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simplify-libcalls: fold strstr(a, b) == a -> strncmp(a, b, strlen(b)) == 0

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106047 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2010-06-15 21:34:25 +00:00
parent 2bbaf4d06e
commit 386e918438
4 changed files with 72 additions and 0 deletions
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31
lib/Transforms/Scalar/SimplifyLibCalls.cpp
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@@ -92,6 +92,20 @@ static bool IsOnlyUsedInZeroEqualityComparison(Value *V) {
return true;
}
/// IsOnlyUsedInEqualityComparison - Return true if it is only used in equality
/// comparisons with With.
static bool IsOnlyUsedInEqualityComparison(Value *V, Value *With) {
for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI) {
if (ICmpInst *IC = dyn_cast<ICmpInst>(*UI))
if (IC->isEquality() && IC->getOperand(1) == With)
continue;
// Unknown instruction.
return false;
}
return true;
}
//===----------------------------------------------------------------------===//
// String and Memory LibCall Optimizations
//===----------------------------------------------------------------------===//
@@ -503,6 +517,23 @@ struct StrStrOpt : public LibCallOptimization {
if (CI->getOperand(1) == CI->getOperand(2))
return B.CreateBitCast(CI->getOperand(1), CI->getType());
// fold strstr(a, b) == a -> strncmp(a, b, strlen(b)) == 0
if (TD && IsOnlyUsedInEqualityComparison(CI, CI->getOperand(1))) {
Value *StrLen = EmitStrLen(CI->getOperand(2), B, TD);
Value *StrNCmp = EmitStrNCmp(CI->getOperand(1), CI->getOperand(2),
StrLen, B, TD);
for (Value::use_iterator UI = CI->use_begin(), UE = CI->use_end();
UI != UE; ) {
ICmpInst *Old = cast<ICmpInst>(UI++);
Value *Cmp = B.CreateICmp(Old->getPredicate(), StrNCmp,
ConstantInt::getNullValue(StrNCmp->getType()),
"cmp");
Old->replaceAllUsesWith(Cmp);
Old->eraseFromParent();
}
return CI;
}
// See if either input string is a constant string.
std::string SearchStr, ToFindStr;
bool HasStr1 = GetConstantStringInfo(CI->getOperand(1), SearchStr);