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When checking if an Argument escapes, check if

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the argument is marked nocapture - no need to
analyze the argument if the answer is already
known!

llvm-svn: 61753
This commit is contained in:
Duncan Sands 2009-01-05 21:19:53 +00:00
parent 36e238a4d3
commit 4e1ee2698f
1 changed files with 13 additions and 7 deletions
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20
lib/Analysis/BasicAliasAnalysis.cpp
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@ -35,10 +35,11 @@ using namespace llvm;
// Useful predicates
//===----------------------------------------------------------------------===//
// Determine if an AllocationInst instruction escapes from the function it is
// contained in. If it does not escape, there is no way for another function to
// mod/ref it. We do this by looking at its uses and determining if the uses
// can escape (recursively).
// Determine if a value escapes from the function it is contained in (being
// returned by the function does not count as escaping here). If a value local
// to the function does not escape, there is no way another function can mod/ref
// it. We do this by looking at its uses and determining if they can escape
// (recursively).
static bool AddressMightEscape(const Value *V) {
for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI) {
@ -161,12 +162,17 @@ static bool isNonEscapingLocalObject(const Value *V) {
// If this is a local allocation, check to see if it escapes.
if (isa<AllocationInst>(V) || isNoAliasCall(V))
return !AddressMightEscape(V);
// If this is an argument that corresponds to a byval or noalias argument,
// it can't escape either.
// then it has not escaped before entering the function. Check if it escapes
// inside the function.
if (const Argument *A = dyn_cast<Argument>(V))
if (A->hasByValAttr() || A->hasNoAliasAttr())
if (A->hasByValAttr() || A->hasNoAliasAttr()) {
// Don't bother analyzing arguments already known not to escape.
if (A->hasNoCaptureAttr())
return true;
return !AddressMightEscape(V);
}
return false;
}