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bootstrap/102681 - properly CSE PHIs with default def args

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The PR shows that we fail to CSE PHIs containing (different)
default definitions due to the fact on how we now handle
on-demand build of VN_INFO.  The following fixes this in the
same way the PHI visitation code does.

On gcc.dg/ubsan/pr81981.c this causes one expected warning to be
elided since the uninit pass sees the change

   <bb 4> [local count: 1073741824]:
   # u$0_2 = PHI <u$0_5(D)(3), i_3(D)(5)>
-  # cstore_11 = PHI <t$0_6(D)(3), i_3(D)(5)>
   v = u$0_2;
-  return cstore_11;
+  return u$0_2;

and thus only one of the conditionally uninitialized uses (the
other became dead).  I have XFAILed the missing diagnostic,
I don't see a way to preserve that.

2021-10-22  Richard Biener  <rguenther@suse.de>

	PR bootstrap/102681
	* tree-ssa-sccvn.c (vn_phi_insert): For undefined SSA args
	record VN_TOP.
	(vn_phi_lookup): Likewise.

	* gcc.dg/tree-ssa/ssa-fre-97.c: New testcase.
	* gcc.dg/ubsan/pr81981.c: XFAIL one case.
This commit is contained in:
Richard Biener 2021-10-22 10:32:36 +02:00
parent ae5c540662
commit fe8475c500
3 changed files with 32 additions and 3 deletions
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19
gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-97.c Normal file
View file

@ -0,0 +1,19 @@
/* { dg-do compile } */
/* ethread threading does not yet catch this but it might at some point. */
/* { dg-options "-O -fdump-tree-fre1-details -fno-thread-jumps" } */
int foo (int b, int x)
{
int i, j;
if (b)
i = x;
if (b)
j = x;
return j == i;
}
/* Even with different undefs we should CSE a PHI node with the
same controlling condition. */
/* { dg-final { scan-tree-dump "Replaced redundant PHI node" "fre1" } } */
/* { dg-final { scan-tree-dump "return 1;" "fre1" } } */

2
gcc/testsuite/gcc.dg/ubsan/pr81981.c
View file

@ -16,6 +16,6 @@ foo (int i)
u[0] = i;
}
v = u[0]; /* { dg-warning "may be used uninitialized" } */
v = u[0]; /* { dg-warning "may be used uninitialized" "" { xfail *-*-* } } */
return t[0]; /* { dg-warning "may be used uninitialized" } */
}

14
gcc/tree-ssa-sccvn.c
View file

@ -4499,7 +4499,12 @@ vn_phi_lookup (gimple *phi, bool backedges_varying_p)
tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
if (TREE_CODE (def) == SSA_NAME
&& (!backedges_varying_p || !(e->flags & EDGE_DFS_BACK)))
def = SSA_VAL (def);
{
if (ssa_undefined_value_p (def, false))
def = VN_TOP;
else
def = SSA_VAL (def);
}
vp1->phiargs[e->dest_idx] = def;
}
vp1->type = TREE_TYPE (gimple_phi_result (phi));
@ -4543,7 +4548,12 @@ vn_phi_insert (gimple *phi, tree result, bool backedges_varying_p)
tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
if (TREE_CODE (def) == SSA_NAME
&& (!backedges_varying_p || !(e->flags & EDGE_DFS_BACK)))
def = SSA_VAL (def);
{
if (ssa_undefined_value_p (def, false))
def = VN_TOP;
else
def = SSA_VAL (def);
}
vp1->phiargs[e->dest_idx] = def;
}
vp1->value_id = VN_INFO (result)->value_id;