[Bug target/78660] [7 Regression] 7.0 bootstrap fail on mips64el-unknow-linux: configure-stage2-target-libgcc' failed

["ebotcazou at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78660

--- Comment #15 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> So does LRA generate a full 64-bit load or an extended 32-to-64-bit load?

The former it seems, I can see:

(insn 218 211 8356 2 (set (reg:SI 4 $4 [2479])
        (ne:SI (reg:DI 22 $22 [orig:230 _3 ] [230])
            (const_int 0 [0]))) "/althome/mips/v6/src/gcc/gcc/c/c-decl.c":5551
505 {*sne_zero_disi}
     (nil))

(insn 8356 218 220 2 (set (mem/c:SI (plus:DI (reg/f:DI 29 $sp)
                (const_int 208 [0xd0])) [680 %sfp+208 S4 A64])
        (reg:SI 4 $4 [2479])) "/althome/mips/v6/src/gcc/gcc/c/c-decl.c":5551
312 {*movsi_internal}
     (nil))

[...]

(insn 8609 4185 4186 635 (set (reg/v:DI 2 $2 [orig:279 threadp ] [279])
        (mem/c:DI (plus:DI (reg/f:DI 29 $sp)
                (const_int 208 [0xd0])) [680 %sfp+208 S8 A64]))
"/althome/mips/v6/src/gcc/gcc/c/c-decl.c":6618 310 {*movdi_64bit}
     (nil))

That's incorrect, see what reload1.c:eliminate_regs_1 says about it:

          if (MEM_P (new_rtx)
              && ((x_size < new_size
                   /* On RISC machines, combine can create rtl of the form
                      (set (subreg:m1 (reg:m2 R) 0) ...)
                      where m1 < m2, and expects something interesting to
                      happen to the entire word.  Moreover, it will use the
                      (reg:m2 R) later, expecting all bits to be preserved.
                      So if the number of words is the same, preserve the
                      subreg so that push_reload can see it.  */
                   && !(WORD_REGISTER_OPERATIONS
                        && (x_size - 1) / UNITS_PER_WORD
                           == (new_size -1 ) / UNITS_PER_WORD))
                  || x_size == new_size)
              )
            return adjust_address_nv (new_rtx, GET_MODE (x), SUBREG_BYTE (x));
          else
            return gen_rtx_SUBREG (GET_MODE (x), new_rtx, SUBREG_BYTE (x));