[gcc r13-5618] New reg note REG_CFA_NORESTORE

[Andreas Krebbel <krebbel@gcc.gnu.org>]

https://gcc.gnu.org/g:ef5f7b89bbc352255595069eb870d6f30f1f9134

commit r13-5618-gef5f7b89bbc352255595069eb870d6f30f1f9134
Author: Andreas Krebbel <krebbel@linux.ibm.com>
Date:   Wed Feb 1 08:59:41 2023 +0100

    New reg note REG_CFA_NORESTORE
    
    This patch introduces a new reg note which can be used to tell the CFI
    verification in dwarf2cfi that a register is stored without intending
    to restore from it.
    
    This is useful when storing e.g. register contents to the stack and
    generate CFI for it although the register is not really supposed to be
    restored.
    
    gcc/ChangeLog:
    
            * dwarf2cfi.cc (dwarf2out_frame_debug_cfa_restore): Add
            EMIT_CFI parameter.
            (dwarf2out_frame_debug): Add case for REG_CFA_NORESTORE.
            * reg-notes.def (REG_CFA_NOTE): New reg note definition.

Diff:
---
 gcc/dwarf2cfi.cc  | 15 ++++++++++-----
 gcc/reg-notes.def |  5 +++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/gcc/dwarf2cfi.cc b/gcc/dwarf2cfi.cc
index 1c70bd83f28..57283c10a29 100644
--- a/gcc/dwarf2cfi.cc
+++ b/gcc/dwarf2cfi.cc
@@ -1496,10 +1496,12 @@ dwarf2out_frame_debug_cfa_val_expression (rtx set)
   update_row_reg_save (cur_row, dwf_regno (dest), cfi);
 }
 
-/* A subroutine of dwarf2out_frame_debug, process a REG_CFA_RESTORE note.  */
+/* A subroutine of dwarf2out_frame_debug, process a REG_CFA_RESTORE
+   note. When called with EMIT_CFI set to false emitting a CFI
+   statement is suppressed.  */
 
 static void
-dwarf2out_frame_debug_cfa_restore (rtx reg)
+dwarf2out_frame_debug_cfa_restore (rtx reg, bool emit_cfi)
 {
   gcc_assert (REG_P (reg));
 
@@ -1507,7 +1509,8 @@ dwarf2out_frame_debug_cfa_restore (rtx reg)
   if (!span)
     {
       unsigned int regno = dwf_regno (reg);
-      add_cfi_restore (regno);
+      if (emit_cfi)
+	add_cfi_restore (regno);
       update_row_reg_save (cur_row, regno, NULL);
     }
   else
@@ -1522,7 +1525,8 @@ dwarf2out_frame_debug_cfa_restore (rtx reg)
 	  reg = XVECEXP (span, 0, par_index);
 	  gcc_assert (REG_P (reg));
 	  unsigned int regno = dwf_regno (reg);
-	  add_cfi_restore (regno);
+	  if (emit_cfi)
+	    add_cfi_restore (regno);
 	  update_row_reg_save (cur_row, regno, NULL);
 	}
     }
@@ -2309,6 +2313,7 @@ dwarf2out_frame_debug (rtx_insn *insn)
 	break;
 
       case REG_CFA_RESTORE:
+      case REG_CFA_NO_RESTORE:
 	n = XEXP (note, 0);
 	if (n == NULL)
 	  {
@@ -2317,7 +2322,7 @@ dwarf2out_frame_debug (rtx_insn *insn)
 	      n = XVECEXP (n, 0, 0);
 	    n = XEXP (n, 0);
 	  }
-	dwarf2out_frame_debug_cfa_restore (n);
+	dwarf2out_frame_debug_cfa_restore (n, REG_NOTE_KIND (note) == REG_CFA_RESTORE);
 	handled_one = true;
 	break;
 
diff --git a/gcc/reg-notes.def b/gcc/reg-notes.def
index 23de1f13ee9..1f74a605b3e 100644
--- a/gcc/reg-notes.def
+++ b/gcc/reg-notes.def
@@ -157,6 +157,11 @@ REG_CFA_NOTE (CFA_VAL_EXPRESSION)
    first pattern is the register to be restored.  */
 REG_CFA_NOTE (CFA_RESTORE)
 
+/* Like CFA_RESTORE but without actually emitting CFI.  This can be
+   used to tell the verification infrastructure that a register is
+   saved without intending to restore it.  */
+REG_CFA_NOTE (CFA_NO_RESTORE)
+
 /* Attached to insns that are RTX_FRAME_RELATED_P, marks insn that sets
    vDRAP from DRAP.  If vDRAP is a register, vdrap_reg is initalized
    to the argument, if it is a MEM, it is ignored.  */