[PATCH] D122090: [PPCISelLowering] Avoid emitting calls to __multi3, __muloti4

[Aaron Puchert via Phabricator via llvm-commits]

aaronpuchert added a comment.

In D122090#3394964 <https://reviews.llvm.org/D122090#3394964>, @aaronpuchert wrote:

> I was also wondering if we could block the overflow intrinsics only if `Subtarget.getTargetTriple().isGNUEnvironment()` is true, but we can also discuss this separately.

I see that @craig.topper suggested something similar in D109385 <https://reviews.llvm.org/D109385>.

On the Clang side, we have in `clang::driver::ToolChain`:

  enum RuntimeLibType {
    RLT_CompilerRT,
    RLT_Libgcc
  };

and then `virtual RuntimeLibType GetDefaultRuntimeLibType() const`. Going through the overrides (`git grep -A3 GetDefaultRuntimeLibType clang/lib/Driver/ clang/include/clang/Driver/`), it seems that compiler-rt is the default on AIX, BareMetal, Darwin, Fuchsia, Android Linux, OpenBSD, VE, and WebAssembly. But it's just the default, there could still be a `--rtlib=` command line argument. And since the backend is using the builtin even in cases where the original code didn't use it, we have to be very careful.

An alternative is to pass on the `--rtlib=` argument to the backend (or put it into metadata). At least I think the backend currently doesn't know about the runtime library being used.


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