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[RegisterCoalescer] Don't set read-undef in pruneValues, only clear 

Summary:
The comments in the code said

 // Remove <def,read-undef> flags. This def is now a partial redef.

but the code didn't just remove read-undef, it could introduce new ones which
could cause errors.

E.g. if we have something like

%vreg1<def> = IMPLICIT_DEF
%vreg2:subreg1<def, read-undef> = op %vreg3, %vreg4
%vreg2:subreg2<def> = op %vreg6, %vreg7

and we merge %vreg1 and %vreg2 then we should not set undef on the second subreg
def, which the old code did.

Now we solve this by actually do what the code comment says. We remove
read-undef flags rather than remove or introduce them.

Reviewers: qcolombet, MatzeB

Reviewed By: MatzeB

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38616

llvm-svn: 315564
This commit is contained in:
Mikael Holmen 2017-10-12 06:21:28 +00:00
parent a84a47741a
commit a079ef68e3
2 changed files with 32 additions and 2 deletions
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4
llvm/lib/CodeGen/RegisterCoalescer.cpp
View File

@ -2685,8 +2685,8 @@ void JoinVals::pruneValues(JoinVals &Other,
for (MachineOperand &MO :
Indexes->getInstructionFromIndex(Def)->operands()) {
if (MO.isReg() && MO.isDef() && MO.getReg() == Reg) {
if (MO.getSubReg() != 0)
MO.setIsUndef(EraseImpDef);
if (MO.getSubReg() != 0 && MO.isUndef() && !EraseImpDef)
MO.setIsUndef(false);
MO.setIsDead(false);
}
}

30
llvm/test/CodeGen/MIR/X86/simple-register-allocation-read-undef.mir Normal file
View File

@ -0,0 +1,30 @@
# RUN: llc -mtriple=x86_64-- %s -o - -run-pass=simple-register-coalescing | FileCheck %s
---
name: f
body: |
bb.0:
JB_1 %bb.2, undef implicit killed %eflags
JMP_1 %bb.1
bb.1:
%0 : gr64 = IMPLICIT_DEF
NOOP implicit-def undef %1.sub_32bit : gr64
NOOP implicit-def %1.sub_16bit : gr64
JMP_1 %bb.3
bb.2:
NOOP implicit-def %0
%1 = COPY %0
bb.3:
NOOP implicit killed %0
NOOP implicit killed %1
...
# We should have a setting of both sub_32bit and sub_16bit. The first one
# should be undef and not dead, and the second should not be undef.
# CHECK-NOT: dead
# CHECK: NOOP implicit-def undef %1.sub_32bit
# CHECK-NOT: undef
# CHECK-NEXT: NOOP implicit-def %1.sub_16bit