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instcombine: Migrate strlen optimizations

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This patch migrates the strlen optimizations from the simplify-libcalls
pass into the instcombine library call simplifier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167103 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Meador Inge
2012-10-31 03:33:06 +00:00
parent a0885fb882
commit 57cfd71f88
5 changed files with 160 additions and 106 deletions
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44
lib/Transforms/Utils/SimplifyLibCalls.cpp
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@ -63,6 +63,26 @@ public:
}
};
//===----------------------------------------------------------------------===//
// Helper Functions
//===----------------------------------------------------------------------===//
/// isOnlyUsedInZeroEqualityComparison - Return true if it only matters that the
/// value is equal or not-equal to zero.
static bool isOnlyUsedInZeroEqualityComparison(Value *V) {
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())
if (Constant *C = dyn_cast<Constant>(IC->getOperand(1)))
if (C->isNullValue())
continue;
// Unknown instruction.
return false;
}
return true;
}
//===----------------------------------------------------------------------===//
// Fortified Library Call Optimizations
//===----------------------------------------------------------------------===//
@ -675,6 +695,28 @@ struct StrNCpyOpt : public LibCallOptimization {
}
};
struct StrLenOpt : public LibCallOptimization {
virtual Value *callOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
FunctionType *FT = Callee->getFunctionType();
if (FT->getNumParams() != 1 ||
FT->getParamType(0) != B.getInt8PtrTy() ||
!FT->getReturnType()->isIntegerTy())
return 0;
Value *Src = CI->getArgOperand(0);
// Constant folding: strlen("xyz") -> 3
if (uint64_t Len = GetStringLength(Src))
return ConstantInt::get(CI->getType(), Len-1);
// strlen(x) != 0 --> *x != 0
// strlen(x) == 0 --> *x == 0
if (isOnlyUsedInZeroEqualityComparison(CI))
return B.CreateZExt(B.CreateLoad(Src, "strlenfirst"), CI->getType());
return 0;
}
};
} // End anonymous namespace.
namespace llvm {
@ -702,6 +744,7 @@ class LibCallSimplifierImpl {
StrCpyOpt StrCpy;
StpCpyOpt StpCpy;
StrNCpyOpt StrNCpy;
StrLenOpt StrLen;
void initOptimizations();
public:
@ -733,6 +776,7 @@ void LibCallSimplifierImpl::initOptimizations() {
Optimizations["strcpy"] = &StrCpy;
Optimizations["stpcpy"] = &StpCpy;
Optimizations["strncpy"] = &StrNCpy;
Optimizations["strlen"] = &StrLen;
}
Value *LibCallSimplifierImpl::optimizeCall(CallInst *CI) {