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Handle a COPY with undef source operand in LowerCopy() 

Llvm-stress discovered that a COPY may end up in ExpandPostRA::LowerCopy()
with an undef source operand. It is not possible for the target to handle
this, as this flag is not passed to TII->copyPhysReg().

This patch solves this by treating such a COPY as an identity COPY.

Review: Matthias Braun
https://reviews.llvm.org/D32892

llvm-svn: 302877
This commit is contained in:
Jonas Paulsson 2017-05-12 06:32:03 +00:00
parent ce3ec4519b
commit d1ec738502
2 changed files with 17 additions and 2 deletions
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5
llvm/lib/CodeGen/ExpandPostRAPseudos.cpp
View File

@ -142,8 +142,9 @@ bool ExpandPostRA::LowerCopy(MachineInstr *MI) {
MachineOperand &DstMO = MI->getOperand(0);
MachineOperand &SrcMO = MI->getOperand(1);
if (SrcMO.getReg() == DstMO.getReg()) {
DEBUG(dbgs() << "identity copy: " << *MI);
bool IdentityCopy = (SrcMO.getReg() == DstMO.getReg());
if (IdentityCopy || SrcMO.isUndef()) {
DEBUG(dbgs() << (IdentityCopy ? "identity copy: " : "undef copy: ") << *MI);
// No need to insert an identity copy instruction, but replace with a KILL
// if liveness is changed.
if (SrcMO.isUndef() || MI->getNumOperands() > 2) {

14
llvm/test/CodeGen/SystemZ/lower-copy-undef-src.mir Normal file
View File

@ -0,0 +1,14 @@
# RUN: llc -mtriple=s390x-linux-gnu -mcpu=z13 -run-pass=postrapseudos -o - %s | FileCheck %s
#
# Test that a COPY with an undef source operand gets handled like an identity
# copy rather than lowered into a target instruction with the undef flag
# dropped.
---
# CHECK-LABEL: name: undef_copy
# CHECK: %r13d = KILL undef %r0d, implicit killed %r12q, implicit-def %r12q
name: undef_copy
tracksRegLiveness: true
body: |
bb.0:
liveins: %r12q
%r13d = COPY undef %r0d, implicit killed %r12q, implicit-def %r12q