Re: [PATCH] Adjust/remove REG_EQ{UAL,UIV} notes in REE (PR rtl-optimization/63659)

[Jeff Law <law at redhat dot com>]

On 10/27/14 14:47, Jakub Jelinek wrote:
> Hi!
>
> The following testcase is miscompiled in 4.8+ on x86_64 at -O2+,
> because REE widens for ZERO_EXTEND mode on
> (set (reg:QI ax) (const_int -1)) instruction to SImode, but doesn't
> adjust REG_EQUAL note of (const_int -1) also to (const_int 0xff)
> like it changes the pattern.
>
> The following patch attempts to adjust the notes if they are CONST_INT,
> or drop otherwise (not sure if it would be desirable to emit
> a ZERO_EXTEND of the previous content of the note), and both through
> validate_change, so that if we give up later on, it is undone.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> What about 4.9.2 (after release) and 4.8.x?
>
> 2014-10-27  Jakub Jelinek  <jakub@redhat.com>
>
> 	PR rtl-optimization/63659
> 	* ree.c (update_reg_equal_equiv_notes): New function.
> 	(combine_set_extension, transform_ifelse): Use it.
>
> 	* gcc.c-torture/execute/pr63659.c: New test.
Does this do the right thing in the case where there's multiple reaching 
definitions and one of those reaching definitions turns out to be 
non-combinable, while some other has a fixable REG_EQUAL note?

Don't we have to separate the check for a fixable note from the actual 
changing of the note?

Jeff