This fixes PR56661 - we were value-numbering two call results
the same even though function attributes tell us that they are
required to return a distinct value (and this property is exploited
by alias analysis). Simply don't do that (as opposed to trying to
fix things up).
Bootstrap and regtest pending on x86_64-unknown-linux-gnu.
Richard.
2013-03-20 Richard Biener <rguent...@suse.de>
PR tree-optimization/56661
* tree-ssa-sccvn.c (visit_use): Only value-number calls if
the result does not have to be distinct.
* gcc.dg/torture/pr56661.c: New testcase.
Index: gcc/tree-ssa-sccvn.c
===================================================================
*** gcc/tree-ssa-sccvn.c (revision 196808)
--- gcc/tree-ssa-sccvn.c (working copy)
*************** visit_use (tree use)
*** 3506,3513 ****
We can value number 2 calls to the same function with the
same vuse and the same operands which are not subsequent
the same, because there is no code in the program that can
! compare the 2 values. */
! || gimple_vdef (stmt)))
changed = visit_reference_op_call (lhs, stmt);
else
changed = defs_to_varying (stmt);
--- 3506,3518 ----
We can value number 2 calls to the same function with the
same vuse and the same operands which are not subsequent
the same, because there is no code in the program that can
! compare the 2 values... */
! || (gimple_vdef (stmt)
! /* ... unless the call returns a pointer which does
! not alias with anything else. In which case the
! information that the values are distinct are encoded
! in the IL. */
! && !(gimple_call_return_flags (stmt) & ERF_NOALIAS))))
changed = visit_reference_op_call (lhs, stmt);
else
changed = defs_to_varying (stmt);
Index: gcc/testsuite/gcc.dg/torture/pr56661.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr56661.c (revision 0)
--- gcc/testsuite/gcc.dg/torture/pr56661.c (working copy)
***************
*** 0 ****
--- 1,46 ----
+ /* { dg-do run } */
+
+ __attribute__((noinline, noclone)) void
+ bar (int *b)
+ {
+ b[0] = b[1] = b[2] = 1;
+ }
+
+ __attribute__((noinline, noclone)) int
+ baz (int x)
+ {
+ if (x != 1)
+ __builtin_abort ();
+ }
+
+ void
+ foo (int x)
+ {
+ if (x == 0)
+ {
+ int *b = __builtin_malloc (3 * sizeof (int));
+ while (b[0])
+ ;
+ }
+ else if (x == 1)
+ {
+ int i, j;
+ int *b = __builtin_malloc (3 * sizeof (int));
+ for (i = 0; i < 2; i++)
+ {
+ bar (b);
+ for (j = 0; j < 3; ++j)
+ baz (b[j]);
+ baz (b[0]);
+ }
+ }
+ }
+
+ int
+ main ()
+ {
+ int x = 1;
+ asm volatile ("" : "+r" (x));
+ foo (x);
+ return 0;
+ }
