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A global variable with internal linkage where all uses are in one function and whose address is never taken is a non-escaping local object and can't alias anything else.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128140 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Anders Carlsson 2011-03-23 02:19:48 +00:00
parent a2f45291e1
commit 90af342061
2 changed files with 52 additions and 0 deletions
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33
lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -57,6 +57,29 @@ static bool isKnownNonNull(const Value *V) {
return false;
}
/// areAllUsesInOneFunction - Return true if all the uses of the given value
/// are in the same function. Note that this returns false if any of the uses
/// are from non-instruction values.
static bool areAllUsesInOneFunction(const Value *V) {
const llvm::Function *Fn = 0;
for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI) {
if (const Instruction *I = dyn_cast<Instruction>(*UI)) {
if (!Fn) {
Fn = I->getParent()->getParent();
continue;
}
if (Fn != I->getParent()->getParent())
return false;
} else
return false;
}
return true;
}
/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
/// object that never escapes from the function.
static bool isNonEscapingLocalObject(const Value *V) {
@ -79,6 +102,16 @@ static bool isNonEscapingLocalObject(const Value *V) {
return true;
return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
}
// If this is an internal global variable that's only used in this function,
// check if it escapes the function.
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
if (GV->hasInternalLinkage() && areAllUsesInOneFunction(GV)) {
return !PointerMayBeCaptured(V, /*ReturnCaptures=*/true,
/*StoreCaptures=*/true);
}
}
return false;
}

19
test/Analysis/BasicAA/non-escaping-local-object.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output < %s |& FileCheck %s
@global = internal global i32 0
declare void @should_not_be_called()
declare i32 @f()
; CHECK: Function: g: 2 pointers, 0 call sites
define void @g(i32* nocapture %p) {
store i32 0, i32* @global
; @global is internal, is only used in this function, and never has its
; address taken so it can't alias p.
; CHECK: NoAlias: i32* %p, i32* @global
store i32 1, i32* %p
%1 = load i32* @global
ret void
}