From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Wed, 6 Jan 2016 08:59:32 +0000 (+0000)
Subject: [X86][SSE] An empty target shuffle mask is always a failure.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=fd8d45a8f8e830b8e8b81ad28a1a6d37568d719f;p=oota-llvm.git

[X86][SSE] An empty target shuffle mask is always a failure.

As discussed on D15378, move the mask.empty() tests to after the switch statement and consider any shuffle decode where the extracted target shuffle mask is empty as a failure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256921 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index b9863d1dea2..cedadff364d 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -4853,8 +4853,6 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
 
     if (auto *C = dyn_cast<Constant>(MaskCP->getConstVal())) {
       DecodePSHUFBMask(C, Mask);
-      if (Mask.empty())
-        return false;
       break;
     }
 
@@ -4872,7 +4870,6 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
   case X86ISD::VPERM2X128:
     ImmN = N->getOperand(N->getNumOperands()-1);
     DecodeVPERM2X128Mask(VT, cast<ConstantSDNode>(ImmN)->getZExtValue(), Mask);
-    if (Mask.empty()) return false;
     // Mask only contains negative index if an element is zero.
     if (std::any_of(Mask.begin(), Mask.end(),
                     [](int M){ return M == SM_SentinelZero; }))
@@ -4950,8 +4947,6 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
 
     if (auto *C = dyn_cast<Constant>(MaskCP->getConstVal())) {
       DecodeVPERMVMask(C, VT, Mask);
-      if (Mask.empty())
-        return false;
       break;
     }
     return false;
@@ -5002,8 +4997,6 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
 
     if (auto *C = dyn_cast<Constant>(MaskCP->getConstVal())) {
       DecodeVPERMV3Mask(C, VT, Mask);
-      if (Mask.empty())
-        return false;
       break;
     }
     return false;
@@ -5011,6 +5004,10 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
   default: llvm_unreachable("unknown target shuffle node");
   }
 
+  // Empty mask indicates the decode failed.
+  if (Mask.empty())
+    return false;
+
   // If we have a fake unary shuffle, the shuffle mask is spread across two
   // inputs that are actually the same node. Re-map the mask to always point
   // into the first input.