[M3devel] code quality..

Tony Hosking hosking at cs.purdue.edu
Mon Jan 21 17:01:52 CET 2008


Is this having the front-end handle return of structs or the backend?

On Jan 21, 2008, at 9:50 AM, Jay wrote:

> Unoptimized code quality is really bad,
>  even compared to unoptimized C, even compared
>  to gcc, and optimized code quality isn't great.
>
> I have this made up C code. I was verifying
> the struct return calling convention.
>
> typedef struct {
>   unsigned a;
>   unsigned b;
>   unsigned c;
> } d;
>
> d F2(unsigned a, unsigned b, unsigned c)
> {
>   d e;
>   e.a = a * b * c;
>   e.b = 123;
>   e.c = a - b - c;
>   return e;
> }
>
> and then the equivalent Modula-3:
>
> INTERFACE T;
>
> TYPE T1 = RECORD
>   a,b,c : INTEGER
> END;
>
> PROCEDURE F2(a,b,c : INTEGER) : T1;
>
> END T.
>
> MODULE T;
>
> PROCEDURE F2(a,b,c : INTEGER) : T1 =
> VAR
>  e : T1;
> BEGIN
>   e.a := (a * b * c);
>   e.b := 123;
>   e.c := (a - b - c);
>   RETURN e;
> END F2;
>
> BEGIN
> END T.
>
> Unoptimized Visual C++ 8.0:
>
> _F2:
>   00000000: 55                 push        ebp
>   00000001: 8B EC              mov         ebp,esp
>   00000003: 83 EC 0C           sub         esp,0Ch
>   00000006: 8B 45 0C           mov         eax,dword ptr [ebp+0Ch]
>   00000009: 0F AF 45 10        imul        eax,dword ptr [ebp+10h]
>   0000000D: 0F AF 45 14        imul        eax,dword ptr [ebp+14h]
>   00000011: 89 45 F4           mov         dword ptr [ebp-0Ch],eax
>   00000014: C7 45 F8 7B 00 00  mov         dword ptr [ebp-8],7Bh
>             00
>   0000001B: 8B 4D 0C           mov         ecx,dword ptr [ebp+0Ch]
>   0000001E: 2B 4D 10           sub         ecx,dword ptr [ebp+10h]
>   00000021: 2B 4D 14           sub         ecx,dword ptr [ebp+14h]
>   00000024: 89 4D FC           mov         dword ptr [ebp-4],ecx
>   00000027: 8B 55 08           mov         edx,dword ptr [ebp+8]
>   0000002A: 8B 45 F4           mov         eax,dword ptr [ebp-0Ch]
>   0000002D: 89 02              mov         dword ptr [edx],eax
>   0000002F: 8B 4D F8           mov         ecx,dword ptr [ebp-8]
>   00000032: 89 4A 04           mov         dword ptr [edx+4],ecx
>   00000035: 8B 45 FC           mov         eax,dword ptr [ebp-4]
>   00000038: 89 42 08           mov         dword ptr [edx+8],eax
>   0000003B: 8B 45 08           mov         eax,dword ptr [ebp+8]
>   0000003E: 8B E5              mov         esp,ebp
>   00000040: 5D                 pop         ebp
>   00000041: C3                 ret
>
> Visual C++ 8.0 with /O1
>
> It writes the results right into the output.
> _F2:
>   00000000: 55                 push        ebp
>   00000001: 8B EC              mov         ebp,esp
>   00000003: 8B 4D 0C           mov         ecx,dword ptr [ebp+0Ch]
>   00000006: 8B 45 08           mov         eax,dword ptr [ebp+8]
>   00000009: 8B D1              mov         edx,ecx
>   0000000B: 0F AF 55 10        imul        edx,dword ptr [ebp+10h]
>   0000000F: 0F AF 55 14        imul        edx,dword ptr [ebp+14h]
>   00000013: 2B 4D 10           sub         ecx,dword ptr [ebp+10h]
>   00000016: 89 10              mov         dword ptr [eax],edx
>   00000018: 2B 4D 14           sub         ecx,dword ptr [ebp+14h]
>   0000001B: C7 40 04 7B 00 00  mov         dword ptr [eax+4],7Bh
>             00
>   00000022: 89 48 08           mov         dword ptr [eax+8],ecx
>   00000025: 5D                 pop         ebp
>   00000026: C3                 ret
>
> with /O2
>
> _F2:
>   00000000: 8B 4C 24 08        mov         ecx,dword ptr [esp+8]
>   00000004: 8B 54 24 0C        mov         edx,dword ptr [esp+0Ch]
>   00000008: 8B 44 24 04        mov         eax,dword ptr [esp+4]
>   0000000C: 56                 push        esi
>   0000000D: 8B 74 24 14        mov         esi,dword ptr [esp+14h]
>   00000011: 57                 push        edi
>   00000012: 8B F9              mov         edi,ecx
>   00000014: 0F AF FA           imul        edi,edx
>   00000017: 0F AF FE           imul        edi,esi
>   0000001A: 2B CA              sub         ecx,edx
>   0000001C: 89 38              mov         dword ptr [eax],edi
>   0000001E: 2B CE              sub         ecx,esi
>   00000020: 5F                 pop         edi
>   00000021: C7 40 04 7B 00 00  mov         dword ptr [eax+4],7Bh
>             00
>   00000028: 89 48 08           mov         dword ptr [eax+8],ecx
>   0000002B: 5E                 pop         esi
>   0000002C: C3                 ret
>
> gcc 3.4.5 unoptimized
>
> _F2:
>   00000000: 55                 push        ebp
>   00000001: 89 E5              mov         ebp,esp
>   00000003: 83 EC 18           sub         esp,18h
>   00000006: 8B 4D 08           mov         ecx,dword ptr [ebp+8]
>   00000009: 8B 45 0C           mov         eax,dword ptr [ebp+0Ch]
>   0000000C: 0F AF 45 10        imul        eax,dword ptr [ebp+10h]
>   00000010: 0F AF 45 14        imul        eax,dword ptr [ebp+14h]
>   00000014: 89 45 E8           mov         dword ptr [ebp-18h],eax
>   00000017: C7 45 EC 7B 00 00  mov         dword ptr [ebp-14h],7Bh
>             00
>   0000001E: 8B 55 10           mov         edx,dword ptr [ebp+10h]
>   00000021: 8B 45 0C           mov         eax,dword ptr [ebp+0Ch]
>   00000024: 29 D0              sub         eax,edx
>   00000026: 2B 45 14           sub         eax,dword ptr [ebp+14h]
>   00000029: 89 45 F0           mov         dword ptr [ebp-10h],eax
>   0000002C: 8B 45 E8           mov         eax,dword ptr [ebp-18h]
>   0000002F: 89 01              mov         dword ptr [ecx],eax
>   00000031: 8B 45 EC           mov         eax,dword ptr [ebp-14h]
>   00000034: 89 41 04           mov         dword ptr [ecx+4],eax
>   00000037: 8B 45 F0           mov         eax,dword ptr [ebp-10h]
>   0000003A: 89 41 08           mov         dword ptr [ecx+8],eax
>   0000003D: 89 C8              mov         eax,ecx
>   0000003F: C9                 leave
>   00000040: C2 04 00           ret         4
>   00000043: 90                 nop
>   00000044: 90                 nop
>  ...more nops for padding...
>
> gcc -O1
>
> _F2:
>   00000000: 55                 push        ebp
>   00000001: 89 E5              mov         ebp,esp
>   00000003: 83 EC 18           sub         esp,18h
>   00000006: 89 5D F8           mov         dword ptr [ebp-8],ebx
>   00000009: 89 75 FC           mov         dword ptr [ebp-4],esi
>   0000000C: 8B 45 08           mov         eax,dword ptr [ebp+8]
>   0000000F: 8B 4D 0C           mov         ecx,dword ptr [ebp+0Ch]
>   00000012: 8B 5D 10           mov         ebx,dword ptr [ebp+10h]
>   00000015: 8B 75 14           mov         esi,dword ptr [ebp+14h]
>   00000018: 89 CA              mov         edx,ecx
>   0000001A: 0F AF D3           imul        edx,ebx
>   0000001D: 0F AF D6           imul        edx,esi
>   00000020: 29 D9              sub         ecx,ebx
>   00000022: 29 F1              sub         ecx,esi
>   00000024: 89 10              mov         dword ptr [eax],edx
>   00000026: C7 40 04 7B 00 00  mov         dword ptr [eax+4],7Bh
>             00
>   0000002D: 89 48 08           mov         dword ptr [eax+8],ecx
>   00000030: 8B 5D F8           mov         ebx,dword ptr [ebp-8]
>   00000033: 8B 75 FC           mov         esi,dword ptr [ebp-4]
>   00000036: 89 EC              mov         esp,ebp
>   00000038: 5D                 pop         ebp
>   00000039: C2 04 00           ret         4
>   0000003C: 90                 nop
>   0000003D: 90                 nop
>   0000003E: 90                 nop
>   0000003F: 90                 nop
>
> I didn't investigate all the switches much and simple -O vs. -O1  
> vs. -O2 vs. -o3
> all do the same.
>
> -O1 -fomit-frame-pointer netted:
>
> _F2:
>   00000000: 83 EC 1C           sub         esp,1Ch
>   00000003: 89 5C 24 14        mov         dword ptr [esp+14h],ebx
>   00000007: 89 74 24 18        mov         dword ptr [esp+18h],esi
>   0000000B: 8B 44 24 20        mov         eax,dword ptr [esp+20h]
>   0000000F: 8B 4C 24 24        mov         ecx,dword ptr [esp+24h]
>   00000013: 8B 5C 24 28        mov         ebx,dword ptr [esp+28h]
>   00000017: 8B 74 24 2C        mov         esi,dword ptr [esp+2Ch]
>   0000001B: 89 CA              mov         edx,ecx
>   0000001D: 0F AF D3           imul        edx,ebx
>   00000020: 0F AF D6           imul        edx,esi
>   00000023: 29 D9              sub         ecx,ebx
>   00000025: 29 F1              sub         ecx,esi
>   00000027: 89 10              mov         dword ptr [eax],edx
>   00000029: C7 40 04 7B 00 00  mov         dword ptr [eax+4],7Bh
>             00
>   00000030: 89 48 08           mov         dword ptr [eax+8],ecx
>   00000033: 8B 5C 24 14        mov         ebx,dword ptr [esp+14h]
>   00000037: 8B 74 24 18        mov         esi,dword ptr [esp+18h]
>   0000003B: 83 C4 1C           add         esp,1Ch
>   0000003E: C2 04 00           ret         4
>   00000041: 90                 nop
>   .. more nops ..
>
> Ok, ready, here goes the unoptimized Modula-3.
> Notice the duplicate copying of the return value and the *doubling*  
> in code size.
>
> _T__F2:
>   00000000: 55                 push        ebp
>   00000001: 89 E5              mov         ebp,esp
>   00000003: 57                 push        edi
>   00000004: 56                 push        esi
>   00000005: 83 EC 30           sub         esp,30h
>   00000008: 8B 55 0C           mov         edx,dword ptr [ebp+0Ch]
>   0000000B: 8B 45 10           mov         eax,dword ptr [ebp+10h]
>   0000000E: 0F AF D0           imul        edx,eax
>   00000011: 8B 45 14           mov         eax,dword ptr [ebp+14h]
>   00000014: 0F AF D0           imul        edx,eax
>   00000017: 8B 45 D4           mov         eax,dword ptr [ebp-2Ch]
>   0000001A: 83 E0 00           and         eax,0
>   0000001D: 09 D0              or          eax,edx
>   0000001F: 89 45 D4           mov         dword ptr [ebp-2Ch],eax
>   00000022: 8B 45 D8           mov         eax,dword ptr [ebp-28h]
>   00000025: 83 E0 00           and         eax,0
>   00000028: 83 C8 7B           or          eax,7Bh
>   0000002B: 89 45 D8           mov         dword ptr [ebp-28h],eax
>   0000002E: 8B 55 0C           mov         edx,dword ptr [ebp+0Ch]
>   00000031: 8B 45 10           mov         eax,dword ptr [ebp+10h]
>   00000034: 29 C2              sub         edx,eax
>   00000036: 8B 45 14           mov         eax,dword ptr [ebp+14h]
>   00000039: 29 C2              sub         edx,eax
>   0000003B: 8B 45 DC           mov         eax,dword ptr [ebp-24h]
>   0000003E: 83 E0 00           and         eax,0
>   00000041: 09 D0              or          eax,edx
>   00000043: 89 45 DC           mov         dword ptr [ebp-24h],eax
>   00000046: 8B 45 08           mov         eax,dword ptr [ebp+8]
>   00000049: 89 C2              mov         edx,eax
>   0000004B: 8D 45 D4           lea         eax,[ebp-2Ch]
>   0000004E: 8D 7D EC           lea         edi,[ebp-14h]
>   00000051: 89 C6              mov         esi,eax
>   00000053: FC                 cld
>   00000054: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   00000055: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   00000056: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   00000057: 89 D7              mov         edi,edx
>   00000059: 8D 75 EC           lea         esi,[ebp-14h]
>   0000005C: FC                 cld
>   0000005D: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   0000005E: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   0000005F: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   00000060: 83 C4 30           add         esp,30h
>   00000063: 5E                 pop         esi
>   00000064: 5F                 pop         edi
>   00000065: C9                 leave
>   00000066: C3                 ret
>
>  optimized Modula-3 is better, saves the extra copy, but still not  
> great:
>
> _T__F2:
>   00000000: 55                 push        ebp
>   00000001: 89 E5              mov         ebp,esp
>   00000003: 57                 push        edi
>   00000004: 56                 push        esi
>   00000005: 53                 push        ebx
>   00000006: 83 EC 10           sub         esp,10h
>   00000009: 8B 55 0C           mov         edx,dword ptr [ebp+0Ch]
>   0000000C: 8B 4D 10           mov         ecx,dword ptr [ebp+10h]
>   0000000F: 8B 5D 14           mov         ebx,dword ptr [ebp+14h]
>   00000012: 89 D0              mov         eax,edx
>   00000014: 0F AF C1           imul        eax,ecx
>   00000017: 0F AF C3           imul        eax,ebx
>   0000001A: 8B 75 E8           mov         esi,dword ptr [ebp-18h]
>   0000001D: 89 45 E8           mov         dword ptr [ebp-18h],eax
>   00000020: 8B 45 EC           mov         eax,dword ptr [ebp-14h]
>   00000023: C7 45 EC 7B 00 00  mov         dword ptr [ebp-14h],7Bh
>             00
>   0000002A: 29 CA              sub         edx,ecx
>   0000002C: 29 DA              sub         edx,ebx
>
>  Huh what does this next instruction achieve?
>   0000002E: 8B 45 F0           mov         eax,dword ptr [ebp-10h]
>   00000031: 89 55 F0           mov         dword ptr [ebp-10h],edx
>   00000034: 8B 7D 08           mov         edi,dword ptr [ebp+8]
>   00000037: 8D 75 E8           lea         esi,[ebp-18h]
>   0000003A: FC                 cld
>   0000003B: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   0000003C: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   0000003D: A5                 movs        dword ptr es:[edi],dword  
> ptr [esi]
>   0000003E: 83 C4 10           add         esp,10h
>   00000041: 5B                 pop         ebx
>   00000042: 5E                 pop         esi
>   00000043: 5F                 pop         edi
>   00000044: C9                 leave
>   00000045: C3                 ret
>
> and lastly the integrated backend, which runs much faster, and I  
> believe has just one mode,
> somewhat optimized (but still lacks int64 support):
>
> _T__F2:
>   00000000: 55                 push        ebp
>   00000001: 8B EC              mov         ebp,esp
>   00000003: 81 EC 18 00 00 00  sub         esp,18h
>   00000009: 53                 push        ebx
>   0000000A: 56                 push        esi
>   0000000B: 57                 push        edi
>   0000000C: 8B 5D 10           mov         ebx,dword ptr [ebp+10h]
>   0000000F: 0F AF 5D 0C        imul        ebx,dword ptr [ebp+0Ch]
>   00000013: 0F AF 5D 14        imul        ebx,dword ptr [ebp+14h]
>   00000017: 89 5D F4           mov         dword ptr [ebp-0Ch],ebx
>   0000001A: C7 45 F8 7B 00 00  mov         dword ptr [ebp-8],7Bh
>             00
>   00000021: 8B 55 0C           mov         edx,dword ptr [ebp+0Ch]
>   00000024: 2B 55 10           sub         edx,dword ptr [ebp+10h]
>   00000027: 2B 55 14           sub         edx,dword ptr [ebp+14h]
>   0000002A: 89 55 FC           mov         dword ptr [ebp-4],edx
>   0000002D: 8D 75 F4           lea         esi,[ebp-0Ch]
>   00000030: 8B 7D 08           mov         edi,dword ptr [ebp+8]
>   00000033: 8B 4E 00           mov         ecx,dword ptr [esi]
>   00000036: 89 4F 00           mov         dword ptr [edi],ecx
>   00000039: 8B 4E 04           mov         ecx,dword ptr [esi+4]
>   0000003C: 89 4F 04           mov         dword ptr [edi+4],ecx
>   0000003F: 8B 4E 08           mov         ecx,dword ptr [esi+8]
>   00000042: 89 4F 08           mov         dword ptr [edi+8],ecx
>   00000045: 8B C7              mov         eax,edi
>   00000047: 5F                 pop         edi
>   00000048: 5E                 pop         esi
>   00000049: 5B                 pop         ebx
>   0000004A: C9                 leave
>   0000004B: C3                 ret
>
>  I haven't looked at all this in depth, but the doubling in size,  
> the extra copy,
>   that the integrated backend's code is fairly small...
>
>  - Jay
>
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