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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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29
lib/Analysis/BasicAliasAnalysis.cpp
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@ -79,7 +79,12 @@ static bool isKnownNonNull(const Value *V) {
static bool isNonEscapingLocalObject(const Value *V) {
// If this is a local allocation, check to see if it escapes.
if (isa<AllocaInst>(V) || isNoAliasCall(V))
return !PointerMayBeCaptured(V, false);
// Set StoreCaptures to True so that we can assume in our callers that the
// pointer is not the result of a load instruction. Currently
// PointerMayBeCaptured doesn't have any special analysis for the
// StoreCaptures=false case; if it did, our callers could be refined to be
// more precise.
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
// If this is an argument that corresponds to a byval or noalias argument,
// then it has not escaped before entering the function. Check if it escapes
@ -89,7 +94,7 @@ static bool isNonEscapingLocalObject(const Value *V) {
// Don't bother analyzing arguments already known not to escape.
if (A->hasNoCaptureAttr())
return true;
return !PointerMayBeCaptured(V, false);
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
}
return false;
}
@ -683,15 +688,19 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
(V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD)))
return NoAlias;
// If one pointer is the result of a call/invoke and the other is a
// If one pointer is the result of a call/invoke or load and the other is a
// non-escaping local object, then we know the object couldn't escape to a
// point where the call could return it.
if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
isNonEscapingLocalObject(O2) && O1 != O2)
return NoAlias;
if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
isNonEscapingLocalObject(O1) && O1 != O2)
return NoAlias;
// point where the call could return it. The load case works because
// isNonEscapingLocalObject considers all stores to be escapes (it
// passes true for the StoreCaptures argument to PointerMayBeCaptured).
if (O1 != O2) {
if ((isa<CallInst>(O1) || isa<InvokeInst>(O1) || isa<LoadInst>(O1)) &&
isNonEscapingLocalObject(O2))
return NoAlias;
if ((isa<CallInst>(O2) || isa<InvokeInst>(O2) || isa<LoadInst>(O2)) &&
isNonEscapingLocalObject(O1))
return NoAlias;
}
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
std::swap(V1, V2);