Add "mayHaveSideEffects" and "neverHasSideEffects" flags to some instructions. I

based what flag to set on whether it was already marked as
"isRematerializable". If there was a further check to determine if it's "really"
rematerializable, then I marked it as "mayHaveSideEffects" and created a check
in the X86 back-end similar to the remat one.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45132 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 34 insertions, 0 deletions

diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index 9d5e637119..d6d146f2a5 100644
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -144,6 +144,40 @@ bool X86InstrInfo::isReallyTriviallyReMaterializable(MachineInstr *MI) const {
   return true;
 }
 
+/// isReallySideEffectFree - If the M_MAY_HAVE_SIDE_EFFECTS flag is set, this
+/// method is called to determine if the specific instance of this instruction
+/// has side effects. This is useful in cases of instructions, like loads, which
+/// generally always have side effects. A load from a constant pool doesn't have
+/// side effects, though. So we need to differentiate it from the general case.
+bool X86InstrInfo::isReallySideEffectFree(MachineInstr *MI) const {
+  switch (MI->getOpcode()) {
+  default: break;
+  case X86::MOV8rm:
+  case X86::MOV16rm:
+  case X86::MOV16_rm:
+  case X86::MOV32rm:
+  case X86::MOV32_rm:
+  case X86::MOV64rm:
+  case X86::LD_Fp64m:
+  case X86::MOVSSrm:
+  case X86::MOVSDrm:
+  case X86::MOVAPSrm:
+  case X86::MOVAPDrm:
+  case X86::MMX_MOVD64rm:
+  case X86::MMX_MOVQ64rm:
+    // Loads from constant pools have no side effects
+    return MI->getOperand(1).isRegister() && MI->getOperand(2).isImmediate() &&
+           MI->getOperand(3).isRegister() && MI->getOperand(4).isConstantPoolIndex() &&
+           MI->getOperand(1).getReg() == 0 &&
+           MI->getOperand(2).getImmedValue() == 1 &&
+           MI->getOperand(3).getReg() == 0;
+  }
+
+  // All other instances of these instructions are presumed to have side
+  // effects.
+  return false;
+}
+
 /// hasLiveCondCodeDef - True if MI has a condition code def, e.g. EFLAGS, that
 /// is not marked dead.
 static bool hasLiveCondCodeDef(MachineInstr *MI) {