Teach SimplifyLibCalls to fold memcmp calls with constant arguments.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86141 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/SimplifyLibCalls.cpp b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
index 575c93b..ecca3c7 100644
--- a/lib/Transforms/Scalar/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Scalar/SimplifyLibCalls.cpp
@@ -955,6 +955,17 @@
return B.CreateZExt(B.CreateXor(LHSV, RHSV, "shortdiff"), CI->getType());
}
+ // Constant folding: memcmp(x, y, l) -> cnst (all arguments are constant)
+ std::string LHSStr, RHSStr;
+ if (GetConstantStringInfo(LHS, LHSStr) &&
+ GetConstantStringInfo(RHS, RHSStr)) {
+ // Make sure we're not reading out-of-bounds memory.
+ if (Len > LHSStr.length() || Len > RHSStr.length())
+ return 0;
+ uint64_t Ret = memcmp(LHSStr.data(), RHSStr.data(), Len);
+ return ConstantInt::get(CI->getType(), Ret);
+ }
+
return 0;
}
};
@@ -2479,10 +2490,6 @@
// lround, lroundf, lroundl:
// * lround(cnst) -> cnst'
//
-// memcmp:
-// * memcmp(x,y,l) -> cnst
-// (if all arguments are constant and strlen(x) <= l and strlen(y) <= l)
-//
// pow, powf, powl:
// * pow(exp(x),y) -> exp(x*y)
// * pow(sqrt(x),y) -> pow(x,y*0.5)