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Properly handle PHIs with subregisters in UnreachableBlockElim

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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
This commit is contained in:
Krzysztof Parzyszek 2017-04-28 21:56:33 +00:00
parent 68037e84f0
commit 819efa21ff
2 changed files with 46 additions and 8 deletions
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29
lib/CodeGen/UnreachableBlockElim.cpp
View File

@ -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 @@ bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
}
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;
}

25
test/CodeGen/Hexagon/unreachable-mbb-phi-subreg.mir Normal file
View File

@ -0,0 +1,25 @@
# RUN: llc -march=hexagon -run-pass unreachable-mbb-elimination %s -o - | FileCheck %s
---
name: fred
tracksRegLiveness: true
body: |
bb.0:
liveins: %d0
successors: %bb.2
%0 : doubleregs = COPY %d0
J2_jump %bb.2, implicit-def %pc
bb.1:
successors: %bb.2
A2_nop
bb.2:
; Make sure that the subregister from the PHI operand is preserved.
; CHECK: %[[REG:[0-9]+]] = COPY %0.isub_lo
; CHECK: %r0 = COPY %[[REG]]
%1 : intregs = PHI %0.isub_lo, %bb.0, %0.isub_hi, %bb.1
%r0 = COPY %1
...