speed up BasicAA a bit by implementing a long-standing TODO.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89663 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index d366a50..af47f20 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -289,18 +289,29 @@
return NoModRef;
// If the pointer is to a locally allocated object that does not escape,
- // then the call can not mod/ref the pointer unless the call takes the
- // argument without capturing it.
+ // then the call can not mod/ref the pointer unless the call takes the pointer
+ // as an argument, and itself doesn't capture it.
if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) {
- bool passedAsArg = false;
- // TODO: Eventually only check 'nocapture' arguments.
+ bool PassedAsArg = false;
+ unsigned ArgNo = 0;
for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
- CI != CE; ++CI)
- if (isa<PointerType>((*CI)->getType()) &&
- alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
- passedAsArg = true;
+ CI != CE; ++CI, ++ArgNo) {
+ // Only look at the no-capture pointer arguments.
+ if (!isa<PointerType>((*CI)->getType()) ||
+ !CS.paramHasAttr(ArgNo+1, Attribute::NoCapture))
+ continue;
+
+ // If this is a no-capture pointer argument, see if we can tell that it
+ // is impossible to alias the pointer we're checking. If not, we have to
+ // assume that the call could touch the pointer, even though it doesn't
+ // escape.
+ if (alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias) {
+ PassedAsArg = true;
+ break;
+ }
+ }
- if (!passedAsArg)
+ if (!PassedAsArg)
return NoModRef;
}