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"@string = constant i8 0" is a value i8* string of length zero. Analyze that

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correctly in GetStringLength, fixing PR11181!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142558 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2011-10-20 00:34:35 +00:00
parent 6690bca623
commit 0cd0fee91e
2 changed files with 19 additions and 6 deletions
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17
lib/Analysis/ValueTracking.cpp
View File

@ -1525,8 +1525,7 @@ Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
/// null-terminated C string pointed to by V. If successful, it returns true /// null-terminated C string pointed to by V. If successful, it returns true
/// and returns the string in Str. If unsuccessful, it returns false. /// and returns the string in Str. If unsuccessful, it returns false.
bool llvm::GetConstantStringInfo(const Value *V, std::string &Str, bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
uint64_t Offset, uint64_t Offset, bool StopAtNul) {
bool StopAtNul) {
// If V is NULL then return false; // If V is NULL then return false;
if (V == NULL) return false; if (V == NULL) return false;
@ -1536,7 +1535,7 @@ bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
// If the value is not a GEP instruction nor a constant expression with a // If the value is not a GEP instruction nor a constant expression with a
// GEP instruction, then return false because ConstantArray can't occur // GEP instruction, then return false because ConstantArray can't occur
// any other way // any other way.
const User *GEP = 0; const User *GEP = 0;
if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) { if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
GEP = GEPI; GEP = GEPI;
@ -1585,8 +1584,8 @@ bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
return false; return false;
const Constant *GlobalInit = GV->getInitializer(); const Constant *GlobalInit = GV->getInitializer();
// Handle the ConstantAggregateZero case // Handle the all-zeros case
if (isa<ConstantAggregateZero>(GlobalInit)) { if (GlobalInit->isNullValue()) {
// This is a degenerate case. The initializer is constant zero so the // This is a degenerate case. The initializer is constant zero so the
// length of the string must be zero. // length of the string must be zero.
Str.clear(); Str.clear();
@ -1667,6 +1666,14 @@ static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) {
return Len1; return Len1;
} }
// As a special-case, "@string = constant i8 0" is also a string with zero
// length, not wrapped in a bitcast or GEP.
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
if (GV->isConstant() && GV->hasDefinitiveInitializer())
if (GV->getInitializer()->isNullValue()) return 1;
return 0;
}
// If the value is not a GEP instruction nor a constant expression with a // If the value is not a GEP instruction nor a constant expression with a
// GEP instruction, then return unknown. // GEP instruction, then return unknown.
User *GEP = 0; User *GEP = 0;

6
test/Transforms/SimplifyLibCalls/StrLen.ll
View File

@ -6,6 +6,7 @@ target datalayout = "e-p:32:32"
@hello = constant [6 x i8] c"hello\00" ; <[6 x i8]*> [#uses=3] @hello = constant [6 x i8] c"hello\00" ; <[6 x i8]*> [#uses=3]
@null = constant [1 x i8] zeroinitializer ; <[1 x i8]*> [#uses=3] @null = constant [1 x i8] zeroinitializer ; <[1 x i8]*> [#uses=3]
@null_hello = constant [7 x i8] c"\00hello\00" ; <[7 x i8]*> [#uses=1] @null_hello = constant [7 x i8] c"\00hello\00" ; <[7 x i8]*> [#uses=1]
@nullstring = constant i8 0
declare i32 @strlen(i8*) declare i32 @strlen(i8*)
@ -54,3 +55,8 @@ define i1 @test7() {
%ne_null = icmp ne i32 %null_l, 0 ; <i1> [#uses=1] %ne_null = icmp ne i32 %null_l, 0 ; <i1> [#uses=1]
ret i1 %ne_null ret i1 %ne_null
} }
define i32 @test8() {
%len = tail call i32 @strlen(i8* @nullstring) nounwind
ret i32 %len
}