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Rename isEarlierInSameTrace to isUsefulDominator.

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In very rare cases caused by irreducible control flow, the dominating
block can have the same trace head without actually being part of the
trace.

As long as such a dominator still has valid instruction depths, it is OK
to use it for computing instruction depths.

Rename the function to avoid lying, and add a check that instruction
depths are computed for the dominator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176668 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen
2013-03-07 23:55:49 +00:00
parent 11687d4982
commit 6ffcd5efe1
2 changed files with 20 additions and 7 deletions
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23
include/llvm/CodeGen/MachineTraceMetrics.h
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@@ -165,12 +165,25 @@ public:
/// Invalidate height resources when a block below this one has changed. /// Invalidate height resources when a block below this one has changed.
void invalidateHeight() { InstrHeight = ~0u; HasValidInstrHeights = false; } void invalidateHeight() { InstrHeight = ~0u; HasValidInstrHeights = false; }
/// Determine if this block belongs to the same trace as TBI and comes /// Assuming that this is a dominator of TBI, determine if it contains
/// before it in the trace. /// useful instruction depths. A dominating block can be above the current
/// trace head, and any dependencies from such a far away dominator are not
/// expected to affect the critical path.
///
/// Also returns true when TBI == this. /// Also returns true when TBI == this.
bool isEarlierInSameTrace(const TraceBlockInfo &TBI) const { bool isUsefulDominator(const TraceBlockInfo &TBI) const {
return hasValidDepth() && TBI.hasValidDepth() && // The trace for TBI may not even be calculated yet.
Head == TBI.Head && InstrDepth <= TBI.InstrDepth; if (!hasValidDepth() || !TBI.hasValidDepth())
return false;
// Instruction depths are only comparable if the traces share a head.
if (Head != TBI.Head)
return false;
// It is almost always the case that TBI belongs to the same trace as
// this block, but rare convoluted cases involving irreducible control
// flow, a dominator may share a trace head without actually being on the
// same trace as TBI. This is not a big problem as long as it doesn't
// increase the instruction depth.
return HasValidInstrDepths && InstrDepth <= TBI.InstrDepth;
} }
// Data-dependency-related information. Per-instruction depth and height // Data-dependency-related information. Per-instruction depth and height

4
lib/CodeGen/MachineTraceMetrics.cpp
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@@ -677,7 +677,7 @@ computeCrossBlockCriticalPath(const TraceBlockInfo &TBI) {
const MachineInstr *DefMI = MTM.MRI->getVRegDef(LIR.Reg); const MachineInstr *DefMI = MTM.MRI->getVRegDef(LIR.Reg);
// Ignore dependencies outside the current trace. // Ignore dependencies outside the current trace.
const TraceBlockInfo &DefTBI = BlockInfo[DefMI->getParent()->getNumber()]; const TraceBlockInfo &DefTBI = BlockInfo[DefMI->getParent()->getNumber()];
if (!DefTBI.isEarlierInSameTrace(TBI)) if (!DefTBI.isUsefulDominator(TBI))
continue; continue;
unsigned Len = LIR.Height + Cycles[DefMI].Depth; unsigned Len = LIR.Height + Cycles[DefMI].Depth;
MaxLen = std::max(MaxLen, Len); MaxLen = std::max(MaxLen, Len);
@@ -740,7 +740,7 @@ computeInstrDepths(const MachineBasicBlock *MBB) {
const TraceBlockInfo&DepTBI = const TraceBlockInfo&DepTBI =
BlockInfo[Dep.DefMI->getParent()->getNumber()]; BlockInfo[Dep.DefMI->getParent()->getNumber()];
// Ignore dependencies from outside the current trace. // Ignore dependencies from outside the current trace.
if (!DepTBI.isEarlierInSameTrace(TBI)) if (!DepTBI.isUsefulDominator(TBI))
continue; continue;
assert(DepTBI.HasValidInstrDepths && "Inconsistent dependency"); assert(DepTBI.HasValidInstrDepths && "Inconsistent dependency");
unsigned DepCycle = Cycles.lookup(Dep.DefMI).Depth; unsigned DepCycle = Cycles.lookup(Dep.DefMI).Depth;