Bug in alias analysis

[Unruh, Erwin]

Hello,

I have found an error in the alias analysis. It occurs when ptr_mode and Pmode
have different sizes. The scenario:

- a symbol_ref is constructed, with Pmode == DImode (symbol_ref:DI)
- The rtl is converted to ptr_mode == SImode
- function convert_memory_address now constructs a symbol_ref:SI

while optimizing (cse pass) cse_insn indirectly calls true_dependance.
- this calls base_alias_check
- this extracts (via find_base_term) the symbol_ref parts.
- one of them got through the conversion above and is symbol_ref:SI
  the other is unchanged and is a symbol_ref:DI

Now rtx_equal_p is called and it doesn't recognize the similarity because of the
mode difference.

Now my question: what is the best way to handle the problem?

- Avoid the generation of a symbol_ref:SI
- handle mode problems in find_base_term
- add another check in base_alias_check
- modify rtx_equal_p to allow mode differences in symbol_ref

Do you have an advice?

        Erwin

Erwin Unruh, Fujitsu Siemens Computers, C/C++ compiler group