[Bug rtl-optimization/80301] Sub-optimal code with an array of structs offsetted inside a struct global on x86/x86_64 at -O2

[Bug rtl-optimization/80301] Sub-optimal code with an array of structs offsetted inside a struct global on x86/x86_64 at -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80301

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
We are able to do the 2->2 combine now (after r9-2064):
Trying 9 -> 10:
    9: {r87:DI=r86:DI+0x2;clobber flags:CC;}
      REG_DEAD r86:DI
      REG_UNUSED flags:CC
   10: flags:CCZ=cmp([r87:DI*0x8+`m'],r83:SI)
Failed to match this instruction:
(parallel [
        (set (reg:CCZ 17 flags)
            (compare:CCZ (mem:SI (plus:DI (mult:DI (reg:DI 86 [ indexD.2442 ])
                            (const_int 8 [0x8]))
                        (const:DI (plus:DI (symbol_ref:DI ("m") [flags 0x2] 
<var_decl 0x7fda6f169cf0 m>)
                                (const_int 16 [0x10])))) [1
mD.2375.sD.2374[index_4(D)].aD.2372+0 S4 A64])
                (reg:SI 83 [ <retval> ])))
        (set (reg:DI 87)
            (plus:DI (reg:DI 86 [ indexD.2442 ])
                (const_int 2 [0x2])))
    ])
Failed to match this instruction:
(parallel [
        (set (reg:CCZ 17 flags)
            (compare:CCZ (mem:SI (plus:DI (mult:DI (reg:DI 86 [ indexD.2442 ])
                            (const_int 8 [0x8]))
                        (const:DI (plus:DI (symbol_ref:DI ("m") [flags 0x2] 
<var_decl 0x7fda6f169cf0 m>)
                                (const_int 16 [0x10])))) [1
mD.2375.sD.2374[index_4(D)].aD.2372+0 S4 A64])
                (reg:SI 83 [ <retval> ])))
        (set (reg:DI 87)
            (plus:DI (reg:DI 86 [ indexD.2442 ])
                (const_int 2 [0x2])))
    ])
Successfully matched this instruction:
(set (reg:DI 87)
    (plus:DI (reg:DI 86 [ indexD.2442 ])
        (const_int 2 [0x2])))
Successfully matched this instruction:
(set (reg:CCZ 17 flags)
    (compare:CCZ (mem:SI (plus:DI (mult:DI (reg:DI 86 [ indexD.2442 ])
                    (const_int 8 [0x8]))
                (const:DI (plus:DI (symbol_ref:DI ("m") [flags 0x2]  <var_decl
0x7fda6f169cf0 m>)
                        (const_int 16 [0x10])))) [1
mD.2375.sD.2374[index_4(D)].aD.2372+0 S4 A64])
        (reg:SI 83 [ <retval> ])))
allowing combination of insns 9 and 10
original costs 4 + 13 = 17
replacement costs 4 + 13 = 17
modifying insn i2     9: r87:DI=r86:DI+0x2
deferring rescan insn with uid = 9.
modifying insn i3    10: flags:CCZ=cmp([r86:DI*0x8+const(`m'+0x10)],r83:SI)
      REG_DEAD r86:DI
deferring rescan insn with uid = 10.

But then we don't sink the add into the conditional and do the combine there.

The code we get now is:
func(unsigned int):
        movl    %edi, %edx
        movq    %rdx, %rax
        leaq    2(%rdx), %rcx
        cmpl    %edx, m+16(,%rdx,8)
        je      .L1
        movl    m+4(,%rcx,8), %eax
.L1:
        ret

[Bug rtl-optimization/80301] Sub-optimal code with an array of structs offsetted inside a struct global on x86/x86_64 at -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80301

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Starting in GCC 11, we try to prop the add into the mem but then fail with:
```
cannot propagate from insn 9 into insn 10: would create an invalid MEM
cannot propagate from insn 9 into insn 16: would create an invalid MEM
```

I wonder if the mem address gets simplified or not ...