[PATCH] D116694: [RISCV] Add strictfp support for compares.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/test/CodeGen/RISCV/double-fcmp-strict.ll:205
+; RV64I-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
+; RV64I-NEXT:    call __ledf2 at plt
+; RV64I-NEXT:    slti a0, a0, 1
----------------
Jim wrote:
> craig.topper wrote:
> > Jim wrote:
> > > I am not sure that does the exception raise in `__ledf2` ? 
> > > In GCC, it use `__unorddf2` to check either operands is NaN before `__ledf2`.
> > I'm not seeing `__unorddf2` when I tried testing https://godbolt.org/z/fb7PWaso4
> https://godbolt.org/z/nWbfh9hjx
> Clang extra appended options `-ffp-exception-behavior=strict -Xclang -fexperimental-strict-floating-point` to enable strict floating-point.
> 
> option:  -O3 -march=rv64if -mabi=lp64f -g0  -ffp-exception-behavior=strict -Xclang -fexperimental-strict-floating-point
> 
> ```
>         addi    sp, sp, -16
>         sd      ra, 8(sp)                       # 8-byte Folded Spill
>         call    __gtdf2 at plt                                                              <<< may raise fp exception
>         sgtz    a0, a0
>         ld      ra, 8(sp)                       # 8-byte Folded Reload
>         addi    sp, sp, 16
>         ret
> ```
> 
> option: -O3 -march=rv64ifd -mabi=lp64f -g0 -ffp-exception-behavior=strict -Xclang -fexperimental-strict-floating-point
> 
> 
> ```
>         fmv.d.x ft0, a0
>         fmv.d.x ft1, a1
>         frflags a1
>         flt.d   a0, ft1, ft0
>         fsflags a1
>         feq.d   zero, ft1, ft0
>         ret
> ```
> 
> GCC use `call  __unorddf2` to check either operands is NaN.
Sorry I misunderstood which comparison we were talking about and what you thought the bug was.

I agree this looks like a bug. I'm not how to fix. We probably need to introduce control flow in IR before SelectionDAG to branch over the call to `__ledf2`


Repository:
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  https://reviews.llvm.org/D116694/new/

https://reviews.llvm.org/D116694