[gcc/devel/ranger] dbr: Filter-out TARGET_FLAGS_REGNUM from end_of_function_needs.

[Aldy Hernandez]

https://gcc.gnu.org/g:2c2d405829ebb18de5357cc6319614035b420519

commit 2c2d405829ebb18de5357cc6319614035b420519
Author: Hans-Peter Nilsson <hp@axis.com>
Date:   Mon Feb 10 04:03:43 2020 +0100

    dbr: Filter-out TARGET_FLAGS_REGNUM from end_of_function_needs.
    
    Compared to the cc0 version, I noticed a regression in
    delay-slot-filling for CRIS for several functions in libgcc with
    a similar layout, one being lshrdi3, where with cc0 all
    delay-slots were filled, as exposed by the test-case in
    gcc.target/cris/pr93372-1.c.
    
    There's one slot that fails to be filled for the decc0rated CRIS
    port.  A gdb session shows it is because of the automatic
    inclusion of TARGET_FLAGS_REGNUM in "registers needed at the end
    of the function" because there are insns in the epilogue that
    clobber the condition-code register.  I'm not trying to tell a
    clobber from a set, as parallels with set instead of clobber
    seems likely to happen too, for targets with TARGET_FLAGS_REGNUM
    set.
    
    Other targets with delay-slots and one dedicated often-clobbered
    condition-code-register should consider defining
    TARGET_FLAGS_REGNUM.  I noticed it improved delay-slot-filling
    also in other situations than this.
    
    (Previously approved by Jeff Law.)
    
    gcc:
            * resource.c (init_resource_info): Filter-out TARGET_FLAGS_REGNUM
            from end_of_function_needs.

Diff:
---
 gcc/ChangeLog  | 5 +++++
 gcc/resource.c | 6 ++++++
 2 files changed, 11 insertions(+)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 75cc642b5a0..39330ba0515 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-09  Hans-Peter Nilsson  <hp@axis.com>
+
+	* resource.c (init_resource_info): Filter-out TARGET_FLAGS_REGNUM
+	from end_of_function_needs.
+
 2020-05-08  Vladimir Makarov  <vmakarov@redhat.com>
 
 	* ira-color.c (update_costs_from_allocno): Remove
diff --git a/gcc/resource.c b/gcc/resource.c
index 32faa73fd5f..0a9d5943abc 100644
--- a/gcc/resource.c
+++ b/gcc/resource.c
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "system.h"
 #include "coretypes.h"
 #include "backend.h"
+#include "target.h"
 #include "rtl.h"
 #include "df.h"
 #include "memmodel.h"
@@ -1215,6 +1216,11 @@ init_resource_info (rtx_insn *epilogue_insn)
 	break;
     }
 
+  /* Filter-out the flags register from those additionally required
+     registers. */
+  if (targetm.flags_regnum != INVALID_REGNUM)
+    CLEAR_HARD_REG_BIT (end_of_function_needs.regs, targetm.flags_regnum);
+
   /* Allocate and initialize the tables used by mark_target_live_regs.  */
   target_hash_table = XCNEWVEC (struct target_info *, TARGET_HASH_PRIME);
   bb_ticks = XCNEWVEC (int, last_basic_block_for_fn (cfun));