[debug] Fix pre_dec handling in vartrack

When compiling test-case gcc.target/i386/vartrack-1.c with -O1 -g, register bx
is pushed in the prologue and popped in the epilogue:
...
(insn/f 26 3 27 2
  (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [0  S8 A8])
       (reg:DI 3 bx))
   "vartrack-1.c":10 61 {*pushdi2_rex64}
   (expr_list:REG_DEAD (reg:DI 3 bx) (nil)))
  ...
(insn/f 29 28 30 2
  (set (reg:DI 3 bx)
       (mem:DI (post_inc:DI (reg/f:DI 7 sp)) [0  S8 A8]))
   "vartrack-1.c":15 71 {*popdi1}
   (expr_list:REG_CFA_ADJUST_CFA
     (set (reg/f:DI 7 sp)
          (plus:DI (reg/f:DI 7 sp)
                   (const_int 8 [0x8]))) (nil)))
...

However, when we adjust those insns in vartrack to eliminate the pre_dec and
post_inc, the frame location for the push is at argp - 24, while the one for the
pop is at argp - 16:
...
(insn/f 26 3 27 2
  (parallel [
    (set (mem:DI (plus:DI (reg/f:DI 16 argp)
                          (const_int -24 [0xffffffffffffffe8])) [0  S8 A8])
         (reg:DI 3 bx))
    (set (reg/f:DI 7 sp)
         (plus:DI (reg/f:DI 16 argp)
                  (const_int -24 [0xffffffffffffffe8])))
  ])
  "vartrack-1.c":10 61 {*pushdi2_rex64}
  (expr_list:REG_DEAD (reg:DI 3 bx) (nil)))
  ...
(insn/f 29 28 30 2
  (parallel [
    (set (reg:DI 3 bx)
         (mem:DI (plus:DI (reg/f:DI 16 argp)
                          (const_int -16 [0xfffffffffffffff0])) [0  S8 A8]))
    (set (reg/f:DI 7 sp)
         (plus:DI (reg/f:DI 16 argp)
                  (const_int -8 [0xfffffffffffffff8])))
  ])
  "vartrack-1.c":15 71 {*popdi1}
  (expr_list:REG_CFA_ADJUST_CFA
    (set (reg/f:DI 7 sp)
         (plus:DI (reg/f:DI 7 sp)
                  (const_int 8 [0x8]))) (nil)))
...

This patch fixes that by moving the stack_adjust modification after
adjust_insn in vt_initialize.

Bootstrapped and reg-tested on x86_64.

2018-07-16  Tom de Vries  <tdevries@suse.de>

	PR debug/86455
	* var-tracking.c (vt_initialize): Fix pre_dec handling.

	* gcc.target/i386/vartrack-1.c: New test.

From-SVN: r262687

gcc/ChangeLog

+2018-07-16  Tom de Vries  <tdevries@suse.de>
+
+	PR debug/86455
+	* var-tracking.c (vt_initialize): Fix pre_dec handling.
+
 2018-07-16  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
 
 	* config/aarch64/atomics.md (aarch64_store_execlusive<mode>): Add

gcc/testsuite/ChangeLog

+2018-07-16  Tom de Vries  <tdevries@suse.de>
+
+	PR debug/86455
+	* gcc.target/i386/vartrack-1.c: New test.
+
 2018-07-16  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gnat.dg/opt73.adb: New test.

gcc/testsuite/gcc.target/i386/vartrack-1.c

+/* { dg-require-effective-target lp64 } */
+/* { dg-options "-O1 -g -fdump-rtl-vartrack-details-slim" } */
+
+static volatile int vv = 1;
+
+extern long foo (long x);
+
+int
+main ()
+{
+  long x = vv;
+  foo (x);
+  foo (x + 1);
+  return 0;
+}
+
+/* Before adjust_insn:
+   26: [--sp:DI]=bx:DI
+   29: bx:DI=[sp:DI++]
+
+   after adjust_insn:
+   26: {[argp:DI-0x10]=bx:DI;sp:DI=argp:DI-0x10;}
+   29: {bx:DI=[argp:DI-0x10];sp:DI=argp:DI-0x8;} */
+
+/* { dg-final { scan-rtl-dump-times {[0-9][0-9]*: \{\[argp:DI-0x10\]=bx:DI;sp:DI=argp:DI-0x10;\}} 1 "vartrack" } } */
+
+/* { dg-final { scan-rtl-dump-times {[0-9][0-9]*: \{bx:DI=\[argp:DI-0x10\];sp:DI=argp:DI-0x8;\}} 1 "vartrack" } } */
+

gcc/var-tracking.c

@@ -10209,12 +10209,15 @@ vt_initialize (void)
 			    log_op_type (PATTERN (insn), bb, insn,
 					 MO_ADJUST, dump_file);
 			  VTI (bb)->mos.safe_push (mo);
-			  VTI (bb)->out.stack_adjust += pre;
 			}
 		    }
 
 		  cselib_hook_called = false;
 		  adjust_insn (bb, insn);
+
+		  if (!frame_pointer_needed && pre)
+		    VTI (bb)->out.stack_adjust += pre;
+
 		  if (DEBUG_MARKER_INSN_P (insn))
 		    {
 		      reemit_marker_as_note (insn);