[Bug middle-end/126153] [13/14/15/16/17 Regression] [csmith] runtime crash with -O3 -ftrivial-auto-var-init=zero

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126153

--- Comment #17 from Richard Biener <rguenth at gcc dot gnu.org> ---
So it seems to be IPA CP transform going wrong, we do

replacing stmt:g_8[g_10.32_1149] = func_22 (_1148, _1130, 35, _1128, l_59); 
with stmt:g_8[g_10.32_1149] = func_22.constprop (l_59);
...
t2.c:3933:70: note: Inlining func_22.constprop/556 to main/177 with frequency
363.71

we then have

   MEM <char> [(struct S1 *)&l_59 + 13B] = 4;
...
   p_27 = l_59;
...
  _1172 = p_27.f3.f7;

which SRA decomposes:

Created a replacement for p_27 offset: 40, size: 15: p_27$f3$f0D.9115
Created a replacement for p_27 offset: 73, size: 14: p_27$5$f3D.9116
Created a replacement for p_27 offset: 106, size: 3: p_27$f3$f7D.9117

  p_27 = l_59;
  p_27$f3$f0_412 = MEM <struct S0> [(struct S1 *)&l_59 + 5B].f0;
  p_27$5$f3_405 = MEM <struct S0> [(struct S1 *)&l_59 + 5B].f3;
  p_27$f3$f7_484 = MEM <struct S0> [(struct S1 *)&l_59 + 5B].f7;
...
  _1172 = p_27$f3$f7_484;

which is where a mismatch must occur (probably with respect to the packedness).

PRE sees

  MEM <char> [(struct S1 *)&l_59 + 13B] = 4;
  g_11 = 3;
  p_27$f3$f7_484 = MEM <struct S0> [(struct S1 *)&l_59 + 5B].f7;

and

Value numbering stmt = p_27$f3$f7_484 = MEM <struct S0> [(struct S1 *)&l_59 +
5B].f7;
Setting value number of p_27$f3$f7_484 to 1 (changed)

disabling late SRA resolves the segfault (we no longer fall through main),
but we still get the checksum mis-calculated.

The testcase is quite hard to analyze directly (and offsets to be verified),
but there seems to be errors in multiple places.  SRA possibly mis-handles
the aggregate copy between p_27 and l_59 and IPA-CP possibly has errors
on its own (maybe does not handle bit-fields very well?).