combine: Don't create REG_UNUSED notes if the reg already died (PR99927)

If the register named in an existing REG_UNUSED note dies somewhere
between where the note used to be and I3, we should just drop it.

2021-04-21  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/99927
	* combine.c (distribute_notes) [REG_UNUSED]: If the register already
	is dead, just drop it.

diff --git a/gcc/combine.c b/gcc/combine.c
index 9063a07..62bf4ae 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -14366,6 +14366,11 @@ distribute_notes (rtx notes, rtx_insn *from_insn, rtx_insn *i3, rtx_insn *i2,
             we keep notes from i2 or i1 if they will turn into REG_DEAD
             notes.  */
 
+         /* If this register is set or clobbered between FROM_INSN and I3,
+            we should not create a note for it.  */
+         if (reg_set_between_p (XEXP (note, 0), from_insn, i3))
+           break;
+
          /* If this register is set or clobbered in I3, put the note there
             unless there is one already.  */
          if (reg_set_p (XEXP (note, 0), PATTERN (i3)))