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Added special handling for inttoptr in CFLAA. 

We now treat pointers given to ptrtoint and pointers retrieved from
inttoptr as similar to arguments or globals (can alias anything, etc.)

This solves some of the problems we were having with giving incorrect
results.

llvm-svn: 231741
This commit is contained in:
George Burgess IV 2015-03-10 02:40:06 +00:00
parent a28d91d81b
commit b54a8d62a4
2 changed files with 95 additions and 10 deletions
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32
llvm/lib/Analysis/CFLAliasAnalysis.cpp
View File

@ -85,11 +85,13 @@ typedef unsigned StratifiedAttr;
LLVM_CONSTEXPR unsigned MaxStratifiedAttrIndex = NumStratifiedAttrs;
LLVM_CONSTEXPR unsigned AttrAllIndex = 0;
LLVM_CONSTEXPR unsigned AttrGlobalIndex = 1;
LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 2;
LLVM_CONSTEXPR unsigned AttrUnknownIndex = 2;
LLVM_CONSTEXPR unsigned AttrFirstArgIndex = 3;
LLVM_CONSTEXPR unsigned AttrLastArgIndex = MaxStratifiedAttrIndex;
LLVM_CONSTEXPR unsigned AttrMaxNumArgs = AttrLastArgIndex - AttrFirstArgIndex;
LLVM_CONSTEXPR StratifiedAttr AttrNone = 0;
LLVM_CONSTEXPR StratifiedAttr AttrUnknown = 1 << AttrUnknownIndex;
LLVM_CONSTEXPR StratifiedAttr AttrAll = ~AttrNone;
// \brief StratifiedSets call for knowledge of "direction", so this is how we
@ -263,6 +265,16 @@ public:
llvm_unreachable("Unsupported instruction encountered");
}
void visitPtrToIntInst(PtrToIntInst &Inst) {
auto *Ptr = Inst.getOperand(0);
Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
}
void visitIntToPtrInst(IntToPtrInst &Inst) {
auto *Ptr = &Inst;
Output.push_back(Edge(Ptr, Ptr, EdgeType::Assign, AttrUnknown));
}
void visitCastInst(CastInst &Inst) {
Output.push_back(Edge(&Inst, Inst.getOperand(0), EdgeType::Assign,
AttrNone));
@ -931,16 +943,16 @@ static FunctionInfo buildSetsFrom(CFLAliasAnalysis &Analysis, Function *Fn) {
break;
}
if (Added) {
auto Aliasing = Weight.second;
if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
Aliasing.set(*MaybeCurIndex);
if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
Aliasing.set(*MaybeOtherIndex);
Builder.noteAttributes(CurValue, Aliasing);
Builder.noteAttributes(OtherValue, Aliasing);
auto Aliasing = Weight.second;
if (auto MaybeCurIndex = valueToAttrIndex(CurValue))
Aliasing.set(*MaybeCurIndex);
if (auto MaybeOtherIndex = valueToAttrIndex(OtherValue))
Aliasing.set(*MaybeOtherIndex);
Builder.noteAttributes(CurValue, Aliasing);
Builder.noteAttributes(OtherValue, Aliasing);
if (Added)
Worklist.push_back(OtherNode);
}
}
}
}

73
llvm/test/Analysis/CFLAliasAnalysis/branch-alias.ll Normal file
View File

@ -0,0 +1,73 @@
; Makes sure that we give up on some pathological cases with inttoptr/ptrtoint
;
; @ptr_test was generated from the following C code:
; void ptr_test() {
; int* A;
; unsigned long RefCopy = 0;
; for (int i = 0; i < 8*sizeof(&A); ++i) {
; if ((unsigned long)&A & (1UL << i))
; RefCopy |= 1UL << i;
; }
;
; int** AliasA1 = (int**)RefCopy;
; int* ShouldAliasA = *AliasA1;
; }
; RUN: opt < %s -cfl-aa -aa-eval -print-may-aliases -disable-output 2>&1 | FileCheck %s
; CHECK: Function: ptr_test
define void @ptr_test() #0 {
; CHECK: MayAlias: i32** %A, i32** %ShouldAliasA
; CHECK-NOT: %AliasA1
entry:
%A = alloca i32*, align 8
%RefCopy = alloca i64, align 8
%i = alloca i32, align 4
%AliasA1 = alloca i32**, align 8
%ShouldAliasA = alloca i32*, align 8
store i64 0, i64* %RefCopy, align 8
store i32 0, i32* %i, align 4
br label %for.cond
for.cond: ; preds = %for.inc, %entry
%0 = load i32, i32* %i, align 4
%conv = sext i32 %0 to i64
%cmp = icmp ult i64 %conv, 64
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %for.cond
%1 = ptrtoint i32** %A to i64
%2 = load i32, i32* %i, align 4
%sh_prom = zext i32 %2 to i64
%shl = shl i64 1, %sh_prom
%and = and i64 %1, %shl
%tobool = icmp ne i64 %and, 0
br i1 %tobool, label %if.then, label %if.end
if.then: ; preds = %for.body
%3 = load i32, i32* %i, align 4
%sh_prom2 = zext i32 %3 to i64
%shl3 = shl i64 1, %sh_prom2
%4 = load i64, i64* %RefCopy, align 8
%or = or i64 %4, %shl3
store i64 %or, i64* %RefCopy, align 8
br label %if.end
if.end: ; preds = %if.then, %for.body
br label %for.inc
for.inc: ; preds = %if.end
%5 = load i32, i32* %i, align 4
%inc = add nsw i32 %5, 1
store i32 %inc, i32* %i, align 4
br label %for.cond
for.end: ; preds = %for.cond
%6 = load i64, i64* %RefCopy, align 8
%7 = inttoptr i64 %6 to i32**
store i32** %7, i32*** %AliasA1, align 8
%8 = load i32**, i32*** %AliasA1, align 8
%9 = load i32*, i32** %8, align 8
store i32* %9, i32** %ShouldAliasA, align 8
ret void
}