[all-commits] [llvm/llvm-project] 47b1f8: [RISCV] Implement isUsedByReturnOnly TargetLowerin...

[Alex Bradbury via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 47b1f8362aa409b591b5e9c8a9ff0e3e1d76ed9c
      https://github.com/llvm/llvm-project/commit/47b1f8362aa409b591b5e9c8a9ff0e3e1d76ed9c
  Author: Alex Bradbury <asb at igalia.com>
  Date:   2022-08-10 (Wed, 10 Aug 2022)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/lib/Target/RISCV/RISCVISelLowering.h
    M llvm/test/CodeGen/RISCV/div.ll
    M llvm/test/CodeGen/RISCV/double-frem.ll
    M llvm/test/CodeGen/RISCV/double-intrinsics.ll
    M llvm/test/CodeGen/RISCV/double-round-conv.ll
    M llvm/test/CodeGen/RISCV/float-intrinsics.ll
    M llvm/test/CodeGen/RISCV/float-round-conv.ll
    M llvm/test/CodeGen/RISCV/fp16-promote.ll
    M llvm/test/CodeGen/RISCV/libcall-tail-calls.ll
    M llvm/test/CodeGen/RISCV/mul.ll
    M llvm/test/CodeGen/RISCV/rem.ll
    M llvm/test/CodeGen/RISCV/srem-lkk.ll
    M llvm/test/CodeGen/RISCV/urem-lkk.ll

  Log Message:
  -----------
  [RISCV] Implement isUsedByReturnOnly TargetLowering hook in order to tailcall more libcalls

Prior to this patch, libcalls inserted by the SelectionDAG legalizer
could never be tailcalled. The eligibility of libcalls for tail calling
is is partly determined by checking TargetLowering::isInTailCallPosition
and comparing the return type of the libcall and the calleer.
isInTailCallPosition in turn calls TargetLowering::isUsedByReturnOnly
(which always returns false if not implemented by the target).

This patch provides a minimal implementation of
TargetLowering::isUsedByReturnOnly - enough to support tail calling
libcalls on hard float ABIs. Soft-float ABIs are left for a follow on
patch. libcall-tail-calls.ll also shows missed opportunities to tail
call integer libcalls, but this is due to issues outside of
the isUsedByReturnOnly hook.

Differential Revision: https://reviews.llvm.org/D131087