combine.cc (make_more_copies): Copy attributes from the original pseudo, PR115883

The first of the late-combine passes, propagates some of the copies
made during the (in-time-)combine pass in make_more_copies into the
users of the "original" pseudo registers and removes the "old"
pseudos.  That effectively removes attributes such as REG_POINTER,
which matter to LRA.  The quoted PR is for an ICE-manifesting bug that
was exposed by the late-combine pass and went back to hiding with this
patch until commit r15-2937-g3673b7054ec2, the fix for PR116236, when
it was actually fixed.  To wit, this patch is only incidentally
related to that bug.

In other words, the REG_POINTER attribute should not be required for
LRA to work correctly.  This patch merely corrects state for those
propagated register-uses to ante late-combine.

For reasons not investigated, this fixes a failing test
"FAIL: gcc.dg/guality/pr54200.c -Og -DPREVENT_OPTIMIZATION line 20 z == 3"
for x86_64-linux-gnu.

	PR middle-end/115883
	* combine.cc (make_more_copies): Copy attributes from the original
	pseudo to the new copy.

1 files changed, 6 insertions, 0 deletions

diff --git a/gcc/combine.cc b/gcc/combine.cc
index 40e9294..fef06a6 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -15102,6 +15102,12 @@ make_more_copies (void)
 	    continue;
 
 	  rtx new_reg = gen_reg_rtx (GET_MODE (dest));
+
+	  /* The "original" pseudo copies have important attributes
+	     attached, like pointerness.  We want that for these copies
+	     too, for use by insn recognition and later passes.  */
+	  set_reg_attrs_from_value (new_reg, dest);
+
 	  rtx_insn *new_insn = gen_move_insn (new_reg, src);
 	  SET_SRC (set) = new_reg;
 	  emit_insn_before (new_insn, insn);