Merging r197228:

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r197228 | d0k | 2013-12-13 05:40:24 -0800 (Fri, 13 Dec 2013) | 8 lines

X86: When lowering shl_parts, don't emit shift amounts larger than the bit width.

While it's safe for the X86-specific shift nodes, dag combining will
kill generic nodes. Insert an AND to make it safe, isel will nuke it
as x86's shift instructions have an implicit AND.

Fixes PR16108, which contains a contraption to hit this case in between
constant folders.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@197321 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 2 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 12d40c488a..d0667ff54a 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -8424,6 +8424,11 @@ SDValue X86TargetLowering::LowerShiftParts(SDValue Op, SelectionDAG &DAG) const{
   SDValue ShOpLo = Op.getOperand(0);
   SDValue ShOpHi = Op.getOperand(1);
   SDValue ShAmt  = Op.getOperand(2);
+  // X86ISD::SHLD and X86ISD::SHRD have defined overflow behavior but the
+  // generic ISD nodes haven't. Insert an AND to be safe, it's optimized away
+  // during isel.
+  SDValue SafeShAmt = DAG.getNode(ISD::AND, dl, MVT::i8, ShAmt,
+                                  DAG.getConstant(VTBits - 1, MVT::i8));
   SDValue Tmp1 = isSRA ? DAG.getNode(ISD::SRA, dl, VT, ShOpHi,
                                      DAG.getConstant(VTBits - 1, MVT::i8))
                        : DAG.getConstant(0, VT);
@@ -8431,12 +8436,15 @@ SDValue X86TargetLowering::LowerShiftParts(SDValue Op, SelectionDAG &DAG) const{
   SDValue Tmp2, Tmp3;
   if (Op.getOpcode() == ISD::SHL_PARTS) {
     Tmp2 = DAG.getNode(X86ISD::SHLD, dl, VT, ShOpHi, ShOpLo, ShAmt);
-    Tmp3 = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, ShAmt);
+    Tmp3 = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, SafeShAmt);
   } else {
     Tmp2 = DAG.getNode(X86ISD::SHRD, dl, VT, ShOpLo, ShOpHi, ShAmt);
-    Tmp3 = DAG.getNode(isSRA ? ISD::SRA : ISD::SRL, dl, VT, ShOpHi, ShAmt);
+    Tmp3 = DAG.getNode(isSRA ? ISD::SRA : ISD::SRL, dl, VT, ShOpHi, SafeShAmt);
   }
 
+  // If the shift amount is larger or equal than the width of a part we can't
+  // rely on the results of shld/shrd. Insert a test and select the appropriate
+  // values for large shift amounts.
   SDValue AndNode = DAG.getNode(ISD::AND, dl, MVT::i8, ShAmt,
                                 DAG.getConstant(VTBits, MVT::i8));
   SDValue Cond = DAG.getNode(X86ISD::CMP, dl, MVT::i32,