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Teach BasicAA about noalias parameter attributes, but do it correctly this time.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40711 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Christopher Lamb
2007-08-02 01:18:14 +00:00
parent 8409747efa
commit 406bfa3e21
3 changed files with 58 additions and 1 deletions
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32
lib/Analysis/BasicAliasAnalysis.cpp
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@ -18,6 +18,7 @@
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/ParameterAttributes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
@ -260,6 +261,21 @@ BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
return AliasAnalysis::getModRefInfo(CS, P, Size);
}
static bool isNoAliasArgument(const Argument *Arg) {
const Function *Func = Arg->getParent();
const ParamAttrsList *Attr = Func->getFunctionType()->getParamAttrs();
if (Attr) {
unsigned Idx = 1;
for (Function::const_arg_iterator I = Func->arg_begin(),
E = Func->arg_end(); I != E; ++I, ++Idx) {
if (&(*I) == Arg &&
Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
return true;
}
}
return false;
}
// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
// as array references. Note that this function is heavily tail recursive.
// Hopefully we have a smart C++ compiler. :)
@ -298,10 +314,24 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
if (isa<Argument>(O1)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O2)) return NoAlias;
// If they are two different objects, and one is a noalias argument
// then they do not alias.
if (O1 != O2 && isNoAliasArgument(cast<Argument>(O1)))
return NoAlias;
// Otherwise, nothing is known...
} else if (isa<Argument>(O2)) {
}
if (isa<Argument>(O2)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O1)) return NoAlias;
// If they are two different objects, and one is a noalias argument
// then they do not alias.
if (O1 != O2 && isNoAliasArgument(cast<Argument>(O2)))
return NoAlias;
// Otherwise, nothing is known...
} else if (O1 != O2) {
// If they are two different objects, we know that we have no alias...