[PATCH 1/2] New reg note REG_CFA_NORESTORE

[Andreas Krebbel <krebbel@linux.ibm.com>]

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.
---
 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 bef3165e691..6686498d7cc 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 = true)
 {
   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_NORESTORE:
 	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 704bc75b0e7..ab08e65eedc 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_NORESTORE)
+
 /* 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.  */
-- 
2.38.1