[Bug tree-optimization/39612] [6/7/8 Regression] LIM inserts loads from uninitialized local memory

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39612

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |aldyh at gcc dot gnu.org

--- Comment #29 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #11)
> Re-confirmed on trunk with the testcase in comment #4 and -Os:
> 
> > ./cc1 -quiet t.c -Os -Wall -fdump-tree-all
> t.c: In function 'f2':
> t.c:4:11: warning: 'inter[0]' is used uninitialized in this function
> [-Wuninitialized]
> t.c:4:11: warning: 'inter[1]' is used uninitialized in this function
> [-Wuninitialized]
> 
> There is also a store data-race introduced by LIM when the loop header
> is not copied.  I suppose the real fix is to disable SM if the loop
> header is not copied.

The warning is gone for the testcase in comment #4:

abulafia:/build/t/gcc$ ./cc1 b.c -Os -Wall -quiet -fdump-tree-all
abulafia:/build/t/gcc$ ./cc1 b.c -O2 -Wall -quiet -fdump-tree-all

But the load from maybe-uninitialized memory is still there.  This is lim2:

f2 (int * dst, int R)
{
  _Bool inter_I_lsm.3;
  int inter_I_lsm.2;
  _Bool inter_I_lsm.1;
  int inter_I_lsm.0;
  int inter[2];
  int i;

  <bb 2> [local count: 118111601]:
  inter_I_lsm.0_16 = inter[0];         // unconditional load outside loop
  inter_I_lsm.1_17 = 0;
  inter_I_lsm.2_18 = inter[1];         // unconditional load outside loop
  inter_I_lsm.3_19 = 0;
  goto <bb 4>; [100.00%]

Reconfirmed, I guess?