[GlobalISel][AArch64] Select store of zero to WZR/XZR.
These occur very frequently, and are quite trivial to catch.
llvm-svn: 298862
diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
index 2e199d9..146eea0 100644
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -775,6 +775,17 @@
I.setDesc(TII.get(NewOpc));
I.addOperand(MachineOperand::CreateImm(0));
+
+ // If we're storing a 0, use WZR/XZR.
+ if (auto CVal = getConstantVRegVal(ValReg, MRI)) {
+ if (*CVal == 0 && Opcode == TargetOpcode::G_STORE) {
+ if (I.getOpcode() == AArch64::STRWui)
+ I.getOperand(0).setReg(AArch64::WZR);
+ else if (I.getOpcode() == AArch64::STRXui)
+ I.getOperand(0).setReg(AArch64::XZR);
+ }
+ }
+
return constrainSelectedInstRegOperands(I, TII, TRI, RBI);
}