Re: Indirect memory addresses vs. lra

[Vladimir Makarov <vmakarov@redhat.com>]

On 8/15/19 1:35 PM, John Darrington wrote:
> On Thu, Aug 15, 2019 at 12:29:13PM -0400, Vladimir Makarov wrote:
>
>
>       Thank you for providing the sources.?? It helped me to understand what is
>       going on.?? So the test crashes on
>       
>       /home/jmd/Source/GCC2/gcc/testsuite/gcc.c-torture/compile/pr53410-2.c: In function ???f1???:
>       /home/jmd/Source/GCC2/gcc/testsuite/gcc.c-torture/compile/pr53410-2.c:10:1: error: unable to find a register to spill
>       /home/jmd/Source/GCC2/gcc/testsuite/gcc.c-torture/compile/pr53410-2.c:10:1: error: this is the insn:
>       (insn 14 49 15 2 (set (mem:SI (plus:PSI (reg/f:PSI 40 [34])
>                       (const_int 32 [0x20])) [2  S4 A64])
>               (mem:SI (reg:PSI 41) [2 *p_5(D)+0 S4 A8])) "/home/jmd/Source/GCC2/gcc/testsuite/gcc.c-torture/compile/pr53410-2.c":9:9 95 {*movsi}
>            (expr_list:REG_DEAD (reg:PSI 41)
>               (expr_list:REG_DEAD (reg/f:PSI 40 [34])
>                   (nil))))
>
> Thanks for taking a look.
>       
>       Your target has only 2 non-fixed addr registers (r8, r9).  One (r9) is defined as a hard reg pointer pointer.
>
> That is correct.
>
>       Honestly, I never saw a target with such register constraints.
>
> My recollection is that MC68HC11 was the same.
>       
>       So what can be done, imho.  The simplest solution would be preventing insns with more one memory operand.
>
> I tried this solution earlier.  But unfortunately it makes things worse.  What happens is it libgcc cannot
> even be built -- ICEs occur on a memory from  address reg insn such as:
>       
> (insn 117 2981 3697 5 (set (mem/f:PSI (plus:PSI (reg:PSI 1309)
>                  (const_int 102 [0x66])) [3 fs_129(D)->pc+0 S4 A8])
> 		        (reg:PSI 1310)) "/home/jmd/Source/GCC2/libgcc/unwind-dw2.c":977:9 96 {movpsi}
>
I see.  Then for the insn, you could try to create a pattern 
"memory,special memory constraint".  The special memory constraint 
should satisfy only spilled pseudo (pseudo with reg_renumber == -1).  I 
believe lra-constraints.c can spill the pseudo and the end you will have 
mem[disp1 + r8|r9|sp] = mem[disp1+sp].

It might work.  If it is not, we could modify LRA to do this.

Another solution would be adding unexisting register Z and for mem:psi 
[psi:r] = Z you could emit an assembler insn : mem[psi:r] = a stack slot 
corresponding Z.