[Bug target/79912] [7 regression] LRA unable to generate reloads after r245655

["npickito at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79912

--- Comment #4 from Kito Cheng <npickito at gmail dot com> ---
Hi Eric:
>> vfscanf.c: In function ‘_IO_vfscanf_internal’:
>> vfscanf.c:3050:1: error: unable to generate reloads for:
>> (insn 11026 11523 5651 1080 (set (reg:QI 3515)
>>         (mem/c:QI (plus:SI (reg/f:SI 65 frame)
>>                 (const_int -1568 [0xfffffffffffff9e0])) [65 %sfp+-1504 S1
>> A32])) "vfscanf.c":266 138 {*movqi_internal}
>>      (expr_list:REG_DEAD (reg:QI 3956)
>>         (nil)))

> I presume that it's not a valid address?  If so, why isn't it valid?

RISC-V have 12-bit signed immediate for offset (2047~-2048), so it's should be
valid address.




Here is another simple case in gcc testsuite:

riscv32-unknown-linux-gnu-gcc gcc/testsuite/gcc.c-torture/compile/pr52750.c -O0
-march=rv32imafd -mabi=ilp32d

/home/kito/riscv-workspace/riscv-gnu-toolchain/riscv-gcc/gcc/testsuite/gcc.c-torture/compile/pr52750.c:
In function ‘foo’:
/home/kito/riscv-workspace/riscv-gnu-toolchain/riscv-gcc/gcc/testsuite/gcc.c-torture/compile/pr52750.c:11:1:
error: unable to generate reloads for:
 }
 ^
(insn 194 197 145 2 (set (reg:QI 180)
        (mem/c:QI (plus:SI (reg/f:SI 65 frame)
                (const_int -268 [0xfffffffffffffef4])) [2 %sfp+-204 S1 A32]))
"/home/kito/riscv-workspace/riscv-gnu-toolchain/riscv-gcc/gcc/testsuite/gcc.c-torture/compile/pr52750.c":10
138 {*movqi_internal}
     (expr_list:REG_DEAD (reg:QI 183)
        (nil)))
/home/kito/riscv-workspace/riscv-gnu-toolchain/riscv-gcc/gcc/testsuite/gcc.c-torture/compile/pr52750.c:11:1:
internal compiler error: in curr_insn_transform, at lra-constraints.c:3785
0xa9f298 _fatal_insn(char const*, rtx_def const*, char const*, int, char
const*)
        ../../../src/gcc/trunk/gcc/rtl-error.c:108
0x9a2001 curr_insn_transform
        ../../../src/gcc/trunk/gcc/lra-constraints.c:3785
0x9a3286 lra_constraints(bool)
        ../../../src/gcc/trunk/gcc/lra-constraints.c:4754
0x98cf7c lra(_IO_FILE*)
        ../../../src/gcc/trunk/gcc/lra.c:2392
0x942ddb do_reload
        ../../../src/gcc/trunk/gcc/ira.c:5451
0x942ddb execute
        ../../../src/gcc/trunk/gcc/ira.c:5635
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