Tail calls and portability

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1

I have been working on adding proper tail (via become) to rustc. I was able to make them work (some parts of the type checker aren’t implemented yet). However, I ran into an LLVM-related problem.

LLVM claims to support proper tail calls when fastcc is used — but only on i386, x86-64 and PowerPC. Is this accurate? Will proper tail calls be supported on WebAssembly? Are they supported on ARM? AArch64? Other backends?

2

As a general “good practice", you should answer to your own thread you started this morning instead of starting a new one with little difference: http://lists.llvm.org/pipermail/llvm-dev/2017-January/108678.html

+CC WebAssembly folks to make sure they don’t miss this question.

3

The current version of the WebAssembly ISA doesn’t support tail calls. It is likely that support will be added in future versions.

Dan

4

Note that tail calls on PowerPC can run into the TOC-restoration issue
for non-PIC calls.

Joerg

5

There is some support for tail calls for MIPS, but it is not enabled by default yet.

Thanks,
Simon

6

Hexagon uses tail calls in the right circumstances, but it ignores musttail.

-Krzysztof