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Allow traces to enter nested loops.

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This lets traces include the final iteration of a nested loop above the
center block, and the first iteration of a nested loop below the center
block.

We still don't allow traces to contain backedges, and traces are
truncated where they would leave a loop, as seen from the center block.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161003 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen
2012-07-30 23:15:10 +00:00
parent 9714644a38
commit 1c899cf47c
1 changed files with 29 additions and 14 deletions
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43
lib/CodeGen/MachineTraceMetrics.cpp
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@ -185,6 +185,19 @@ getHeightResources(const MachineBasicBlock *MBB) const {
// DFS, pickTraceSucc() is called in a post-order. // DFS, pickTraceSucc() is called in a post-order.
// //
// We never allow traces that leave loops, but we do allow traces to enter
// nested loops. We also never allow traces to contain back-edges.
//
// This means that a loop header can never appear above the center block of a
// trace, except as the trace head. Below the center block, loop exiting edges
// are banned.
//
// Return true if an edge from the From loop to the To loop is leaving a loop.
// Either of To and From can be null.
static bool isExitingLoop(const MachineLoop *From, const MachineLoop *To) {
return From && !From->contains(To);
}
// MinInstrCountEnsemble - Pick the trace that executes the least number of // MinInstrCountEnsemble - Pick the trace that executes the least number of
// instructions. // instructions.
namespace { namespace {
@ -214,9 +227,6 @@ MinInstrCountEnsemble::pickTracePred(const MachineBasicBlock *MBB) {
for (MachineBasicBlock::const_pred_iterator for (MachineBasicBlock::const_pred_iterator
I = MBB->pred_begin(), E = MBB->pred_end(); I != E; ++I) { I = MBB->pred_begin(), E = MBB->pred_end(); I != E; ++I) {
const MachineBasicBlock *Pred = *I; const MachineBasicBlock *Pred = *I;
// Don't consider predecessors in other loops.
if (getLoopFor(Pred) != CurLoop)
continue;
const MachineTraceMetrics::TraceBlockInfo *PredTBI = const MachineTraceMetrics::TraceBlockInfo *PredTBI =
getDepthResources(Pred); getDepthResources(Pred);
assert(PredTBI && "Predecessor must be visited first"); assert(PredTBI && "Predecessor must be visited first");
@ -242,8 +252,8 @@ MinInstrCountEnsemble::pickTraceSucc(const MachineBasicBlock *MBB) {
// Don't consider back-edges. // Don't consider back-edges.
if (CurLoop && Succ == CurLoop->getHeader()) if (CurLoop && Succ == CurLoop->getHeader())
continue; continue;
// Don't consider successors in other loops. // Don't consider successors exiting CurLoop.
if (getLoopFor(Succ) != CurLoop) if (isExitingLoop(CurLoop, getLoopFor(Succ)))
continue; continue;
const MachineTraceMetrics::TraceBlockInfo *SuccTBI = const MachineTraceMetrics::TraceBlockInfo *SuccTBI =
getHeightResources(Succ); getHeightResources(Succ);
@ -300,11 +310,10 @@ namespace {
struct LoopBounds { struct LoopBounds {
MutableArrayRef<MachineTraceMetrics::TraceBlockInfo> Blocks; MutableArrayRef<MachineTraceMetrics::TraceBlockInfo> Blocks;
const MachineLoopInfo *Loops; const MachineLoopInfo *Loops;
const MachineLoop *CurLoop;
bool Downward; bool Downward;
LoopBounds(MutableArrayRef<MachineTraceMetrics::TraceBlockInfo> blocks, LoopBounds(MutableArrayRef<MachineTraceMetrics::TraceBlockInfo> blocks,
const MachineLoopInfo *loops, const MachineLoop *curloop) const MachineLoopInfo *loops)
: Blocks(blocks), Loops(loops), CurLoop(curloop), Downward(false) {} : Blocks(blocks), Loops(loops), Downward(false) {}
}; };
} }
@ -323,11 +332,17 @@ public:
MachineTraceMetrics::TraceBlockInfo &TBI = LB.Blocks[To->getNumber()]; MachineTraceMetrics::TraceBlockInfo &TBI = LB.Blocks[To->getNumber()];
if (LB.Downward ? TBI.hasValidHeight() : TBI.hasValidDepth()) if (LB.Downward ? TBI.hasValidHeight() : TBI.hasValidDepth())
return false; return false;
// Don't follow CurLoop backedges. // From is null once when To is the trace center block.
if (LB.CurLoop && (LB.Downward ? To : From) == LB.CurLoop->getHeader()) if (!From)
return true;
const MachineLoop *FromLoop = LB.Loops->getLoopFor(From);
if (!FromLoop)
return true;
// Don't follow backedges, don't leave FromLoop when going upwards.
if ((LB.Downward ? To : From) == FromLoop->getHeader())
return false; return false;
// Don't leave CurLoop. // Don't leave FromLoop.
if (LB.Loops->getLoopFor(To) != LB.CurLoop) if (isExitingLoop(FromLoop, LB.Loops->getLoopFor(To)))
return false; return false;
// This is a new block. The PO traversal will compute height/depth // This is a new block. The PO traversal will compute height/depth
// resources, causing us to reject new edges to To. This only works because // resources, causing us to reject new edges to To. This only works because
@ -342,7 +357,7 @@ void MachineTraceMetrics::Ensemble::computeTrace(const MachineBasicBlock *MBB) {
DEBUG(dbgs() << "Computing " << getName() << " trace through BB#" DEBUG(dbgs() << "Computing " << getName() << " trace through BB#"
<< MBB->getNumber() << '\n'); << MBB->getNumber() << '\n');
// Set up loop bounds for the backwards post-order traversal. // Set up loop bounds for the backwards post-order traversal.
LoopBounds Bounds(BlockInfo, CT.Loops, getLoopFor(MBB)); LoopBounds Bounds(BlockInfo, CT.Loops);
// Run an upwards post-order search for the trace start. // Run an upwards post-order search for the trace start.
Bounds.Downward = false; Bounds.Downward = false;
@ -373,7 +388,7 @@ void MachineTraceMetrics::Ensemble::computeTrace(const MachineBasicBlock *MBB) {
// All the successors have been visited, pick the preferred one. // All the successors have been visited, pick the preferred one.
TBI.Succ = pickTraceSucc(*I); TBI.Succ = pickTraceSucc(*I);
DEBUG({ DEBUG({
if (TBI.Pred) if (TBI.Succ)
dbgs() << "BB#" << TBI.Succ->getNumber() << '\n'; dbgs() << "BB#" << TBI.Succ->getNumber() << '\n';
else else
dbgs() << "null\n"; dbgs() << "null\n";