[Bug rtl-optimization/91137] [7/8/9/10 Regression] Wrong code with -O3

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91137

--- Comment #6 from bin cheng <amker at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #2)
> 
> and I can very well imagine we're getting confused by find_base_term
> logic here.
> 
> There's logic in IVOPTs to not generate IVs based on two different
> objects but somehow it doesn't trigger here.

Hmm, it's because determine_base_object failed to identify the `base_object`
for IV because it has non-pointer type:
IV struct:
  SSA_NAME:     _32
  Type: unsigned long
  Base: (unsigned long) &d + 19600
  Step: 4
  Biv:  N
  Overflowness wrto loop niter: Overflow

And we have short-circuit in determine_base_object:

static tree
determine_base_object (tree expr)
{
  enum tree_code code = TREE_CODE (expr);
  tree base, obj;

  /* If this is a pointer casted to any type, we need to determine
     the base object for the pointer; so handle conversions before
     throwing away non-pointer expressions.  */
  if (CONVERT_EXPR_P (expr))
    return determine_base_object (TREE_OPERAND (expr, 0));

  if (!POINTER_TYPE_P (TREE_TYPE (expr)))
    return NULL_TREE;

The IV is generated from inner loop ivopts as we rewrite using unsigned type.

Any suggestion how to fix this?