = V2;
     DestIndex = std::find_if(Mask.begin(), Mask.end(), FromV1Predicate) -
                 Mask.begin();
+
+    // If we have 1 element from each vector, we have to check if we're
+    // changing V1's element's place. If so, we're done. Otherwise, we
+    // should assume we're changing V2's element's place and behave
+    // accordingly.
+    int FromV2 = std::count_if(Mask.begin(), Mask.end(), FromV2Predicate);
+    if (FromV1 == FromV2 && DestIndex == Mask[DestIndex] % 4) {
+      From = V2;
+      To = V1;
+      DestIndex =
+          std::find_if(Mask.begin(), Mask.end(), FromV2Predicate) - Mask.begin();
+    }
   } else {
     assert(std::count_if(Mask.begin(), Mask.end(), FromV2Predicate) == 1 &&
            "More than one element from V1 and from V2, or no elements from one "
@@ -9074,6 +9086,8 @@ static SDValue getINSERTPS(ShuffleVectorSDNode *SVOp, SDLoc &dl,
         std::find_if(Mask.begin(), Mask.end(), FromV2Predicate) - Mask.begin();
   }
 
+  // Get an index into the source vector in the range [0,4) (the mask is
+  // in the range [0,8) because it can address V1 and V2)
   unsigned SrcIndex = Mask[DestIndex] % 4;
   if (MayFoldLoad(From)) {
     // Trivial case, when From comes from a load and is only used by the
diff --git a/llvm/test/CodeGen/X86/sse41.ll b/llvm/test/CodeGen/X86/sse41.ll
index 6726a3ea9ff5..986488f531ec 100644
--- a/llvm/test/CodeGen/X86/sse41.ll
+++ b/llvm/test/CodeGen/X86/sse41.ll
@@ -714,3 +714,21 @@ define <4 x float> @pr20087(<4 x float> %a, <4 x float> *%ptr) {
   %ret = shufflevector <4 x float> %load, <4 x float> %a, <4 x i32> <i32 4, i32 undef, i32 6, i32 2>
   ret <4 x float> %ret
 }
+
+; Edge case for insertps where we end up with a shuffle with mask=<0, 7, -1, -1>
+define void @insertps_pr20411(i32* noalias nocapture %RET) #1 {
+; CHECK-LABEL: insertps_pr20411:
+; CHECK: movaps  {{[^,]*}}, %[[REG1:xmm.]]
+; CHECK: pshufd  {{.*}} ## [[REG2:xmm.]] = mem[3,0,0,0]
+; CHECK: insertps  {{.*}} ## xmm1 = [[REG2]][0],[[REG1]][3]{{.*}}
+
+  %gather_load = shufflevector <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>, <8 x i32> undef, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+  %shuffle109 = shufflevector <4 x i32> <i32 4, i32 5, i32 6, i32 7>, <4 x i32> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 3>  ; 4 5 6 7
+
+  %shuffle116 = shufflevector <8 x i32> %gather_load, <8 x i32> undef, <4 x i32> <i32 3, i32 undef, i32 undef, i32 undef> ; 3 x x x
+  %shuffle117 = shufflevector <4 x i32> %shuffle109, <4 x i32> %shuffle116, <4 x i32> <i32 4, i32 3, i32 undef, i32 undef> ; 3 7 x x
+
+  %ptrcast = bitcast i32* %RET to <4 x i32>*
+  store <4 x i32> %shuffle117, <4 x i32>* %ptrcast, align 4
+  ret void
+}