Properly handle PHIs with subregisters in UnreachableBlockElim
When a PHI operand has a subregister, create a COPY instead of simply
replacing the PHI output with the input it.
Differential Revision: https://reviews.llvm.org/D32650
llvm-svn: 301699
diff --git a/llvm/lib/CodeGen/UnreachableBlockElim.cpp b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
index c2db56a..f085132 100644
--- a/llvm/lib/CodeGen/UnreachableBlockElim.cpp
+++ b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
@@ -25,6 +25,7 @@
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -195,18 +196,30 @@
}
if (phi->getNumOperands() == 3) {
- unsigned Input = phi->getOperand(1).getReg();
- unsigned Output = phi->getOperand(0).getReg();
-
- phi++->eraseFromParent();
+ const MachineOperand &Input = phi->getOperand(1);
+ const MachineOperand &Output = phi->getOperand(0);
+ unsigned InputReg = Input.getReg();
+ unsigned OutputReg = Output.getReg();
+ assert(Output.getSubReg() == 0 && "Cannot have output subregister");
ModifiedPHI = true;
- if (Input != Output) {
+ if (InputReg != OutputReg) {
MachineRegisterInfo &MRI = F.getRegInfo();
- MRI.constrainRegClass(Input, MRI.getRegClass(Output));
- MRI.replaceRegWith(Output, Input);
+ unsigned InputSub = Input.getSubReg();
+ if (InputSub == 0) {
+ MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg));
+ MRI.replaceRegWith(OutputReg, InputReg);
+ } else {
+ // The input register to the PHI has a subregister:
+ // insert a COPY instead of simply replacing the output
+ // with the input.
+ const TargetInstrInfo *TII = F.getSubtarget().getInstrInfo();
+ BuildMI(*BB, BB->getFirstNonPHI(), phi->getDebugLoc(),
+ TII->get(TargetOpcode::COPY), OutputReg)
+ .addReg(InputReg, getRegState(Input), InputSub);
+ }
+ phi++->eraseFromParent();
}
-
continue;
}