fix Issue 21526 - x87 not rounding to precision on assignment on some…

[WalterBright]

… platforms

The comment in the code explains it. Maybe @9il can provide the test values?

[dlang-bot]

Thanks for your pull request, @WalterBright!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21526	normal	x87 not rounding to precision on assignment on some platforms

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#12102"

[ibuclaw]

Does this also fix https://issues.dlang.org/show_bug.cgi?id=21376?

[WalterBright]

Does this also fix https://issues.dlang.org/show_bug.cgi?id=21376?

No.

[WalterBright]

Can someone with the Azure setup let me know what code is being generated for the f21526 function in mars1.d?

[MoonlightSentinel]

Can someone with the Azure setup let me know what code is being generated for the f21526 function in mars1.d?

Disassembly of section .text:

00000000 <__D5mars16f21256FddZd>:
   0:	c8 08 00 00          	enter  $0x8,$0x0
   4:	dd 45 10             	fldl   0x10(%ebp)
   7:	dc 45 08             	faddl  0x8(%ebp)
   a:	dd 5d f8             	fstpl  -0x8(%ebp)
   d:	dd 45 f8             	fldl   -0x8(%ebp)
  10:	c9                   	leave  
  11:	c2 10 00             	ret    $0x10

mars1.txt

[WalterBright]

Thank you, @MoonlightSentinel
And that's what the generated code should be (see the store and reload).

[WalterBright]

With some more investigation, I was able to duplicate the problem. Unfortunately, I cannot get the x87 to always produce the same value as XMM. But this change still gets it to do a write/read, which improves things.