instcombine: Migrate memcmp optimizations
This patch migrates the memcmp optimizations from the simplify-libcalls
pass into the instcombine library call simplifier.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167683 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index b5ea46d..805fcbe 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -914,6 +914,51 @@
}
};
+struct MemCmpOpt : public LibCallOptimization {
+ virtual Value *callOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
+ FunctionType *FT = Callee->getFunctionType();
+ if (FT->getNumParams() != 3 || !FT->getParamType(0)->isPointerTy() ||
+ !FT->getParamType(1)->isPointerTy() ||
+ !FT->getReturnType()->isIntegerTy(32))
+ return 0;
+
+ Value *LHS = CI->getArgOperand(0), *RHS = CI->getArgOperand(1);
+
+ if (LHS == RHS) // memcmp(s,s,x) -> 0
+ return Constant::getNullValue(CI->getType());
+
+ // Make sure we have a constant length.
+ ConstantInt *LenC = dyn_cast<ConstantInt>(CI->getArgOperand(2));
+ if (!LenC) return 0;
+ uint64_t Len = LenC->getZExtValue();
+
+ if (Len == 0) // memcmp(s1,s2,0) -> 0
+ return Constant::getNullValue(CI->getType());
+
+ // memcmp(S1,S2,1) -> *(unsigned char*)LHS - *(unsigned char*)RHS
+ if (Len == 1) {
+ Value *LHSV = B.CreateZExt(B.CreateLoad(CastToCStr(LHS, B), "lhsc"),
+ CI->getType(), "lhsv");
+ Value *RHSV = B.CreateZExt(B.CreateLoad(CastToCStr(RHS, B), "rhsc"),
+ CI->getType(), "rhsv");
+ return B.CreateSub(LHSV, RHSV, "chardiff");
+ }
+
+ // Constant folding: memcmp(x, y, l) -> cnst (all arguments are constant)
+ StringRef LHSStr, RHSStr;
+ if (getConstantStringInfo(LHS, LHSStr) &&
+ getConstantStringInfo(RHS, RHSStr)) {
+ // Make sure we're not reading out-of-bounds memory.
+ if (Len > LHSStr.size() || Len > RHSStr.size())
+ return 0;
+ uint64_t Ret = memcmp(LHSStr.data(), RHSStr.data(), Len);
+ return ConstantInt::get(CI->getType(), Ret);
+ }
+
+ return 0;
+ }
+};
+
} // End anonymous namespace.
namespace llvm {
@@ -932,7 +977,7 @@
StpCpyChkOpt StpCpyChk;
StrNCpyChkOpt StrNCpyChk;
- // String and memory library call optimizations.
+ // String library call optimizations.
StrCatOpt StrCat;
StrNCatOpt StrNCat;
StrChrOpt StrChr;
@@ -949,6 +994,9 @@
StrCSpnOpt StrCSpn;
StrStrOpt StrStr;
+ // Memory library call optimizations.
+ MemCmpOpt MemCmp;
+
void initOptimizations();
void addOpt(LibFunc::Func F, LibCallOptimization* Opt);
public:
@@ -972,7 +1020,7 @@
Optimizations["__strncpy_chk"] = &StrNCpyChk;
Optimizations["__stpncpy_chk"] = &StrNCpyChk;
- // String and memory library call optimizations.
+ // String library call optimizations.
addOpt(LibFunc::strcat, &StrCat);
addOpt(LibFunc::strncat, &StrNCat);
addOpt(LibFunc::strchr, &StrChr);
@@ -994,6 +1042,9 @@
addOpt(LibFunc::strspn, &StrSpn);
addOpt(LibFunc::strcspn, &StrCSpn);
addOpt(LibFunc::strstr, &StrStr);
+
+ // Memory library call optimizations.
+ addOpt(LibFunc::memcmp, &MemCmp);
}
Value *LibCallSimplifierImpl::optimizeCall(CallInst *CI) {