[PATCH][LRA]Don't generate reload for output scratch operand from reload instruction.

[Renlin Li <renlin dot li at foss dot arm dot com>]

Hi all,

I admit that, the title looks a little bit confusing.

The situation is like this,
To make insn_1 strict, lra generates a new insn_1_reload insn.
In insn_1_reload, there is a scratch operand with this form
clobber (match_scratch:MODE x "=&r")

When lra tries to reload insn_1_reload in later iteration, a new pseudo
register (let say RXX) is created to replace this scratch operand in-place.
Additionally, a new insn will be generated and inserted after insn_1_reload to
finish the reload. It's in this form:
(set scratch, RXX)

And this instruction is illegal. no target implements this kind of pattern.
LRA will ICE because of this.
"internal compiler error: in lra_set_insn_recog_data, at lra.c:964"

And indeed, this pattern has no side-effect. The scratch operand should
stay inside the pattern.

Normally, at the very beginning of LRA reload, all scratch operands will be
replaced by newly created pseudo register. However, this is a problem when
generated reload insn has output scratch operand.

I have checked, x86, arm, aarch64, mips, arc all have such patterns. But it's
not triggered. In my case, it's triggered by compiling glibc with local change.

So a simple change is made in this patch. The output operand is reloaded only
when it's not a scratch operand and it's not unused since then.


aarch64-none-linux-gnu bootstrap and regression test OK.
x86_64-linux bootstrap and regression test OK.
OK for trunk?

Regards,
Renlin Li


gcc/ChangeLog:

2016-02-26  Renlin Li<renlin.li@arm.com>

	* lra-constraints.c (curr_insn_transform): Don't generate reload for
	output scratch operand.

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index 08cf0aa6c4208bb60ba5071bad1255d587f1cb4a..ef5809ff226cca69bb711bfc5dab55e24caba01a 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -3882,6 +3882,8 @@ curr_insn_transform (bool check_only_p)
 	    }
 	  *loc = new_reg;
 	  if (type != OP_IN
+	      /* Don't generate reload for output scratch operand.  */
+	      && GET_CODE (old) != SCRATCH
 	      && find_reg_note (curr_insn, REG_UNUSED, old) == NULL_RTX)
 	    {
 	      start_sequence ();