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Be more conservative when forming compact regions.

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Apply twice the negative bias on transparent blocks when computing the
compact regions. This excludes loop backedges from the region when only
one of the loop blocks uses the register.

Previously, we would include the backedge in the region if the loop
preheader and the loop latch both used the register, but the loop header
didn't.

When both the header and latch blocks use the register, we still keep it
live on the backedge.

llvm-svn: 136832
This commit is contained in:
Jakob Stoklund Olesen 2011-08-03 23:09:38 +00:00
parent b2c1fe2ccc
commit faae878e65
3 changed files with 8 additions and 3 deletions
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4
lib/CodeGen/RegAllocGreedy.cpp
View File

@ -806,7 +806,9 @@ void RAGreedy::growRegion(GlobalSplitCandidate &Cand) {
if (Cand.PhysReg)
addThroughConstraints(Cand.Intf, NewBlocks);
else
SpillPlacer->addPrefSpill(NewBlocks);
// Provide a strong negative bias on through blocks to prevent unwanted
// liveness on loop backedges.
SpillPlacer->addPrefSpill(NewBlocks, /* Strong= */ true);
AddedTo = ActiveBlocks.size();
// Perhaps iterating can enable more bundles?

4
lib/CodeGen/SpillPlacement.cpp
View File

@ -241,10 +241,12 @@ void SpillPlacement::addConstraints(ArrayRef<BlockConstraint> LiveBlocks) {
}
/// addPrefSpill - Same as addConstraints(PrefSpill)
void SpillPlacement::addPrefSpill(ArrayRef<unsigned> Blocks) {
void SpillPlacement::addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong) {
for (ArrayRef<unsigned>::iterator I = Blocks.begin(), E = Blocks.end();
I != E; ++I) {
float Freq = getBlockFrequency(*I);
if (Strong)
Freq += Freq;
unsigned ib = bundles->getBundle(*I, 0);
unsigned ob = bundles->getBundle(*I, 1);
activate(ib);

3
lib/CodeGen/SpillPlacement.h
View File

@ -107,7 +107,8 @@ public:
/// Entry = Exit = PrefSpill, and ChangesValue = false.
///
/// @param Blocks Array of block numbers that prefer to spill in and out.
void addPrefSpill(ArrayRef<unsigned> Blocks);
/// @param Strong When true, double the negative bias for these blocks.
void addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong);
/// addLinks - Add transparent blocks with the given numbers.
void addLinks(ArrayRef<unsigned> Links);