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Include loop-carried dependencies when computing instr heights.

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When a trace ends with a back-edge, include PHIs in the loop header in
the height computations. This makes the critical path through a loop
more accurate by including the latencies of the last instructions in the
loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161688 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2012-08-10 20:11:38 +00:00
parent 2a33cec66a
commit 8828c4ccd4
1 changed files with 18 additions and 6 deletions
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24
lib/CodeGen/MachineTraceMetrics.cpp
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@ -931,17 +931,29 @@ computeInstrHeights(const MachineBasicBlock *MBB) {
TBI.CriticalPath = 0;
// Get dependencies from PHIs in the trace successor.
if (TBI.Succ) {
for (MachineBasicBlock::const_iterator
I = TBI.Succ->begin(), E = TBI.Succ->end();
const MachineBasicBlock *Succ = TBI.Succ;
// If MBB is the last block in the trace, and it has a back-edge to the
// loop header, get loop-carried dependencies from PHIs in the header. For
// that purpose, pretend that all the loop header PHIs have height 0.
if (!Succ)
if (const MachineLoop *Loop = getLoopFor(MBB))
if (MBB->isSuccessor(Loop->getHeader()))
Succ = Loop->getHeader();
if (Succ) {
for (MachineBasicBlock::const_iterator I = Succ->begin(), E = Succ->end();
I != E && I->isPHI(); ++I) {
const MachineInstr *PHI = I;
Deps.clear();
getPHIDeps(PHI, Deps, MBB, MTM.MRI);
if (!Deps.empty())
if (pushDepHeight(Deps.front(), PHI, Cycles.lookup(PHI).Height,
Heights, MTM.ItinData, MTM.TII))
if (!Deps.empty()) {
// Loop header PHI heights are all 0.
unsigned Height = TBI.Succ ? Cycles.lookup(PHI).Height : 0;
DEBUG(dbgs() << "pred\t" << Height << '\t' << *PHI);
if (pushDepHeight(Deps.front(), PHI, Height,
Heights, MTM.ItinData, MTM.TII))
addLiveIns(Deps.front().DefMI, Stack);
}
}
}