Compiling the attached test case with -O2 using the trunk compiler,
the compiler will ICE. The proposed patch is also attached. The test
is under going, but I like to have discussion on the right fix first.
thanks,
David
Analysis:
-------------
Here is what is happening:
BB6 : (Successor: BB8)
MEM_19 = phi(MEM_24, MEM_25)
t_9 = operator new (100)@MEM_19 (--> MEM_26)
mem_ref(pp_6, -16).x@MEM_26 = t_9 (-->MEM_27) --> (1)
BB8:
...
MEM_20 = PHI(MEM_27, MEM_24)
....
d.2348_15 = mem_ref(pp_6, -16).x@MEM_20
In the loop header BB3 (which dominates BB6 and BB8),
BB3:
..
pp_31 = phi (pp_6, 0);
...
pp_6 = pp_31 + 16
In PRE, ANTIC_IN(BB8) includes mem_ref(pp_31,0),x@MEM_20. After phi
translate, ANTIC_OUT(BB6) gets mem_ref(pp_31,0).x@MEM_27. However
this expression gets propagated into ANTIC_IN(BB6) even though the
memory expression is killed by (1). The root cause is that the alias
oracle reports that mem_ref(pp_6, -16) and mem_ref(pp_31, 0) are not
aliased as their points-to set do not intersect.
As as consequence of the bad aliasing, the operator new calls gets
transformed into an gimple assignment -- this gimple assignment
becomes the defining statement for MEM_26. In a later UD chain walk,
the memory chain stops (and triggers the assert) at this new
assignment statement because there is no associated vuse for it.
Test case
--------------
The case is synthesized -- the real world examples involve lots of inlining etc.
int g, *gp[100];
struct V {
int* x;
int y;
};
void foo (V **p, V* end, int i)
{
*p = 0;
V* pp = *p;
int s = 100;
for (; pp < end; )
{
pp++;
(pp-1)->x = &g;
if (g)
{
if (g>10)
g++;
int *t = (int*) operator new (100);
(pp-1)->x = t;
}
else
s--;
gp[end-pp] = (pp-1)->x + s;
}
}
Patch
---------
Index: tree-ssa-structalias.c
===================================================================
--- tree-ssa-structalias.c (revision 186600)
+++ tree-ssa-structalias.c (working copy)
@@ -6137,6 +6137,9 @@ pt_solutions_intersect_1 (struct pt_solu
if (pt1->anything || pt2->anything)
return true;
+ if (pt1->null && pt2->null)
+ return true;
+
/* If either points to unknown global memory and the other points to
any global memory they alias. */
if ((pt1->nonlocal
