[PATCH] D50714: [InstCombine] Fold Select with binary op - FP opcodes

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 added inline comments.


================
Comment at: lib/Transforms/InstCombine/InstCombineSelect.cpp:72-73
+    IsEq = true;
+  else if (Pred == FCmpInst::FCMP_ONE)
+    IsEq = false;
+  else
----------------
xbolva00 wrote:
> spatel wrote:
> > xbolva00 wrote:
> > > spatel wrote:
> > > > Did you try testing ONE/UNE in alive-fp?
> > > ```
> > > %A = fcmp one float %x, 0.0
> > > %B = fadd nsz float %x, %z
> > > %C = select i1 %A, float %B, float %y
> > > =>
> > > %C = select i1 %A, float %B, float %z
> > > ----------                                                                      
> > >   %A = fcmp one float %x, 0.0
> > >   %B = fadd nsz float %x, %z
> > >   %C = select %A, float %B, float %y
> > > =>
> > >   %C = select %A, float %B, float %z
> > > 
> > > ERROR: Mismatch in values for float %C                                          
> > > 
> > > Example:
> > > float %x = NaN
> > >    i1 %A = 0x0 (0)
> > > float %z = 0.0640411376953125*(2**-126)
> > > float %B = NaN
> > > float %y = 1.00048828125*(2**1)
> > > source: 1.00048828125*(2**1)
> > > target: 0.0640411376953125*(2**-126)
> > > 
> > > xbolva00 at xbolva00:~/alive-nj$ ./run.py                               
> > > [Reading from terminal...]
> > > %A = fcmp une float %x, 0.0
> > > %B = fadd nsz float %x, %z
> > > %C = select i1 %A, float %B, float %y
> > > =>
> > > %C = select i1 %A, float %B, float %z
> > > ----------                                                                      
> > >   %A = fcmp une float %x, 0.0
> > >   %B = fadd nsz float %x, %z
> > >   %C = select %A, float %B, float %y
> > > =>
> > >   %C = select %A, float %B, float %z
> > > 
> > > ERROR: Mismatch in values for float %C                                          
> > > 
> > > Example:
> > > float %x = = +0.0
> > >    i1 %A = 0x0 (0)
> > > float %z = NaN
> > > float %B = NaN
> > > float %y = 0.0000002384185791015625*(2**-126)
> > > source: 0.0000002384185791015625*(2**-126)
> > > target: NaN
> > > 
> > > ```
> > I think you want these tests to use -0.0 because that's the identity constant for fadd.
> ```
> %A = fcmp one float %x, -0.0
> %B = fadd nsz float %x, %z
> %C = select i1 %A, float %B, float %y
> =>
> %C = select i1 %A, float %B, float %z
> ----------                                                                      
>   %A = fcmp one float %x, -0.0
>   %B = fadd nsz float %x, %z
>   %C = select %A, float %B, float %y
> =>
>   %C = select %A, float %B, float %z
> 
> ERROR: Mismatch in values for float %C                                          
> 
> Example:
> float %x = +0.0
>    i1 %A = 0x0 (0)
> float %z = -0.504963397979736328125*(2**-126)
> float %B = -0.504963397979736328125*(2**-126)
> float %y = 1.5*(2**-125)
> source: 1.5*(2**-125)
> target: -0.504963397979736328125*(2**-126)
> 
> %A = fcmp une float %x, -0.0
> %B = fadd nsz float %x, %z
> %C = select i1 %A, float %B, float %y
> =>
> %C = select i1 %A, float %B, float %z
> ----------                                                                      
>   %A = fcmp une float %x, -0.0
>   %B = fadd nsz float %x, %z
>   %C = select %A, float %B, float %y
> =>
>   %C = select %A, float %B, float %z
> 
> ERROR: Mismatch in values for float %C                                          
> 
> Example:
> float %x = +0.0
>    i1 %A = 0x0 (0)
> float %z = +oo
> float %B = +oo
> float %y = -0.03125*(2**-126)
> source: -0.03125*(2**-126)
> target: +oo
> 
> ```
Ok.

```

%A = fcmp une float %x, -0.0
%B = fadd nsz float %x, %z
%C = select i1 %A, float %y, float %B
=>
%C = select i1 %A, float %y, float %z
----------                                                                      
  %A = fcmp une float %x, -0.0
  %B = fadd nsz float %x, %z
  %C = select %A, float %y, float %B
=>
  %C = select %A, float %y, float %z

Done: 1                                                                         
Optimization is correct
```


https://reviews.llvm.org/D50714