From 5448a3c7717efab65f173070be6ce8270deb548e Mon Sep 17 00:00:00 2001
From: Andrea Di Biagio <Andrea_DiBiagio@sn.scee.net>
Date: Tue, 14 Jan 2014 13:17:12 +0000
Subject: [PATCH] [X86] Fix assertion failure caused by a wrong folding of
 vector shifts by immediate count.

This fixes a regression intruced by r198113.

Revision r198113 introduced an algorithm that tries to fold a vector shift
by immediate count into a build_vector if the input vector is a known vector
of constants.

However the algorithm only worked under the assumption that the input vector
type and the shift type are exactly the same.

This patch disables the folding of vector shift by immediate count if the
input vector type and the shift value type are not the same.

llvm-svn: 199213
---
 llvm/lib/Target/X86/X86ISelLowering.cpp |  5 ++--
 llvm/test/CodeGen/X86/vshift-6.ll       | 36 +++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/vshift-6.ll

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a41faab73b4b..ef1bd7fd3015 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -11118,8 +11118,9 @@ static SDValue getTargetVShiftByConstNode(unsigned Opc, SDLoc dl, MVT VT,
          && "Unknown target vector shift-by-constant node");
 
   // Fold this packed vector shift into a build vector if SrcOp is a
-  // vector of ConstantSDNodes or UNDEFs.
-  if (ISD::isBuildVectorOfConstantSDNodes(SrcOp.getNode())) {
+  // vector of Constants or UNDEFs, and SrcOp valuetype is the same as VT.
+  if (VT == SrcOp.getSimpleValueType() &&
+      ISD::isBuildVectorOfConstantSDNodes(SrcOp.getNode())) {
     SmallVector<SDValue, 8> Elts;
     unsigned NumElts = SrcOp->getNumOperands();
     ConstantSDNode *ND;
diff --git a/llvm/test/CodeGen/X86/vshift-6.ll b/llvm/test/CodeGen/X86/vshift-6.ll
new file mode 100644
index 000000000000..f50d9a6bb124
--- /dev/null
+++ b/llvm/test/CodeGen/X86/vshift-6.ll
@@ -0,0 +1,36 @@
+; RUN: llc < %s -mcpu=corei7 -march=x86-64 -mattr=+sse2  | FileCheck %s
+
+; This test makes sure that the compiler does not crash with an
+; assertion failure when trying to fold a vector shift left
+; by immediate count if the type of the input vector is different
+; to the result type.
+;
+; This happens for example when lowering a shift left of a MVT::v16i8 vector.
+; This is custom lowered into the following sequence:
+;     count << 5
+;     A =  VSHLI(MVT::v8i16, r & (char16)15, 4)
+;     B = BITCAST MVT::v16i8, A
+;     VSELECT(r, B, count);
+;     count += count
+;     C = VSHLI(MVT::v8i16, r & (char16)63, 2)
+;     D = BITCAST MVT::v16i8, C
+;     r = VSELECT(r, C, count);
+;     count += count
+;     VSELECT(r, r+r, count);
+;     count = count << 5;
+;
+; Where 'r' is a vector of type MVT::v16i8, and
+; 'count' is the vector shift count.
+
+define <16 x i8> @do_not_crash(i8*, i32*, i64*, i32, i64, i8) {
+entry:
+  store i8 %5, i8* %0
+  %L5 = load i8* %0
+  %I8 = insertelement <16 x i8> <i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>, i8 %L5, i32 7
+  %B51 = shl <16 x i8> <i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>, %I8
+  ret <16 x i8> %B51
+}
+
+; CHECK-LABEL: do_not_crash
+; CHECK: ret
+