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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!

llvm-svn: 142558
This commit is contained in:
Nick Lewycky 2011-10-20 00:34:35 +00:00
parent 38661ab3ce
commit 21a67a1454
2 changed files with 19 additions and 6 deletions
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19
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
/// and returns the string in Str. If unsuccessful, it returns false.
bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
uint64_t Offset,
bool StopAtNul) {
uint64_t Offset, bool StopAtNul) {
// If V is NULL then 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
// GEP instruction, then return false because ConstantArray can't occur
// any other way
// any other way.
const User *GEP = 0;
if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(V)) {
GEP = GEPI;
@ -1576,7 +1575,7 @@ bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
return GetConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset,
StopAtNul);
}
// The GEP instruction, constant or instruction, must reference a global
// variable that is a constant and is initialized. The referenced constant
// initializer is the array that we'll use for optimization.
@ -1585,8 +1584,8 @@ bool llvm::GetConstantStringInfo(const Value *V, std::string &Str,
return false;
const Constant *GlobalInit = GV->getInitializer();
// Handle the ConstantAggregateZero case
if (isa<ConstantAggregateZero>(GlobalInit)) {
// Handle the all-zeros case
if (GlobalInit->isNullValue()) {
// This is a degenerate case. The initializer is constant zero so the
// length of the string must be zero.
Str.clear();
@ -1667,6 +1666,14 @@ static uint64_t GetStringLengthH(Value *V, SmallPtrSet<PHINode*, 32> &PHIs) {
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
// GEP instruction, then return unknown.
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]
@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]
@nullstring = constant i8 0
declare i32 @strlen(i8*)
@ -54,3 +55,8 @@ define i1 @test7() {
%ne_null = icmp ne i32 %null_l, 0 ; <i1> [#uses=1]
ret i1 %ne_null
}
define i32 @test8() {
%len = tail call i32 @strlen(i8* @nullstring) nounwind
ret i32 %len
}