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Consider subregs when calling MI::registerDefIsDead for phys deps

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The scheduling dependency graph is built bottom-up within each scheduling
region, and ScheduleDAGInstrs::addPhysRegDeps is called to add output/anti
dependencies, based on physical registers, to the SUs for instructions
based on those that come before them.

In the test case, we start before post-RA scheduling with a block that looks
like this:

...
	INLINEASM <...
andc $0,$0,$2
stdcx. $0,0,$3
bne- 1b
> [sideeffect] [mayload] [maystore] [attdialect], $0:[regdef-ec:G8RC], %X6<earlyclobber,def,dead>, $1:[mem], %X3<kill>, $2:[reguse:G8RC], %X5<kill>, $3:[reguse:G8RC], %X3, $4:[mem], %X3, $5:[clobber], %CC<earlyclobber,imp-def,dead>, <<badref>>
	...
	%X4<def,dead> = ANDIo8 %X4<kill>, 1, %CR0<imp-def,dead>, %CR0GT<imp-def>
	...
	%R29<def> = ISEL %R3<undef>, %R4<kill>, %CR0GT<kill>

where it is relevant that %CC is an alias to %CR0, and that %CR0GT is a
subregister of %CR0. However, for post-RA scheduling, no dependency was added
to prevent the INLINEASM from being scheduled in between the ANDIo8 and the
ISEL (which communicate via the %CR0GT register).

In ScheduleDAGInstrs::addPhysRegDeps, when called for the %CC operand, we'd
iterate over all of its aliases (which include %CC itself and also %CR0), and
look for previously-encountered defs of those registers. We'd find the ANDIo8,
but decide not to add a dependency between the INLINEASM and the ANDIo8 because
both the INLINEASM's def of %CC is dead, and also the ANDIo8 def of %CR0 is
dead. This ignores, however, that ANDIo8 has a non-dead def of %CR0GT, a
subregister of %CR0, and thus a dependency still must exist.

To fix this problem, when calling registerDefIsDead on the SU with the def, we
also check all subregisters for possible non-dead defs, and add the dependency
if any are found.

Fixes PR21742.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223440 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-12-05 01:57:22 +00:00
parent afcbfb40fb
commit d281f1443a
2 changed files with 175 additions and 1 deletions
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8
lib/CodeGen/ScheduleDAGInstrs.cpp
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@ -310,9 +310,15 @@ void ScheduleDAGInstrs::addPhysRegDeps(SUnit *SU, unsigned OperIdx) {
SUnit *DefSU = I->SU;
if (DefSU == &ExitSU)
continue;
auto IsDefDead = [this](SUnit *DefSU, unsigned Reg) {
for (MCSubRegIterator SR(Reg, TRI, true); SR.isValid(); ++SR)
if (!DefSU->getInstr()->registerDefIsDead(*SR))
return false;
return true;
};
if (DefSU != SU &&
(Kind != SDep::Output || !MO.isDead() ||
!DefSU->getInstr()->registerDefIsDead(*Alias))) {
!IsDefDead(DefSU, *Alias))) {
if (Kind == SDep::Anti)
DefSU->addPred(SDep(SU, Kind, /*Reg=*/*Alias));
else {