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var-tracking.c: Fix possible use of uninitialized variable pre

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While bootstrapping GCC on S/390 the following warning/error is raised:

gcc/var-tracking.c:10239:34: error: 'pre' may be used uninitialized in this function [-Werror=maybe-uninitialized]
10239 |       VTI (bb)->out.stack_adjust += pre;
      |                                  ^

The lines of interest are:

  HOST_WIDE_INT pre, post = 0;
  // ...
  if (!frame_pointer_needed)
    {
      insn_stack_adjust_offset_pre_post (insn, &pre, &post);
      // ...
    }

  // ...
  adjust_insn (bb, insn);

  if (!frame_pointer_needed && pre)
    VTI (bb)->out.stack_adjust += pre;

Both if statements depend on global variable frame_pointer_needed.  In function
insn_stack_adjust_offset_pre_post local variable pre is initialized.  The
problematic part is the function call between both if statements.  Since
adjust_insn also calls functions which are defined in a different compilation
unit, we are not able to prove that global variable frame_pointer_needed is not
altered by adjust_insn and its siblings.  Thus we must assume that
frame_pointer_needed may be true before the call and false afterwards which
renders the warning true (admitted the location hint is not totally perfect).
By initialising pre we silence the warning.

gcc/ChangeLog:

2020-04-30  Stefan Schulze Frielinghaus  <stefansf@linux.ibm.com>

        * var-tracking.c (vt_initialize): Move variables pre and post
        into inner block and initialize both in order to fix warning
        about uninitialized use.  Remove unnecessary checks for
        frame_pointer_needed.
This commit is contained in:
Stefan Schulze Frielinghaus 2020-04-26 17:10:51 +02:00
parent 3c9450bf5c
commit 2786c0221b
2 changed files with 11 additions and 3 deletions
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7
gcc/ChangeLog
View File

@ -1,3 +1,10 @@
2020-04-30 Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>
* var-tracking.c (vt_initialize): Move variables pre and post
into inner block and initialize both in order to fix warning
about uninitialized use. Remove unnecessary checks for
frame_pointer_needed.
2020-04-30 Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>
* toplev.c (output_stack_usage_1): Ensure that first

7
gcc/var-tracking.c
View File

@ -10171,7 +10171,6 @@ vt_initialize (void)
FOR_EACH_BB_FN (bb, cfun)
{
rtx_insn *insn;
HOST_WIDE_INT pre, post = 0;
basic_block first_bb, last_bb;
if (MAY_HAVE_DEBUG_BIND_INSNS)
@ -10216,6 +10215,8 @@ vt_initialize (void)
{
if (INSN_P (insn))
{
HOST_WIDE_INT pre = 0, post = 0;
if (!frame_pointer_needed)
{
insn_stack_adjust_offset_pre_post (insn, &pre, &post);
@ -10235,7 +10236,7 @@ vt_initialize (void)
cselib_hook_called = false;
adjust_insn (bb, insn);
if (!frame_pointer_needed && pre)
if (pre)
VTI (bb)->out.stack_adjust += pre;
if (DEBUG_MARKER_INSN_P (insn))
@ -10262,7 +10263,7 @@ vt_initialize (void)
add_with_sets (insn, 0, 0);
cancel_changes (0);
if (!frame_pointer_needed && post)
if (post)
{
micro_operation mo;
mo.type = MO_ADJUST;