[Bug tree-optimization/107910] New: Missed optimization of struct members with mixed sizes

[Bug tree-optimization/107910] New: Missed optimization of struct members with mixed sizes

[pionere at freemail dot hu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107910

            Bug ID: 107910
           Summary: Missed optimization of struct members with mixed sizes
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pionere at freemail dot hu
  Target Milestone: ---

Store-merging generates suboptimal code to copy members of structs with
continuous memory:

#include <stdint.h>

#pragma pack(push, 1)
typedef struct StructA {
        int32_t v00;
        int32_t v01;
        int8_t v02_0;
        int8_t v02_1;
        int8_t v02_2;
        int8_t v02_3;
        int32_t v03;
        int32_t v04;
        int32_t v05;
        int32_t v06;
        int32_t v07;
        int32_t v08;
        int32_t v09;
        int32_t v10;
        int32_t v11;
} StructA;

typedef struct StructB {
        int32_t v00;
        int32_t v01;
        int32_t v02;
        int32_t v03;
        int32_t v04;
        int32_t v05;
        int32_t v06;
        int32_t v07;
        int32_t v08;
        int32_t v09;
        int32_t v10;
        int32_t v11;
} StructB;
#pragma pack(pop)

void copyA(StructA* __restrict dest, const StructA* __restrict src) {
        dest->v00 = src->v00;
        dest->v01 = src->v01;
        dest->v02_0 = src->v02_0;
        dest->v02_1 = src->v02_1;
        dest->v02_2 = src->v02_2;
        dest->v02_3 = src->v02_3;
        dest->v03 = src->v03;
}

void copyB(StructB* __restrict dest, const StructB* __restrict src) {
        dest->v00 = src->v00;
        dest->v01 = src->v01;
        dest->v02 = src->v02;
        dest->v03 = src->v03;
}

void copyAA(StructA* __restrict dest, const StructA* __restrict src) {
        dest->v00 = src->v00;
        dest->v01 = src->v01;
        dest->v02_0 = src->v02_0;
        dest->v02_1 = src->v02_1;
        dest->v02_2 = src->v02_2;
        dest->v02_3 = src->v02_3;
        dest->v03 = src->v03;
        dest->v04 = src->v04;
        dest->v05 = src->v05;
        dest->v06 = src->v06;
        dest->v07 = src->v07;
}

void copyBB(StructB* __restrict dest, const StructB* __restrict src) {
        dest->v00 = src->v00;
        dest->v01 = src->v01;
        dest->v02 = src->v02;
        dest->v03 = src->v03;
        dest->v04 = src->v04;
        dest->v05 = src->v05;
        dest->v06 = src->v06;
        dest->v07 = src->v07;
}

void copyAAA(StructA* __restrict dest, const StructA* __restrict src) {
        dest->v00 = src->v00;
        dest->v01 = src->v01;
        dest->v02_0 = src->v02_0;
        dest->v02_1 = src->v02_1;
        dest->v02_2 = src->v02_2;
        dest->v02_3 = src->v02_3;
        dest->v03 = src->v03;
        dest->v04 = src->v04;
        dest->v05 = src->v05;
        dest->v06 = src->v06;
        dest->v07 = src->v07;
        dest->v08 = src->v08;
        dest->v09 = src->v09;
        dest->v10 = src->v10;
        dest->v11 = src->v11;
}

void copyBBB(StructB* __restrict dest, const StructB* __restrict src) {
        dest->v00 = src->v00;
        dest->v01 = src->v01;
        dest->v02 = src->v02;
        dest->v03 = src->v03;
        dest->v04 = src->v04;
        dest->v05 = src->v05;
        dest->v06 = src->v06;
        dest->v07 = src->v07;
        dest->v08 = src->v08;
        dest->v09 = src->v09;
        dest->v10 = src->v10;
        dest->v11 = src->v11;
}

copyA* should generate the same code as its corresponding copyB* function.

Currently gcc 12 (or trunk) generates the following:

copyA(StructA*, StructA const*):
        mov     rax, QWORD PTR [rsi]
        mov     QWORD PTR [rdi], rax
        mov     rax, QWORD PTR [rsi+8]
        mov     QWORD PTR [rdi+8], rax
        ret
copyB(StructB*, StructB const*):
        movdqu  xmm0, XMMWORD PTR [rsi]
        movups  XMMWORD PTR [rdi], xmm0
        ret
copyAA(StructA*, StructA const*):
        mov     rax, QWORD PTR [rsi]
        movdqu  xmm0, XMMWORD PTR [rsi+12]
        mov     QWORD PTR [rdi], rax
        mov     eax, DWORD PTR [rsi+8]
        movups  XMMWORD PTR [rdi+12], xmm0
        mov     DWORD PTR [rdi+8], eax
        mov     eax, DWORD PTR [rsi+28]
        mov     DWORD PTR [rdi+28], eax
        ret
copyBB(StructB*, StructB const*):
        movdqu  xmm0, XMMWORD PTR [rsi+16]
        movdqu  xmm1, XMMWORD PTR [rsi]
        movups  XMMWORD PTR [rdi+16], xmm0
        movups  XMMWORD PTR [rdi], xmm1
        ret
copyAAA(StructA*, StructA const*):
        mov     rax, QWORD PTR [rsi]
        movdqu  xmm0, XMMWORD PTR [rsi+12]
        movdqu  xmm1, XMMWORD PTR [rsi+28]
        mov     QWORD PTR [rdi], rax
        mov     eax, DWORD PTR [rsi+8]
        movups  XMMWORD PTR [rdi+12], xmm0
        mov     DWORD PTR [rdi+8], eax
        mov     eax, DWORD PTR [rsi+44]
        movups  XMMWORD PTR [rdi+28], xmm1
        mov     DWORD PTR [rdi+44], eax
        ret
copyBBB(StructB*, StructB const*):
        movdqu  xmm1, XMMWORD PTR [rsi+16]
        movdqu  xmm0, XMMWORD PTR [rsi+32]
        movdqu  xmm2, XMMWORD PTR [rsi]
        movups  XMMWORD PTR [rdi+16], xmm1
        movups  XMMWORD PTR [rdi], xmm2
        movups  XMMWORD PTR [rdi+32], xmm0
        ret

[Bug tree-optimization/107910] Missed optimization of struct members with mixed sizes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107910

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The problem is an interaction between the SLP vectorizer and store merging.

[Bug tree-optimization/107910] Missed optimization of struct members with mixed sizes

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107910

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> The problem is an interaction between the SLP vectorizer and store merging.

Supposedly store-merging doesn't consider splitting loads/stores to re-merge
them.  Like with copying

struct StructC __attribute__((packed)) {
  int32_t v00;
  int32_t v01;
  int32_t v02;
  int64_t v03;
  int32_t v04;
};

[Bug tree-optimization/107910] Missed optimization of struct members with mixed sizes

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107910

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-11-30