[Bug rtl-optimization/96015] [10/11 Regression] gcc-10.1.0 miscompiles Python on hppa

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96015

--- Comment #27 from Sergei Trofimovich <slyfox at inbox dot ru> ---
If it's of any help by slightly expanding case switch I reproduced very similar
problem on both hppa and sh4 (but not on sparc or mips) with:

"""
int b, c;
int a() __attribute__((noipa));
int a(int *d, int *f, int g) {
  int e;
  if (d == f)
    e = 0;
  else
    e = 1;
  switch (g) {
  case 0:
    return e;
  case 1:
      return 7;
  case 2:
      return 8;
  case 3:
      return 8;
  case 4:
      return 1;
  case 5:
    if (e)
      return 10;
  default:
    __builtin_unreachable();
  }
}
int main() { return a(&b, &c, 0); }
"""

$ sh4-unknown-linux-gnu-gcc -fno-PIE -no-pie -fno-stack-protector
-U_FORTIFY_SOURCE -O2 bug_test.c -o bad-bug; ./bad-bug; echo $?
8

$ sh4-unknown-linux-gnu-gcc -fno-PIE -no-pie -fno-stack-protector
-U_FORTIFY_SOURCE -O2 -fno-delayed-branch bug_test.c -o good-bug; ./good-bug;
echo $?
1

bad-bug.S:

a:
        cmp/eq  r4,r5  ; if (d == f) // not our case
        bt/s    .L21   ;     goto .L21; something complicated on jump tables
         mov     #5,r1 ; +delay slot
.L6:
        .align 1
.L13:
        .align 1
.L14:
        rts            ; return 8
         mov     #8,r0 ; +delay slot
        .align 1
.L17:
        rts
         mov     #1,r0
        .align 1
.L21:
        mov     #4,r1
        cmp/hi  r1,r6
        bt/s    .L6
         mov     r6,r2
        mova    .L8,r0
        add     r2,r2
        mov.w   @(r0,r2),r1
        braf    r1
         nop
.L9:
        .align 2
.L8:
        .word   .L10-.L9
        .word   .L15-.L9
        .word   .L14-.L9
        .word   .L14-.L9
        .word   .L17-.L9
        .align 1
.L15:
        rts
        mov     #7,r0
        .align 1
.L10:
        rts
        mov     r6,r0

good-bug.S:

a:
        cmp/eq  r4,r5
        bt      .L21
         mov     #5,r1
        cmp/hi  r1,r6
        bf      .L22
.L6:
        .align 1
.L22:
        mova    .L12,r0
        mov.b   @(r0,r6),r6
        braf    r6
         nop
.L13:
        .align 2
.L12:
        .byte   .L17-.L13
        .byte   .L15-.L13
        .byte   .L14-.L13
        .byte   .L14-.L13
        .byte   .L17-.L13
        .byte   .L11-.L13
        .align 1
.L14:
        mov     #8,r0
        rts
         nop
        .align 1
.L17:
        mov     #1,r0
        rts
        nop
        .align 1
.L21:
        mov     #4,r1
        cmp/hi  r1,r6
        bt      .L6
         mova    .L8,r0
        mov     r6,r2
        add     r2,r2
        mov.w   @(r0,r2),r1
        braf    r1
         nop
.L9:
        .align 2
.L8:
        .word   .L10-.L9
        .word   .L15-.L9
        .word   .L14-.L9
        .word   .L14-.L9
        .word   .L17-.L9
        .align 1
.L15:
        mov     #7,r0
        rts
         nop
        .align 1
.L11:
        mov     #10,r0
        rts
         nop
        .align 1
.L10:
        mov     r6,r0
        rts
         nop

Might be not backend-specific? Or pa and sh have a similar bug.