X86: do not fold load instructions such as [V]MOVS[S|D] to other instructions

when the destination register is wider than the memory load.

These load instructions load from m32 or m64 and set the upper bits to zero,
while the folded instructions may accept m128.

rdar://12721174

llvm-svn: 168710

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 5a99ff004d4..4e31af14eb6 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -3982,6 +3982,21 @@ MachineInstr* X86InstrInfo::foldMemoryOperandImpl(MachineFunction &MF,
     break;
   }
   default: {
+    if ((LoadMI->getOpcode() == X86::MOVSSrm ||
+         LoadMI->getOpcode() == X86::VMOVSSrm) &&
+        MF.getRegInfo().getRegClass(LoadMI->getOperand(0).getReg())->getSize()
+          > 4)
+      // These instructions only load 32 bits, we can't fold them if the
+      // destination register is wider than 32 bits (4 bytes).
+      return NULL;
+    if ((LoadMI->getOpcode() == X86::MOVSDrm ||
+         LoadMI->getOpcode() == X86::VMOVSDrm) &&
+        MF.getRegInfo().getRegClass(LoadMI->getOperand(0).getReg())->getSize()
+          > 8)
+      // These instructions only load 64 bits, we can't fold them if the
+      // destination register is wider than 64 bits (8 bytes).
+      return NULL;
+
     // Folding a normal load. Just copy the load's address operands.
     unsigned NumOps = LoadMI->getDesc().getNumOperands();
     for (unsigned i = NumOps - X86::AddrNumOperands; i != NumOps; ++i)