instcombine: Migrate strlen optimizations
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
diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index cc03573..658e7c3 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -64,6 +64,26 @@
};
//===----------------------------------------------------------------------===//
+// 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 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 @@
StrCpyOpt StrCpy;
StpCpyOpt StpCpy;
StrNCpyOpt StrNCpy;
+ StrLenOpt StrLen;
void initOptimizations();
public:
@@ -733,6 +776,7 @@
Optimizations["strcpy"] = &StrCpy;
Optimizations["stpcpy"] = &StpCpy;
Optimizations["strncpy"] = &StrNCpy;
+ Optimizations["strlen"] = &StrLen;
}
Value *LibCallSimplifierImpl::optimizeCall(CallInst *CI) {