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Change CaptureTracking to pass a Use* instead of a Value* when a value is

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captured. This allows the tracker to look at the specific use, which may be
especially interesting for function calls.

Use this to fix 'nocapture' deduction in FunctionAttrs. The existing one does
not iterate until a fixpoint and does not guarantee that it produces the same
result regardless of iteration order. The new implementation builds up a graph
of how arguments are passed from function to function, and uses a bottom-up walk
on the argument-SCCs to assign nocapture. This gets us nocapture more often, and
does so rather efficiently and independent of iteration order.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147327 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2011-12-28 23:24:21 +00:00
parent da813f4209
commit b48a18903a
6 changed files with 296 additions and 17 deletions
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12
lib/Analysis/CaptureTracking.cpp
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@ -30,8 +30,8 @@ namespace {
bool shouldExplore(Use *U) { return true; }
bool captured(Instruction *I) {
if (isa<ReturnInst>(I) && !ReturnCaptures)
bool captured(Use *U) {
if (isa<ReturnInst>(U->getUser()) && !ReturnCaptures)
return false;
Captured = true;
@ -117,7 +117,7 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
for (CallSite::arg_iterator A = B; A != E; ++A)
if (A->get() == V && !CS.doesNotCapture(A - B))
// The parameter is not marked 'nocapture' - captured.
if (Tracker->captured(I))
if (Tracker->captured(U))
return;
break;
}
@ -130,7 +130,7 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
case Instruction::Store:
if (V == I->getOperand(0))
// Stored the pointer - conservatively assume it may be captured.
if (Tracker->captured(I))
if (Tracker->captured(U))
return;
// Storing to the pointee does not cause the pointer to be captured.
break;
@ -158,12 +158,12 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker) {
break;
// Otherwise, be conservative. There are crazy ways to capture pointers
// using comparisons.
if (Tracker->captured(I))
if (Tracker->captured(U))
return;
break;
default:
// Something else - be conservative and say it is captured.
if (Tracker->captured(I))
if (Tracker->captured(U))
return;
break;
}