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Fixed a bug where CFLAA would crash the compiler.

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We would crash if we couldn't locate a Function that either Location's
Value belonged to. Now we just print out a debug message and return 
conservatively.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228901 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
George Burgess IV 2015-02-12 03:07:07 +00:00
parent ffc97a6ae1
commit c571d114ba
2 changed files with 29 additions and 6 deletions
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19
lib/Analysis/CFLAliasAnalysis.cpp
View File

@ -43,6 +43,7 @@
#include "llvm/Pass.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
@ -51,6 +52,8 @@
using namespace llvm;
#define DEBUG_TYPE "cfl-aa"
// Try to go from a Value* to a Function*. Never returns nullptr.
static Optional<Function *> parentFunctionOfValue(Value *);
@ -229,6 +232,7 @@ public:
if (isa<Constant>(LocA.Ptr) && isa<Constant>(LocB.Ptr)) {
return AliasAnalysis::alias(LocA, LocB);
}
AliasResult QueryResult = query(LocA, LocB);
if (QueryResult == MayAlias)
return AliasAnalysis::alias(LocA, LocB);
@ -973,8 +977,10 @@ CFLAliasAnalysis::query(const AliasAnalysis::Location &LocA,
auto MaybeFnA = parentFunctionOfValue(ValA);
auto MaybeFnB = parentFunctionOfValue(ValB);
if (!MaybeFnA.hasValue() && !MaybeFnB.hasValue()) {
llvm_unreachable("Don't know how to extract the parent function "
"from values A or B");
// The only times this is known to happen are when globals + InlineAsm
// are involved
DEBUG(dbgs() << "CFLAA: could not extract parent function information.\n");
return AliasAnalysis::MayAlias;
}
if (MaybeFnA.hasValue()) {
@ -1002,14 +1008,15 @@ CFLAliasAnalysis::query(const AliasAnalysis::Location &LocA,
auto SetB = *MaybeB;
auto AttrsA = Sets.getLink(SetA.Index).Attrs;
auto AttrsB = Sets.getLink(SetB.Index).Attrs;
// Stratified set attributes are used as markets to signify whether a member
// of a StratifiedSet (or a member of a set above the current set) has
// of a StratifiedSet (or a member of a set above the current set) has
// interacted with either arguments or globals. "Interacted with" meaning
// its value may be different depending on the value of an argument or
// its value may be different depending on the value of an argument or
// global. The thought behind this is that, because arguments and globals
// may alias each other, if AttrsA and AttrsB have touched args/globals,
// we must conservatively say that they alias. However, if at least one of
// the sets has no values that could legally be altered by changing the value
// we must conservatively say that they alias. However, if at least one of
// the sets has no values that could legally be altered by changing the value
// of an argument or global, then we don't have to be as conservative.
if (AttrsA.any() && AttrsB.any())
return AliasAnalysis::MayAlias;

16
test/Analysis/CFLAliasAnalysis/asm-global-bugfix.ll Normal file
View File

@ -0,0 +1,16 @@
; Test case for a bug where we would crash when we were requested to report
; whether two values that didn't belong to a function (i.e. two globals, etc)
; aliased.
; RUN: opt < %s -cfl-aa -aa-eval -print-may-aliases -disable-output 2>&1 | FileCheck %s
@G = private unnamed_addr constant [1 x i8] c"\00", align 1
; CHECK: Function: test_no_crash
; CHECK: 1 no alias responses
define void @test_no_crash() #0 {
entry:
call i8* asm "nop", "=r,r"(
i8* getelementptr inbounds ([1 x i8]* @G, i64 0, i64 0))
ret void
}