[llvm-commits] [llvm] r142558 - in /llvm/trunk: lib/Analysis/ValueTracking.cpp test/Transforms/SimplifyLibCalls/StrLen.ll
Nick Lewycky
nicholas at mxc.ca
Wed Oct 19 17:34:35 PDT 2011
Author: nicholas
Date: Wed Oct 19 19:34:35 2011
New Revision: 142558
URL: http://llvm.org/viewvc/llvm-project?rev=142558&view=rev
Log:
"@string = constant i8 0" is a value i8* string of length zero. Analyze that
correctly in GetStringLength, fixing PR11181!
Modified:
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Transforms/SimplifyLibCalls/StrLen.ll
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=142558&r1=142557&r2=142558&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Wed Oct 19 19:34:35 2011
@@ -1525,8 +1525,7 @@
/// 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 @@
// 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 @@
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 @@
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 @@
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;
Modified: llvm/trunk/test/Transforms/SimplifyLibCalls/StrLen.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyLibCalls/StrLen.ll?rev=142558&r1=142557&r2=142558&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyLibCalls/StrLen.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyLibCalls/StrLen.ll Wed Oct 19 19:34:35 2011
@@ -6,6 +6,7 @@
@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]
+ at nullstring = constant i8 0
declare i32 @strlen(i8*)
@@ -54,3 +55,8 @@
%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
+}
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