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If we are checking to see if the result of a call aliases a
pointer derived from a local allocation, if the local allocation never escapes, the pointers can't alias. This implements PR2436 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52301 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -317,6 +317,18 @@ static bool isKnownNonNull(const Value *V) {
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return false;
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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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// If this is a local allocation or byval argument, check to see if it
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// escapes.
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if (isa<AllocationInst>(V) ||
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(isa<Argument>(V) && cast<Argument>(V)->hasByValAttr()))
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return !AddressMightEscape(V);
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return false;
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}
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/// isObjectSmallerThan - Return true if we can prove that the object specified
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/// by V is smaller than Size.
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static bool isObjectSmallerThan(const Value *V, unsigned Size,
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@ -393,7 +405,15 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
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(V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
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return NoAlias;
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// If one pointer is the result of a call/invoke and the other is a
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// non-escaping local object, then we know the object couldn't escape to a
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// point where the call could return it.
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if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
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isNonEscapingLocalObject(O2))
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return NoAlias;
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if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
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isNonEscapingLocalObject(O1))
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return NoAlias;
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// If we have two gep instructions with must-alias'ing base pointers, figure
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// out if the indexes to the GEP tell us anything about the derived pointer.
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23
test/Analysis/BasicAA/no-escape-call.ll
Normal file
23
test/Analysis/BasicAA/no-escape-call.ll
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@ -0,0 +1,23 @@
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; RUN: llvm-as < %s | opt -basicaa -gvn -instcombine | llvm-dis | grep {ret i1 true}
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; PR2436
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target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
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target triple = "i386-apple-darwin8"
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define i1 @foo(i32 %i) nounwind {
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entry:
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%arr = alloca [10 x i8*] ; <[10 x i8*]*> [#uses=1]
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%tmp2 = call i8* @getPtr( ) nounwind ; <i8*> [#uses=2]
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%tmp4 = getelementptr [10 x i8*]* %arr, i32 0, i32 %i ; <i8**> [#uses=2]
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store i8* %tmp2, i8** %tmp4, align 4
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%tmp10 = getelementptr i8* %tmp2, i32 10 ; <i8*> [#uses=1]
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store i8 42, i8* %tmp10, align 1
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%tmp14 = load i8** %tmp4, align 4 ; <i8*> [#uses=1]
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%tmp16 = getelementptr i8* %tmp14, i32 10 ; <i8*> [#uses=1]
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%tmp17 = load i8* %tmp16, align 1 ; <i8> [#uses=1]
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%tmp19 = icmp eq i8 %tmp17, 42 ; <i1> [#uses=1]
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ret i1 %tmp19
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}
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declare i8* @getPtr()
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declare void @abort() noreturn nounwind
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