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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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128140 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -57,6 +57,29 @@ static bool isKnownNonNull(const Value *V) {
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return false;
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}
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/// areAllUsesInOneFunction - Return true if all the uses of the given value
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/// are in the same function. Note that this returns false if any of the uses
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/// are from non-instruction values.
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static bool areAllUsesInOneFunction(const Value *V) {
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const llvm::Function *Fn = 0;
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for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
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UI != E; ++UI) {
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if (const Instruction *I = dyn_cast<Instruction>(*UI)) {
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if (!Fn) {
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Fn = I->getParent()->getParent();
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continue;
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}
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if (Fn != I->getParent()->getParent())
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return false;
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} else
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return false;
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}
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return true;
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}
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/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
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/// object that never escapes from the function.
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static bool isNonEscapingLocalObject(const Value *V) {
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@ -79,6 +102,16 @@ static bool isNonEscapingLocalObject(const Value *V) {
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return true;
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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}
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// If this is an internal global variable that's only used in this function,
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// check if it escapes the function.
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if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
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if (GV->hasInternalLinkage() && areAllUsesInOneFunction(GV)) {
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return !PointerMayBeCaptured(V, /*ReturnCaptures=*/true,
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/*StoreCaptures=*/true);
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}
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}
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return false;
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}
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19
test/Analysis/BasicAA/non-escaping-local-object.ll
Normal file
19
test/Analysis/BasicAA/non-escaping-local-object.ll
Normal file
@ -0,0 +1,19 @@
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; RUN: opt -basicaa -aa-eval -print-all-alias-modref-info -disable-output < %s |& FileCheck %s
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@global = internal global i32 0
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declare void @should_not_be_called()
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declare i32 @f()
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; CHECK: Function: g: 2 pointers, 0 call sites
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define void @g(i32* nocapture %p) {
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store i32 0, i32* @global
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; @global is internal, is only used in this function, and never has its
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; address taken so it can't alias p.
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; CHECK: NoAlias: i32* %p, i32* @global
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store i32 1, i32* %p
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%1 = load i32* @global
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ret void
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}
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