[Bug c/106439] New: RISC-V suboptimal codegen for large constants

[Bug c/106439] New: RISC-V suboptimal codegen for large constants

[vineet.gupta at linux dot dev]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106439

            Bug ID: 106439
           Summary: RISC-V suboptimal codegen for large constants
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vineet.gupta at linux dot dev
                CC: cmuellner at linux dot com, kito at gcc dot gnu.org,
                    wilson at gcc dot gnu.org
  Target Milestone: ---
            Target: riscv

As part of experiments to create smaller tests for 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106265, ran into a slightly
different issue involving large constants (> S12) and stack access.

RISC-V codegen for stack accesses with offsets > S12 is terrible. 

long foo(void)
{
        long a[512];
        return a[500];
}

output for rv64 -O2 : gcc trunk as of June 14 (commit 6abe341558ab)

foo:
        li      t0,-4096
        li      a5,4096
        add     sp,sp,t0
        addi    a5,a5,-96
        add     a5,a5,sp
        li      t0,4096
        ld      a0,0(a5)
        add     sp,sp,t0
        jr      ra

Compare the same code to aarch64:

foo:
        sub     sp, sp, #4096
        ldr     x0, [sp, 4000]
        add     sp, sp, 4096

Of course part of the problem is limited S12 offset encoding in RV LD, but the
compiler can definitely do much better.

[Bug target/106439] RISC-V suboptimal codegen for large constants

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106439

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is a dup of bug 105733.

*** This bug has been marked as a duplicate of bug 105733 ***