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Extend CaptureTracking to indicate when a value is never stored, even

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if it is not ultimately captured. Teach BasicAliasAnalysis that a 
local object address which does not escape and is never stored does
not alias with a value resulting from a load.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89398 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-11-19 21:57:48 +00:00
parent 07ba906413
commit f94b5edc45
5 changed files with 143 additions and 15 deletions
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11
lib/Analysis/CaptureTracking.cpp
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@ -28,8 +28,11 @@ using namespace llvm;
/// by the enclosing function (which is required to exist). This routine can
/// be expensive, so consider caching the results. The boolean ReturnCaptures
/// specifies whether returning the value (or part of it) from the function
/// counts as capturing it or not. The boolean StoreCaptures specified whether
/// storing the value (or part of it) into memory anywhere automatically
/// counts as capturing it or not.
bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
bool llvm::PointerMayBeCaptured(const Value *V,
bool ReturnCaptures, bool StoreCaptures) {
assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
SmallVector<Use*, 16> Worklist;
SmallSet<Use*, 16> Visited;
@ -82,7 +85,11 @@ bool llvm::PointerMayBeCaptured(const Value *V, bool ReturnCaptures) {
break;
case Instruction::Store:
if (V == I->getOperand(0))
// Stored the pointer - it may be captured.
// Stored the pointer - conservatively assume it may be captured.
// TODO: If StoreCaptures is not true, we could do Fancy analysis
// to determine whether this store is not actually an escape point.
// In that case, BasicAliasAnalysis should be updated as well to
// take advantage of this.
return true;
// Storing to the pointee does not cause the pointer to be captured.
break;