[PATCH] D123198: [LibCalls] Add argument extension attributes to more functions.

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa added a comment.

It seems that the failing test case (Transforms/InstCombine/pr39177.ll) is a bit peculiar in that it contains an fwrite *alias*:

  fwrite = alias i64 (i8*, i64, i64, %struct._IO_FILE*), i64 (i8*, i64, i64, %struct._IO_FILE*)* @__fwrite_alias

It defines the @__fwrite_alias() function, and then has a foo() function containing a call to @fprintf() which SimplifyLibCalls is trying to replace with a call to fwrite(). This is when it crashes because of a nullptr as discovered by the sanitizer.

I am not sure what the idea is here with having an fwrite alias, but it is clear that BuildLibCalls is getting confused:

   FunctionCallee llvm::getOrInsertLibFunc(Module *M, const TargetLibraryInfo &TLI,
                                          LibFunc TheLibFunc, FunctionType *T,
                                          AttributeList AttributeList) {
    assert(TLI.has(TheLibFunc) &&
           "Creating call to non-existing library function.");
    StringRef Name = TLI.getName(TheLibFunc);
  =>FunctionCallee C = M->getOrInsertFunction(Name, T, AttributeList);

at this point M returns the alias:

  (gdb) p C.Callee->dump()
  @fwrite = alias i64 (i8*, i64, i64, %struct._IO_FILE*), i64 (i8*, i64, i64, %struct._IO_FILE*)* @__fwrite_alias

This is a GlobalAlias and not a Function, which is why getFunction() returned nullptr:

  Function &F = *M->getFunction(Name);

Looking at the test case, it seems to be valid to write your own fwrite and expect the compiler use it as a replacement for the standard fwrite call..? I guess this means that getOrInsertLibFunc() should also be able to handle a GlobalAlias?



================
Comment at: llvm/include/llvm/Transforms/Utils/BuildLibCalls.h:46
+                               Type *RetTy, ArgsTy... Args) {
+    SmallVector<Type*, sizeof...(ArgsTy)> ArgTys{Args...};
+    return getOrInsertLibFunc(M, TLI, TheLibFunc,
----------------
MaskRay wrote:
> Consider using a plain array.
Do you have anything special in mind? This was copied from getOrInsertFunction().


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https://reviews.llvm.org/D123198