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speed up BasicAA a bit by implementing a long-standing TODO.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89663 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-11-23 16:44:43 +00:00
parent c46530b6a3
commit b34b82e9d1
1 changed files with 20 additions and 9 deletions
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29
lib/Analysis/BasicAliasAnalysis.cpp
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@ -289,18 +289,29 @@ BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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;
}