[PATCH] reload: Handle generating reloads that also clobbers flags

[Hans-Peter Nilsson <hp@axis.com>]

Regtested cris-elf with its LEGITIMIZE_RELOAD_ADDRESS
disabled, where it regresses gcc.target/cris/rld-legit1.c;
as expected, because that test guards proper function of its
LEGITIMIZE_RELOAD_ADDRESS i.e., that there's no sign of
decomposed address elements.

LRA also causes a similar decomposition (and worse, in even
smaller bits), but it can create valid insns as-is.
Unfortunately, it doesn't have something equivalent to
LEGITIMIZE_RELOAD_ADDRESS so it generates worse code for
cases where that hook helped reload.

I fear reload-related patches these days are treated like a
redheaded stepchild and even worse as this one is intended
for stage 1.  Either way, I need to create a reference to
it, and it's properly tested and has been a help when
working towards LRA, thus might help other targets: ok to
install for the next stage 1?

-- >8 --
When LEGITIMIZE_RELOAD_ADDRESS for cris-elf is disabled,
this code is now required for reload to generate valid insns
from some reload-decomposed addresses, for example the
(plus:SI
 (sign_extend:SI (mem:HI (reg/v/f:SI 32 [ a ]) [1 *a_6(D)+0 S2 A8]))
 (reg/v/f:SI 33 [ y ]))
generated in gcc.target/cris/rld-legit1.c (a valid address
but with two registers needing reload).  Now after decc0:ing,
most SET insns for former cc0 targets need to be a parallel
with a clobber of the flags register.  Such targets
typically have TARGET_FLAGS_REGNUM set to a valid register.

	* reload1.cc (emit_insn_if_valid_for_reload_1): Rename from
	emit_insn_if_valid_for_reload.
	(emit_insn_if_valid_for_reload): Call new helper, and if a SET fails
	to be recognized, also try emitting a parallel that clobbers
	TARGET_FLAGS_REGNUM, as applicable.
---
 gcc/reload1.cc | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/gcc/reload1.cc b/gcc/reload1.cc
index 7dcef50437b8..9ec2cb9baf4b 100644
--- a/gcc/reload1.cc
+++ b/gcc/reload1.cc
@@ -8377,11 +8377,11 @@ emit_reload_insns (class insn_chain *chain)
   reg_reloaded_dead |= reg_reloaded_died;
 }
 \f
-/* Go through the motions to emit INSN and test if it is strictly valid.
-   Return the emitted insn if valid, else return NULL.  */
+
+/* Helper for emit_insn_if_valid_for_reload.  */
 
 static rtx_insn *
-emit_insn_if_valid_for_reload (rtx pat)
+emit_insn_if_valid_for_reload_1 (rtx pat)
 {
   rtx_insn *last = get_last_insn ();
   int code;
@@ -8403,6 +8403,29 @@ emit_insn_if_valid_for_reload (rtx pat)
   return NULL;
 }
 
+/* Go through the motions to emit INSN and test if it is strictly valid.
+   Return the emitted insn if valid, else return NULL.  */
+
+static rtx_insn *
+emit_insn_if_valid_for_reload (rtx pat)
+{
+  rtx_insn *insn = emit_insn_if_valid_for_reload_1 (pat);
+
+  if (insn)
+    return insn;
+
+  /* If the pattern is a SET, and this target has a single
+     flags-register, try again with a PARALLEL that clobbers that
+     register.  */
+  if (targetm.flags_regnum == INVALID_REGNUM || GET_CODE (pat) != SET)
+    return NULL;
+
+  rtx flags_clobber = gen_hard_reg_clobber (CCmode, targetm.flags_regnum);
+  rtx parpat = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, pat, flags_clobber));
+
+  return emit_insn_if_valid_for_reload (parpat);
+}
+
 /* Emit code to perform a reload from IN (which may be a reload register) to
    OUT (which may also be a reload register).  IN or OUT is from operand
    OPNUM with reload type TYPE.
-- 
2.30.2