[llvm] r215095 - [x86] Fix another miscompile found through fuzz testing the new vector

[Chandler Carruth]

Author: chandlerc
Date: Thu Aug  7 05:37:35 2014
New Revision: 215095

URL: http://llvm.org/viewvc/llvm-project?rev=215095&view=rev
Log:
[x86] Fix another miscompile found through fuzz testing the new vector
shuffle lowering.

This is closely related to the previous one. Here we failed to use the
source offset when swapping in the other case -- where we end up
swapping the *final* shuffle. The cause of this bug is a bit different:
I simply wasn't thinking about the fact that this mask is actually
a slice of a wide mask and thus has numbers that need SourceOffset
applied. Simple fix. Would be even more simple with an algorithm-y thing
to use here, but correctness first. =]

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
    llvm/trunk/test/CodeGen/X86/vector-shuffle-128-v8.ll

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=215095&r1=215094&r2=215095&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Thu Aug  7 05:37:35 2014
@@ -7546,10 +7546,10 @@ static SDValue lowerV8I16SingleInputVect
           // We also have to update the final source mask in this case because
           // it may need to undo the above swap.
           for (int &M : FinalSourceHalfMask)
-            if (M == (InputsFixed[0] ^ 1))
-              M = InputsFixed[1];
-            else if (M == InputsFixed[1])
-              M = InputsFixed[0] ^ 1;
+            if (M == (InputsFixed[0] ^ 1) + SourceOffset)
+              M = InputsFixed[1] + SourceOffset;
+            else if (M == InputsFixed[1] + SourceOffset)
+              M = InputsFixed[0] ^ 1 + SourceOffset;
 
           InputsFixed[1] = InputsFixed[0] ^ 1;
         }

Modified: llvm/trunk/test/CodeGen/X86/vector-shuffle-128-v8.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vector-shuffle-128-v8.ll?rev=215095&r1=215094&r2=215095&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/vector-shuffle-128-v8.ll (original)
+++ llvm/trunk/test/CodeGen/X86/vector-shuffle-128-v8.ll Thu Aug  7 05:37:35 2014
@@ -238,6 +238,23 @@ define <8 x i16> @shuffle_v8i16_66751643
   ret <8 x i16> %shuffle
 }
 
+define <8 x i16> @shuffle_v8i16_60514754(<8 x i16> %a, <8 x i16> %b) {
+; SSE2-LABEL: @shuffle_v8i16_60514754
+; SSE2:       # BB#0:
+; SSE2-NEXT:    pshufhw {{.*}} # xmm0 = xmm0[0,1,2,3,6,5,4,7]
+; SSE2-NEXT:    pshufd {{.*}} # xmm0 = xmm0[0,2,2,3]
+; SSE2-NEXT:    pshuflw {{.*}} # xmm0 = xmm0[2,0,3,1,4,5,6,7]
+; SSE2-NEXT:    pshufhw {{.*}} # xmm0 = xmm0[0,1,2,3,6,7,5,6]
+; SSE2-NEXT:    retq
+;
+; SSSE3-LABEL: @shuffle_v8i16_60514754
+; SSSE3:       # BB#0:
+; SSSE3-NEXT:    pshufb {{.*}} # xmm0 = xmm0[12,13,0,1,10,11,2,3,8,9,14,15,10,11,8,9]
+; SSSE3-NEXT:    retq
+  %shuffle = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 6, i32 0, i32 5, i32 1, i32 4, i32 7, i32 5, i32 4>
+  ret <8 x i16> %shuffle
+}
+
 define <8 x i16> @shuffle_v8i16_00444444(<8 x i16> %a, <8 x i16> %b) {
 ; SSE2-LABEL: @shuffle_v8i16_00444444
 ; SSE2:       # BB#0: