Implement the NoBuiltin attribute.

The 'nobuiltin' attribute is applied to call sites to indicate that LLVM should
not treat the callee function as a built-in function. I.e., it shouldn't try to
replace that function with different code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175835 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SimplifyLibCalls.cpp

@@ -165,7 +165,7 @@ bool SimplifyLibCalls::runOnFunction(Function &F) {
     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
       // Ignore non-calls.
       CallInst *CI = dyn_cast<CallInst>(I++);
-      if (!CI) continue;
+      if (!CI || CI->hasFnAttr(Attribute::NoBuiltin)) continue;
 
       // Ignore indirect calls and calls to non-external functions.
       Function *Callee = CI->getCalledFunction();