[x86] fix remaining miscompile bug in horizontal binop matching (PR40243)

When we use the partial-matching function on a 128-bit chunk, we must
account for the possibility that we've matched undef halves of the
original source vectors, so the outputs may need to be reset.

This should allow closing PR40243:
https://bugs.llvm.org/show_bug.cgi?id=40243

llvm-svn: 350830

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 277fa2d..1695bc5 100644 (file)
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -8370,7 +8370,6 @@ static SDValue LowerToHorizontalOp(const BuildVectorSDNode *BV,
   SDLoc DL(BV);
   SDValue InVec0, InVec1;
   if (VT == MVT::v8i32 || VT == MVT::v16i16) {
-    // Try to match an AVX2 horizontal add/sub of signed integers.
     SDValue InVec2, InVec3;
     unsigned X86Opcode;
     bool CanFold = true;
@@ -8397,12 +8396,16 @@ static SDValue LowerToHorizontalOp(const BuildVectorSDNode *BV,
       if (NumUndefsLO + 1 == Half || NumUndefsHI + 1 == Half)
         return SDValue();
 
-      // Convert this build_vector into a pair of horizontal binop followed by
-      // a concat vector.
+      // Convert this build_vector into a pair of horizontal binops followed by
+      // a concat vector. We must adjust the outputs from the partial horizontal
+      // matching calls above to account for undefined vector halves.
+      SDValue V0 = InVec0.isUndef() ? InVec2 : InVec0;
+      SDValue V1 = InVec1.isUndef() ? InVec3 : InVec1;
+      assert((!V0.isUndef() || !V1.isUndef()) && "Horizontal-op of undefs?");
       bool isUndefLO = NumUndefsLO == Half;
       bool isUndefHI = NumUndefsHI == Half;
-      return ExpandHorizontalBinOp(InVec0, InVec1, DL, DAG, X86Opcode, false,
-                                   isUndefLO, isUndefHI);
+      return ExpandHorizontalBinOp(V0, V1, DL, DAG, X86Opcode, false, isUndefLO,
+                                   isUndefHI);
     }
   }
 

diff --git a/llvm/test/CodeGen/X86/phaddsub-undef.ll b/llvm/test/CodeGen/X86/phaddsub-undef.ll
index c827665..f763dbe 100644 (file)
--- a/llvm/test/CodeGen/X86/phaddsub-undef.ll
+++ b/llvm/test/CodeGen/X86/phaddsub-undef.ll
@@ -101,6 +101,10 @@ define <8 x i32> @PR40243_alt(<8 x i32> %a, <8 x i32> %b) {
 ;
 ; AVX1-LABEL: PR40243_alt:
 ; AVX1:       # %bb.0:
+; AVX1-NEXT:    vextractf128 $1, %ymm1, %xmm1
+; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm0
+; AVX1-NEXT:    vphaddd %xmm1, %xmm0, %xmm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: PR40243_alt: