X86: use sub-register sequences for MOV*r0 operations
Instead of having a bunch of separate MOV8r0, MOV16r0, ... pseudo-instructions,
it's better to use a single MOV32r0 (which will expand to "xorl %reg, %reg")
and obtain other sizes with EXTRACT_SUBREG and SUBREG_TO_REG. The encoding is
smaller and partial register updates can sometimes be avoided.
Until recently, this sequence was a barrier to rematerialization though. That
should now be fixed so it's an appropriate time to make the change.
llvm-svn: 182928
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 4f0c2f2..5ed8604 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -1713,37 +1713,16 @@
unsigned DestReg, unsigned SubIdx,
const MachineInstr *Orig,
const TargetRegisterInfo &TRI) const {
- DebugLoc DL = Orig->getDebugLoc();
-
- // MOV32r0 etc. are implemented with xor which clobbers condition code.
- // Re-materialize them as movri instructions to avoid side effects.
- bool Clone = true;
+ // MOV32r0 is implemented with a xor which clobbers condition code.
+ // Re-materialize it as movri instructions to avoid side effects.
unsigned Opc = Orig->getOpcode();
- switch (Opc) {
- default: break;
- case X86::MOV8r0:
- case X86::MOV16r0:
- case X86::MOV32r0:
- case X86::MOV64r0: {
- if (!isSafeToClobberEFLAGS(MBB, I)) {
- switch (Opc) {
- default: llvm_unreachable("Unreachable!");
- case X86::MOV8r0: Opc = X86::MOV8ri; break;
- case X86::MOV16r0: Opc = X86::MOV16ri; break;
- case X86::MOV32r0: Opc = X86::MOV32ri; break;
- case X86::MOV64r0: Opc = X86::MOV64ri64i32; break;
- }
- Clone = false;
- }
- break;
- }
- }
-
- if (Clone) {
+ if (Opc == X86::MOV32r0 && !isSafeToClobberEFLAGS(MBB, I)) {
+ DebugLoc DL = Orig->getDebugLoc();
+ BuildMI(MBB, I, DL, get(X86::MOV32ri)).addOperand(Orig->getOperand(0))
+ .addImm(0);
+ } else {
MachineInstr *MI = MBB.getParent()->CloneMachineInstr(Orig);
MBB.insert(I, MI);
- } else {
- BuildMI(MBB, I, DL, get(Opc)).addOperand(Orig->getOperand(0)).addImm(0);
}
MachineInstr *NewMI = prior(I);
@@ -3364,10 +3343,7 @@
// MOV32r0 etc. are implemented with xor which clobbers condition code.
// They are safe to move up, if the definition to EFLAGS is dead and
// earlier instructions do not read or write EFLAGS.
- if (!Movr0Inst && (Instr->getOpcode() == X86::MOV8r0 ||
- Instr->getOpcode() == X86::MOV16r0 ||
- Instr->getOpcode() == X86::MOV32r0 ||
- Instr->getOpcode() == X86::MOV64r0) &&
+ if (!Movr0Inst && Instr->getOpcode() == X86::MOV32r0 &&
Instr->registerDefIsDead(X86::EFLAGS, TRI)) {
Movr0Inst = Instr;
continue;
@@ -3760,18 +3736,11 @@
OpcodeTablePtr = &RegOp2MemOpTable2Addr;
isTwoAddrFold = true;
} else if (i == 0) { // If operand 0
- unsigned Opc = 0;
- switch (MI->getOpcode()) {
- default: break;
- case X86::MOV64r0: Opc = X86::MOV64mi32; break;
- case X86::MOV32r0: Opc = X86::MOV32mi; break;
- case X86::MOV16r0: Opc = X86::MOV16mi; break;
- case X86::MOV8r0: Opc = X86::MOV8mi; break;
+ if (MI->getOpcode() == X86::MOV32r0) {
+ NewMI = MakeM0Inst(*this, X86::MOV32mi, MOs, MI);
+ if (NewMI)
+ return NewMI;
}
- if (Opc)
- NewMI = MakeM0Inst(*this, Opc, MOs, MI);
- if (NewMI)
- return NewMI;
OpcodeTablePtr = &RegOp2MemOpTable0;
} else if (i == 1) {
@@ -4157,13 +4126,9 @@
if (isTwoAddr && NumOps >= 2 && OpNum < 2) {
OpcodeTablePtr = &RegOp2MemOpTable2Addr;
} else if (OpNum == 0) { // If operand 0
- switch (Opc) {
- case X86::MOV8r0:
- case X86::MOV16r0:
- case X86::MOV32r0:
- case X86::MOV64r0: return true;
- default: break;
- }
+ if (Opc == X86::MOV32r0)
+ return true;
+
OpcodeTablePtr = &RegOp2MemOpTable0;
} else if (OpNum == 1) {
OpcodeTablePtr = &RegOp2MemOpTable1;