Extend CaptureTracking to indicate when a value is never stored, even
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
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index b8d69f4..66bb439 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -79,7 +79,12 @@
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 @@
// 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 @@
(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);