[PATCH] D115441: [X86][MS] Add 80bit long double support for Windows

[Phoebe Wang via Phabricator via llvm-commits]

pengfei added a comment.

Hi @rnk , mine is Phoebe#3036. I haven't really used it before. No sure if I invited you correctly, so I try to explain here.

> My comment here refers to the alignment of argument values, not user-declared variables. The frontend controls the alignment of user-declared variables by setting the alloca alignment.

Sure. We have the same goal :)

> GCC and ICC appear to align long double arguments to 4 bytes: https://gcc.godbolt.org/z/PbobWdrPf

Unfortunately, compiler explorer doesn't provide the Windows version ICC. And the alignment on Windows is different from Linux for ICC. Here are my local result:

  > cat ex5.cpp
  void escape(void*);
  void foo(int x, long double d, int y) {
    escape(&x);
    escape(&d);
    escape(&y);
  }
  
  > icl -c ex5.cpp /Qlong-double /Qpc80
  > dumpbin.exe /disasm ex5.obj
  Microsoft (R) COFF/PE Dumper Version 14.29.30133.0
  Copyright (C) Microsoft Corporation.  All rights reserved.
  
  
  Dump of file ex5.obj
  
  File Type: COFF OBJECT
  
  ?foo@@YAXH_TH at Z (void __cdecl foo(int,decltype(auto),int)):
    00000000: 8D 44 24 04        lea         eax,[esp+4]
    00000004: 50                 push        eax
    00000005: E8 00 00 00 00     call        ?escape@@YAXPAX at Z
    0000000A: 8D 44 24 18        lea         eax,[esp+18h]
    0000000E: 50                 push        eax
    0000000F: E8 00 00 00 00     call        ?escape@@YAXPAX at Z
    00000014: 8D 44 24 2C        lea         eax,[esp+2Ch]
    00000018: 50                 push        eax
    00000019: E8 00 00 00 00     call        ?escape@@YAXPAX at Z
    0000001E: 83 C4 0C           add         esp,0Ch
    00000021: C3                 ret
    00000022: 0F 1F 80 00 00 00  nop         dword ptr [eax]
              00
    00000029: 0F 1F 80 00 00 00  nop         dword ptr [eax]
              00
  
    Summary
  
            B7 .drectve
            30 .text

As you can see, the `x` and `d` has 16 bytes distance.
I realized I should have put the result earlier to avoid the ambiguity. Sorry for the inconvenience!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115441/new/

https://reviews.llvm.org/D115441