[Bug tree-optimization/79191] potentially truncating unsigned conversion defeats range propagation

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79191

--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #2)
> When I add an explicit "-m64" to the compile command I get the same results
> as you, though. Also, it'd be nice if there were a warning from -Wconversion
> for the assignment from m to n in h. Or a warning from -Wimplicit-int for
> uses of bare "unsigned" without the "int" in general (I've actually been
> meaning to file a separate bug for that, but haven't gotten around to it
> yet).
> 

Actually looking back on the output there is actually a warning from
-Wconversion when I use -m64 so never mind about that part:

$ /usr/local/bin/gcc -c -O2 -S -Wall -fdump-tree-optimized=/dev/stdout -Wextra
-pedantic -Wconversion -m64 79191.c
79191.c: In function ‘h’:
79191.c:15:15: warning: conversion from ‘long unsigned int’ to ‘unsigned int’
may change value [-Wconversion]
  unsigned n = m;
               ^

;; Function f (f, funcdef_no=0, decl_uid=1832, cgraph_uid=0, symbol_order=0)

f (long unsigned int n)
{
  <bb 2> [100.00%] [count: INV]:
  if (n_1(D) > 3)
    goto <bb 3>; [0.04%] [count: 0]
  else
    goto <bb 4>; [99.96%] [count: INV]

  <bb 3> [0.04%] [count: 0]:
  __builtin_abort ();

  <bb 4> [99.96%] [count: INV]:
  return;

}



;; Function g (g, funcdef_no=1, decl_uid=1835, cgraph_uid=1, symbol_order=1)

g (unsigned int n)
{
  <bb 2> [100.00%] [count: INV]:
  return;

}



;; Function h (h, funcdef_no=2, decl_uid=1838, cgraph_uid=2, symbol_order=2)

Removing basic block 6
Removing basic block 7
h (long unsigned int m)
{
  unsigned int n;
  long unsigned int _5;

  <bb 2> [100.00%] [count: INV]:
  n_2 = (unsigned int) m_1(D);
  if (n_2 <= 2)
    goto <bb 3>; [50.00%] [count: INV]
  else
    goto <bb 5>; [50.00%] [count: INV]

  <bb 3> [50.00%] [count: INV]:
  _5 = m_1(D) & 4294967292;
  if (_5 != 0)
    goto <bb 4>; [0.04%] [count: 0]
  else
    goto <bb 5>; [99.96%] [count: INV]

  <bb 4> [0.02%] [count: 0]:
  __builtin_abort ();

  <bb 5> [99.98%] [count: INV]:
  return;

}


$