Lot of -Wstrict-aliasing warnings

[orbea]

OS: Gentoo
GLideN64: f4b0755
compiler: gcc version 13.3.1 20240614 (Gentoo 13.3.1_p20240614 p17)

When compiling GLideN64 there are a lot of -Wstrict-aliasing warnings, this can lead to unexpected behavior when building software and it would be great if it could be fixed.

It came up when updating RMG for the Gentoo repo. gentoo/gentoo#38837 (comment)

/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4IA_RGBA4444(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:55:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   55 |                 return IA88_RGBA4444(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B & 0x0F)) & 0x1FF]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:57:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   57 |                 return IA88_RGBA4444(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B >> 4)) & 0x1FF]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4IA_RGBA8888(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:65:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   65 |                 return IA88_RGBA8888(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B & 0x0F)) & 0x1FF]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:67:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   67 |                 return IA88_RGBA8888(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B >> 4)) & 0x1FF]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4RGBA_RGBA5551(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:75:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   75 |                 return RGBA5551_RGBA5551(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B & 0x0F)) & 0x1FF]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:77:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   77 |                 return RGBA5551_RGBA5551(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B >> 4)) & 0x1FF]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4RGBA_RGBA8888(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:85:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   85 |                 return RGBA5551_RGBA8888(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B & 0x0F)) & 0x1FF]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:87:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
   87 |                 return RGBA5551_RGBA8888(*(u16*)&TMEM[(0x100 + (palette << 4) + (color4B >> 4)) & 0x1FF]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8IA_RGBA4444(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:123:31: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  123 |         return IA88_RGBA4444(*(u16*)&TMEM[(0x100 + color) & 0x1FF]);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8IA_RGBA8888(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:129:31: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  129 |         return IA88_RGBA8888(*(u16*)&TMEM[(0x100 + color) & 0x1FF]);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8RGBA_RGBA5551(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:135:35: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  135 |         return RGBA5551_RGBA5551(*(u16*)&TMEM[(0x100 + color) & 0x1FF]);
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8RGBA_RGBA8888(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:141:35: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  141 |         return RGBA5551_RGBA8888(*(u16*)&TMEM[(0x100 + color) & 0x1FF]);
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI16IA_RGBA8888(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:196:27: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  196 |         const u16 col = (*(u16*)&TMEM[0x100 + (tex & 0xFF)]);
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI16IA_RGBA4444(u16, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:205:27: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  205 |         const u16 col = (*(u16*)&TMEM[0x100 + (tex & 0xFF)]);
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4IA_RGBA4444_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:306:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  306 |                 return IA88_RGBA4444(*(u16*)&TMEM[256 + (palette << 4) + (color4B & 0x0F)]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:308:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  308 |                 return IA88_RGBA4444(*(u16*)&TMEM[256 + (palette << 4) + (color4B >> 4)]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4IA_RGBA8888_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:316:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  316 |                 return IA88_RGBA8888(*(u16*)&TMEM[256 + (palette << 4) + (color4B & 0x0F)]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:318:39: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  318 |                 return IA88_RGBA8888(*(u16*)&TMEM[256 + (palette << 4) + (color4B >> 4)]);
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4RGBA_RGBA5551_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:326:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  326 |                 return RGBA5551_RGBA5551(*(u16*)&TMEM[256 + (palette << 4) + (color4B & 0x0F)]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:328:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  328 |                 return RGBA5551_RGBA5551(*(u16*)&TMEM[256 + (palette << 4) + (color4B >> 4)]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI4RGBA_RGBA8888_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:336:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  336 |                 return RGBA5551_RGBA8888(*(u16*)&TMEM[256 + (palette << 4) + (color4B & 0x0F)]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp:338:43: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  338 |                 return RGBA5551_RGBA8888(*(u16*)&TMEM[256 + (palette << 4) + (color4B >> 4)]);
      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8IA_RGBA4444_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:371:31: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  371 |         return IA88_RGBA4444(*(u16*)&TMEM[256 + ((u8*)src)[x ^ (i << 1)]]);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8IA_RGBA8888_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:376:31: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  376 |         return IA88_RGBA8888(*(u16*)&TMEM[256 + ((u8*)src)[x ^ (i << 1)]]);
      |                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8RGBA_RGBA5551_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:381:35: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  381 |         return RGBA5551_RGBA5551(*(u16*)&TMEM[256 + ((u8*)src)[x ^ (i << 1)]]);
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI8RGBA_RGBA8888_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:386:35: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  386 |         return RGBA5551_RGBA8888(*(u16*)&TMEM[256 + ((u8*)src)[x ^ (i << 1)]]);
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI16IA_RGBA8888_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:432:27: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  432 |         const u16 col = (*(u16*)&TMEM[256 + (tex & 0xFF)]);
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/GLideN64/src/Textures.cpp: In function ‘u32 GetCI16IA_RGBA4444_BG(u64*, u16, u16, u8)’:
/tmp/GLideN64/src/Textures.cpp:441:27: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
  441 |         const u16 col = (*(u16*)&TMEM[256 + (tex & 0xFF)]);
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[134/134] Linking CXX shared library plugin/Release/mupen64plus-video-GLideN64.so

[gonetz]

@orbea please check, if #2884 fixes the problem.

[orbea]

@gonetz I tested the PR and there are no more warnings, it also seems to work fine at runtime. Thanks!

[gonetz]

Ok, merged.