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Optimize reserved register coalescing.

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Reserved registers don't have proper live ranges, their LiveInterval
simply has a snippet of liveness for each def.  Virtual registers with a
single value that is a copy of a reserved register (typically %esp) can
be coalesced with the reserved register if the live range doesn't
overlap any reserved register defs.

When coalescing with a reserved register, don't modify the reserved
register live range.  Just leave it as a bunch of dead defs.  This
eliminates quadratic coalescer behavior in i386 functions with many
function calls.

PR11699

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147726 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2012-01-07 07:39:50 +00:00
parent 4281e20aab
commit 34786a3ad7
1 changed files with 25 additions and 0 deletions
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25
lib/CodeGen/RegisterCoalescer.cpp
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@ -1431,6 +1431,31 @@ bool RegisterCoalescer::JoinIntervals(CoalescerPair &CP) {
// than the full interfeence check below. We allow overlapping live ranges
// only when one is a copy of the other.
if (CP.isPhys()) {
// Optimization for reserved registers like ESP.
// We can only merge with a reserved physreg if RHS has a single value that
// is a copy of CP.DstReg(). The live range of the reserved register will
// look like a set of dead defs - we don't properly track the live range of
// reserved registers.
if (RegClassInfo.isReserved(CP.getDstReg())) {
assert(CP.isFlipped() && RHS.containsOneValue() &&
"Invalid join with reserved register");
// Deny any overlapping intervals. This depends on all the reserved
// register live ranges to look like dead defs.
for (const unsigned *AS = TRI->getOverlaps(CP.getDstReg()); *AS; ++AS) {
if (!LIS->hasInterval(*AS))
continue;
if (RHS.overlaps(LIS->getInterval(*AS))) {
DEBUG(dbgs() << "\t\tInterference: " << PrintReg(*AS, TRI) << '\n');
return false;
}
}
// Skip any value computations, we are not adding new values to the
// reserved register. Also skip merging the live ranges, the reserved
// register live range doesn't need to be accurate as long as all the
// defs are there.
return true;
}
for (const unsigned *AS = TRI->getAliasSet(CP.getDstReg()); *AS; ++AS){
if (!LIS->hasInterval(*AS))
continue;