This patch simplifies the handling of EH return.

This patch simplifies the handling of EH return.  We force the use of the
frame pointer so the return location is always at FP + 8.  This means we
can emit a simple volatile access in EH_RETURN_HANDLER_RTX without needing md
patterns, splitters and frame offset calculations.  The new implementation also
fixes various bugs in aarch64_final_eh_return_addr, which does not work with
-fomit-frame-pointer, alloca or outgoing arguments.

    gcc/
	* config/aarch64/aarch64.md (eh_return): Remove pattern and splitter.
	* config/aarch64/aarch64.h (AARCH64_EH_STACKADJ_REGNUM): Remove.
	(EH_RETURN_HANDLER_RTX): New define.
	* config/aarch64/aarch64.c (aarch64_frame_pointer_required):
	Force frame pointer in EH return functions.
	(aarch64_expand_epilogue): Add barrier for eh_return.
	(aarch64_final_eh_return_addr): Remove.
	(aarch64_eh_return_handler_rtx): New function.
	* config/aarch64/aarch64-protos.h (aarch64_final_eh_return_addr):
	Remove.
	(aarch64_eh_return_handler_rtx): New prototype.

    testsuite/
	* gcc.target/aarch64/eh_return.c: New test.

From-SVN: r244547

gcc/ChangeLog

+2017-01-17  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* config/aarch64/aarch64.md (eh_return): Remove pattern and splitter.
+	* config/aarch64/aarch64.h (AARCH64_EH_STACKADJ_REGNUM): Remove.
+	(EH_RETURN_HANDLER_RTX): New define.
+	* config/aarch64/aarch64.c (aarch64_frame_pointer_required):
+	Force frame pointer in EH return functions.
+	(aarch64_expand_epilogue): Add barrier for eh_return.
+	(aarch64_final_eh_return_addr): Remove.
+	(aarch64_eh_return_handler_rtx): New function.
+	* config/aarch64/aarch64-protos.h (aarch64_final_eh_return_addr):
+	Remove.
+	(aarch64_eh_return_handler_rtx): New prototype.
+
 2017-01-17  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* config/rs6000/altivec.h (vec_rlmi): New #define.

gcc/config/aarch64/aarch64-protos.h

@@ -358,7 +358,7 @@ int aarch64_hard_regno_mode_ok (unsigned, machine_mode);
 int aarch64_hard_regno_nregs (unsigned, machine_mode);
 int aarch64_uxt_size (int, HOST_WIDE_INT);
 int aarch64_vec_fpconst_pow_of_2 (rtx);
-rtx aarch64_final_eh_return_addr (void);
+rtx aarch64_eh_return_handler_rtx (void);
 rtx aarch64_mask_from_zextract_ops (rtx, rtx);
 const char *aarch64_output_move_struct (rtx *operands);
 rtx aarch64_return_addr (int, rtx);

gcc/config/aarch64/aarch64.c

@@ -2762,6 +2762,10 @@ aarch64_frame_pointer_required (void)
       && (!crtl->is_leaf || df_regs_ever_live_p (LR_REGNUM)))
     return true;
 
+  /* Force a frame pointer for EH returns so the return address is at FP+8.  */
+  if (crtl->calls_eh_return)
+    return true;
+
   return false;
 }
 
@@ -3620,7 +3624,8 @@ aarch64_expand_epilogue (bool for_sibcall)
 			 + cfun->machine->frame.saved_varargs_size) != 0;
 
   /* Emit a barrier to prevent loads from a deallocated stack.  */
-  if (final_adjust > crtl->outgoing_args_size || cfun->calls_alloca)
+  if (final_adjust > crtl->outgoing_args_size || cfun->calls_alloca
+      || crtl->calls_eh_return)
     {
       emit_insn (gen_stack_tie (stack_pointer_rtx, stack_pointer_rtx));
       need_barrier_p = false;
@@ -3688,52 +3693,40 @@ aarch64_expand_epilogue (bool for_sibcall)
     emit_jump_insn (ret_rtx);
 }
 
-/* Return the place to copy the exception unwinding return address to.
-   This will probably be a stack slot, but could (in theory be the
-   return register).  */
-rtx
-aarch64_final_eh_return_addr (void)
-{
-  HOST_WIDE_INT fp_offset;
-
-  aarch64_layout_frame ();
+/* Implement EH_RETURN_HANDLER_RTX.  EH returns need to either return
+   normally or return to a previous frame after unwinding.
 
-  fp_offset = cfun->machine->frame.frame_size
-	      - cfun->machine->frame.hard_fp_offset;
+   An EH return uses a single shared return sequence.  The epilogue is
+   exactly like a normal epilogue except that it has an extra input
+   register (EH_RETURN_STACKADJ_RTX) which contains the stack adjustment
+   that must be applied after the frame has been destroyed.  An extra label
+   is inserted before the epilogue which initializes this register to zero,
+   and this is the entry point for a normal return.
 
-  if (cfun->machine->frame.reg_offset[LR_REGNUM] < 0)
-    return gen_rtx_REG (DImode, LR_REGNUM);
+   An actual EH return updates the return address, initializes the stack
+   adjustment and jumps directly into the epilogue (bypassing the zeroing
+   of the adjustment).  Since the return address is typically saved on the
+   stack when a function makes a call, the saved LR must be updated outside
+   the epilogue.
 
-  /* DSE and CSELIB do not detect an alias between sp+k1 and fp+k2.  This can
-     result in a store to save LR introduced by builtin_eh_return () being
-     incorrectly deleted because the alias is not detected.
-     So in the calculation of the address to copy the exception unwinding
-     return address to, we note 2 cases.
-     If FP is needed and the fp_offset is 0, it means that SP = FP and hence
-     we return a SP-relative location since all the addresses are SP-relative
-     in this case.  This prevents the store from being optimized away.
-     If the fp_offset is not 0, then the addresses will be FP-relative and
-     therefore we return a FP-relative location.  */
+   This poses problems as the store is generated well before the epilogue,
+   so the offset of LR is not known yet.  Also optimizations will remove the
+   store as it appears dead, even after the epilogue is generated (as the
+   base or offset for loading LR is different in many cases).
 
-  if (frame_pointer_needed)
-    {
-      if (fp_offset)
-        return gen_frame_mem (DImode,
+   To avoid these problems this implementation forces the frame pointer
+   in eh_return functions so that the location of LR is fixed and known early.
+   It also marks the store volatile, so no optimization is permitted to
+   remove the store.  */
+rtx
+aarch64_eh_return_handler_rtx (void)
+{
+  rtx tmp = gen_frame_mem (Pmode,
     plus_constant (Pmode, hard_frame_pointer_rtx, UNITS_PER_WORD));
-      else
-        return gen_frame_mem (DImode,
-			      plus_constant (Pmode, stack_pointer_rtx, UNITS_PER_WORD));
-    }
 
-  /* If FP is not needed, we calculate the location of LR, which would be
-     at the top of the saved registers block.  */
-
-  return gen_frame_mem (DImode,
-			plus_constant (Pmode,
-				       stack_pointer_rtx,
-				       fp_offset
-				       + cfun->machine->frame.saved_regs_size
-				       - 2 * UNITS_PER_WORD));
+  /* Mark the store volatile, so no optimization is permitted to remove it.  */
+  MEM_VOLATILE_P (tmp) = true;
+  return tmp;
 }
 
 /* Output code to add DELTA to the first argument, and then jump

gcc/config/aarch64/aarch64.h

@@ -400,9 +400,9 @@ extern unsigned aarch64_architecture_version;
 #define ASM_DECLARE_FUNCTION_NAME(STR, NAME, DECL)	\
   aarch64_declare_function_name (STR, NAME, DECL)
 
-/* The register that holds the return address in exception handlers.  */
-#define AARCH64_EH_STACKADJ_REGNUM	(R0_REGNUM + 4)
-#define EH_RETURN_STACKADJ_RTX	gen_rtx_REG (Pmode, AARCH64_EH_STACKADJ_REGNUM)
+/* For EH returns X4 contains the stack adjustment.  */
+#define EH_RETURN_STACKADJ_RTX	gen_rtx_REG (Pmode, R4_REGNUM)
+#define EH_RETURN_HANDLER_RTX  aarch64_eh_return_handler_rtx ()
 
 /* Don't use __builtin_setjmp until we've defined it.  */
 #undef DONT_USE_BUILTIN_SETJMP

gcc/config/aarch64/aarch64.md

@@ -592,25 +592,6 @@
   [(set_attr "type" "branch")]
 )
 
-(define_insn "eh_return"
-  [(unspec_volatile [(match_operand:DI 0 "register_operand" "r")]
-    UNSPECV_EH_RETURN)]
-  ""
-  "#"
-  [(set_attr "type" "branch")]
-
-)
-
-(define_split
-  [(unspec_volatile [(match_operand:DI 0 "register_operand" "")]
-    UNSPECV_EH_RETURN)]
-  "reload_completed"
-  [(set (match_dup 1) (match_dup 0))]
-  {
-    operands[1] = aarch64_final_eh_return_addr ();
-  }
-)
-
 (define_insn "*cb<optab><mode>1"
   [(set (pc) (if_then_else (EQL (match_operand:GPI 0 "register_operand" "r")
 				(const_int 0))

gcc/testsuite/ChangeLog

+2017-01-17  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* gcc.target/aarch64/eh_return.c: New test.
+
 2017-01-17  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* vec-rlmi-rlnm.c: New file.

gcc/testsuite/gcc.target/aarch64/eh_return.c

+/* { dg-do run } */
+/* { dg-options "-O2 -fno-inline" } */
+
+#include <stdlib.h>
+#include <stdio.h>
+
+int val, test, failed;
+
+int main (void);
+
+void
+eh0 (void *p)
+{
+  val = (int)(long)p & 7;
+  if (val)
+    abort ();
+}
+
+void
+eh1 (void *p, int x)
+{
+  void *q = __builtin_alloca (x);
+  eh0 (q);
+  __builtin_eh_return (0, p);
+}
+
+void
+eh2a (int a,int b,int c,int d,int e,int f,int g,int h, void *p)
+{
+  val = a + b + c + d + e + f + g + h +  (int)(long)p & 7;
+}
+
+void
+eh2 (void *p)
+{
+  eh2a (val, val, val, val, val, val, val, val, p);
+  __builtin_eh_return (0, p);
+}
+
+
+void
+continuation (void)
+{
+  test++;
+  main ();
+}
+
+void
+fail (void)
+{
+  failed = 1;
+  printf ("failed\n");
+  continuation ();
+}
+
+void
+do_test1 (void)
+{
+  if (!val)
+    eh1 (continuation, 100);
+  fail ();
+}
+
+void
+do_test2 (void)
+{
+  if (!val)
+    eh2 (continuation);
+  fail ();
+}
+
+int
+main (void)
+{
+  if (test == 0)
+    do_test1 ();
+  if (test == 1)
+    do_test2 ();
+  if (failed || test != 2)
+    exit (1);
+  exit (0);
+}