diff mbox series

combine: Fix PR84780 (more LOG_LINKS trouble)

Message ID f260ec22de585c97a6ab32b79f492f288c46e5f0.1520866892.git.segher@kernel.crashing.org
State New
Headers show
Series combine: Fix PR84780 (more LOG_LINKS trouble) | expand

Commit Message

Segher Boessenkool March 12, 2018, 3:21 p.m. UTC 
There still are situations where we have stale LOG_LINKS.  This causes
combine to try two-insn combinations I2->I3 where the register set by
I2 is used before I3 as well.  Not good.

This patch fixes it by checking for this situation in can_combine_p
(similar to what we already do for three and four insn combinations).

Longer term we should make sure stale LOG_LINKS are removed (or moved),
or ideally we should use DF instead of LOG_LINKS.

I tested the patch on 31 architectures, no degradations seen.  Zdenek
tested it on the original testcase (thanks!)

Committing to trunk.


Segher


2018-03-12  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/84169
	PR rtl-optimization/84780
	* combine.c (can_combine_p): Check for a 2-insn combination whether
	the destination register is used between the two insns, too.

---
 gcc/combine.c | 1 +
 1 file changed, 1 insertion(+)
diff mbox series

Patch

diff --git a/gcc/combine.c b/gcc/combine.c
index c9105ed..06a9ddd 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -1990,6 +1990,7 @@  can_combine_p (rtx_insn *insn, rtx_insn *i3, rtx_insn *pred ATTRIBUTE_UNUSED,
 	       && (reg_used_between_p (dest, succ2, i3)
 		   || reg_used_between_p (dest, succ, succ2)))
 	      || (!succ2 && succ && reg_used_between_p (dest, succ, i3))
+	      || (!succ2 && !succ && reg_used_between_p (dest, insn, i3))
 	      || (succ
 		  /* SUCC and SUCC2 can be split halves from a PARALLEL; in
 		     that case SUCC is not in the insn stream, so use SUCC2