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CaptureTracking: Plug a loophole in the "too many uses" heuristic. 

The heuristic was added to avoid spending too much compile time A specially
crafted test case (PR17461, PR16474) with many uses on a select or bitcast
instruction can still trigger the slow case. Add a check for that case.

This only affects compile time, don't have a good way to test it.

llvm-svn: 191896
This commit is contained in:
Benjamin Kramer 2013-10-03 13:24:02 +00:00
parent 0d17013cb7
commit d2757ba1be
1 changed files with 6 additions and 0 deletions
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6
llvm/lib/Analysis/CaptureTracking.cpp
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@ -146,8 +146,14 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
case Instruction::PHI: case Instruction::PHI:
case Instruction::Select: case Instruction::Select:
// The original value is not captured via this if the new value isn't. // The original value is not captured via this if the new value isn't.
Count = 0;
for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end(); for (Instruction::use_iterator UI = I->use_begin(), UE = I->use_end();
UI != UE; ++UI) { UI != UE; ++UI) {
// If there are lots of uses, conservatively say that the value
// is captured to avoid taking too much compile time.
if (Count++ >= Threshold)
return Tracker->tooManyUses();
Use *U = &UI.getUse(); Use *U = &UI.getUse();
if (Visited.insert(U)) if (Visited.insert(U))
if (Tracker->shouldExplore(U)) if (Tracker->shouldExplore(U))