[llvm] r344867 - [X86] Only extract constant pool shuffle mask data with zero offsets

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Sun Oct 21 04:55:56 2018
New Revision: 344867

URL: http://llvm.org/viewvc/llvm-project?rev=344867&view=rev
Log:
[X86] Only extract constant pool shuffle mask data with zero offsets

D53306 exposes an issue where we sometimes use constant pool data from bigger vectors than the target shuffle mask. This should be safe to do, but we have to be certain that we're using the bottom most part of the vector as the shuffle mask decoders have no way to peek into subvectors with non-zero offsets.

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
    llvm/trunk/lib/Target/X86/X86MCInstLower.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=344867&r1=344866&r2=344867&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sun Oct 21 04:55:56 2018
@@ -5536,7 +5536,7 @@ static const Constant *getTargetConstant
     Ptr = Ptr->getOperand(0);
 
   auto *CNode = dyn_cast<ConstantPoolSDNode>(Ptr);
-  if (!CNode || CNode->isMachineConstantPoolEntry())
+  if (!CNode || CNode->isMachineConstantPoolEntry() || CNode->getOffset() != 0)
     return nullptr;
 
   return dyn_cast<Constant>(CNode->getConstVal());

Modified: llvm/trunk/lib/Target/X86/X86MCInstLower.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86MCInstLower.cpp?rev=344867&r1=344866&r2=344867&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86MCInstLower.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86MCInstLower.cpp Sun Oct 21 04:55:56 2018
@@ -1379,7 +1379,7 @@ PrevCrossBBInst(MachineBasicBlock::const
 
 static const Constant *getConstantFromPool(const MachineInstr &MI,
                                            const MachineOperand &Op) {
-  if (!Op.isCPI())
+  if (!Op.isCPI() || Op.getOffset() != 0)
     return nullptr;
 
   ArrayRef<MachineConstantPoolEntry> Constants =