[all-commits] [llvm/llvm-project] ee5aaa: [RISCV][test] Add additional RUN lines to half-con...

[Alex Bradbury via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: ee5aaa8e6c3f77925ca92f28cb961c0804986dd7
      https://github.com/llvm/llvm-project/commit/ee5aaa8e6c3f77925ca92f28cb961c0804986dd7
  Author: Alex Bradbury <asb at igalia.com>
  Date:   2023-06-30 (Fri, 30 Jun 2023)

  Changed paths:
    M llvm/test/CodeGen/RISCV/half-convert.ll

  Log Message:
  -----------
  [RISCV][test] Add additional RUN lines to half-convert.ll in preparation for D151824

There wasn't previous coverage for rv32id-ilp32, rv64id-lp64,
rv32id-ilp32d, or rv64id-lp64d. This is needed as D151284 fixes a bug
related to the ABI used for libcalls for fp<->fp16 conversion when hard
FP support is present.


  Commit: 5ba40c7be35679a26d7b2c29affaad09aabf5e22
      https://github.com/llvm/llvm-project/commit/5ba40c7be35679a26d7b2c29affaad09aabf5e22
  Author: Alex Bradbury <asb at igalia.com>
  Date:   2023-06-30 (Fri, 30 Jun 2023)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/test/CodeGen/RISCV/calling-conv-half.ll
    M llvm/test/CodeGen/RISCV/copysign-casts.ll
    M llvm/test/CodeGen/RISCV/fp16-promote.ll
    M llvm/test/CodeGen/RISCV/fpclamptosat.ll
    M llvm/test/CodeGen/RISCV/half-convert.ll
    M llvm/test/CodeGen/RISCV/libcall-tail-calls.ll
    M llvm/test/CodeGen/RISCV/rvv/fpclamptosat_vec.ll
    M llvm/test/CodeGen/RISCV/rvv/pr63596.ll

  Log Message:
  -----------
  [RISCV] Custom lower FP_TO_FP16 and FP16_TO_FP to correct ABI of of libcall

As introduced in D99148, RISC-V uses the softPromoteHalf legalisation
for fp16 values without zfh, with logic ensuring that f16 values are
passed in lower bits of FPRs (see D98670) when F or D support is
present. This legalisation produces ISD::FP_TO_FP16 and ISD::FP16_TO_FP
nodes which (as described in ISDOpcodes.h) provide a "semi-softened
interface for dealing with f16 (as an i16)". i.e. the return type of the
FP_TO_FP16 is an integer rather than a float (and the arg of FP16_TO_FP
is an integer). The remainder of the description focuses primarily on
FP_TO_FP16 for ease of explanation.

FP_TO_FP16 is lowered to a libcall to `__truncsfhf2 (float)` or
`__truncdfhf2 (double)`. As of D92241, `_Float16` is used as the return
type of these libcalls if the host compiler accepts `_Float16` in a test
input (i.e. dst_t is set to `_Float16`). `_Float16` is enabled for the
RISC-V target as of D105001 and so the return value should be passed in
an FPR on hard float ABIs.

This patch fixes the ABI issue in what appears to be a minimally
invasive way - leaving the softPromoteHalf logic undisturbed, and
lowering FP_TO_FP16 to an f32-returning libcall, converting its result
to an XLen integer value.

As can be seen in the test changes, the custom lowering for FP16_TO_FP
means the libcall is no longer tail-callable.

Although this patch fixes the issue, there are two open items:
* Redundant fmv.x.w and fmv.w.x pairs are now somtimes produced during
  lowering (not a correctness issue).
* Now coverage for STRICT variants of FP16 conversion opcodes.

Differential Revision: https://reviews.llvm.org/D151284


Compare: https://github.com/llvm/llvm-project/compare/b7e8a55a83bf...5ba40c7be356