On Mon, 17 Dec 2012, Richard Biener wrote:
>
> The following patch fixes a miscompilation due to bogus loop iteration
> bound derived from array accesses in an inner loop. idx_infer_loop_bounds
> analyzes the evoultion of an SSA name with respect to a loop it is not
> defined in - which seems to lead to random weird behavior. The correct
> thing to do (as documented) is to analyze the evolution with respect
> to the loop the stmt we are interested in is in.
>
> Bootstrap and regtest ongoing on x86_64-unknown-linux-gnu.
Which shows that the very old fix for PR40281 isn't complete
(the patch regresses PR55687 again). So the following extends
that fix. I wonder whether we instead want to pass down
CHREC_VARIABLE and avoid doing the instantiation in the first
place ...
Bootstrap and regtest ongoing on x86_64-unknown-linux-gnu.
Comments welcome.
Thanks,
Richard.
2012-12-17 Richard Biener <rguent...@suse.de>
PR tree-optimization/55555
* tree-ssa-loop-niter.c (idx_infer_loop_bounds): Properly
analyze evolution of the index for the loop it is used in.
* tree-scalar-evolution.c (instantiate_scev_poly): Generalize
fix for PR40281 and prune invalid SCEVs.
* gcc.dg/torture/pr55555.c: New testcase.
Index: gcc/tree-ssa-loop-niter.c
===================================================================
*** gcc/tree-ssa-loop-niter.c (revision 194552)
--- gcc/tree-ssa-loop-niter.c (working copy)
*************** idx_infer_loop_bounds (tree base, tree *
*** 2671,2677 ****
upper = false;
}
! ev = instantiate_parameters (loop, analyze_scalar_evolution (loop, *idx));
init = initial_condition (ev);
step = evolution_part_in_loop_num (ev, loop->num);
--- 2671,2682 ----
upper = false;
}
! struct loop *dloop = loop_containing_stmt (data->stmt);
! if (!dloop)
! return true;
!
! ev = analyze_scalar_evolution (dloop, *idx);
! ev = instantiate_parameters (loop, ev);
init = initial_condition (ev);
step = evolution_part_in_loop_num (ev, loop->num);
Index: gcc/tree-scalar-evolution.c
===================================================================
*** gcc/tree-scalar-evolution.c (revision 194552)
--- gcc/tree-scalar-evolution.c (working copy)
*************** instantiate_scev_poly (basic_block insta
*** 2268,2295 ****
if (op0 == chrec_dont_know)
return chrec_dont_know;
op1 = instantiate_scev_r (instantiate_below, evolution_loop,
CHREC_RIGHT (chrec), fold_conversions, cache,
size_expr);
if (op1 == chrec_dont_know)
return chrec_dont_know;
! if (CHREC_LEFT (chrec) != op0
! || CHREC_RIGHT (chrec) != op1)
{
! unsigned var = CHREC_VARIABLE (chrec);
!
! /* When the instantiated stride or base has an evolution in an
! innermost loop, return chrec_dont_know, as this is not a
! valid SCEV representation. In the reduced testcase for
! PR40281 we would have {0, +, {1, +, 1}_2}_1 that has no
! meaning. */
! if ((tree_is_chrec (op0) && CHREC_VARIABLE (op0) > var)
! || (tree_is_chrec (op1) && CHREC_VARIABLE (op1) > var))
return chrec_dont_know;
op1 = chrec_convert_rhs (chrec_type (op0), op1, NULL);
! chrec = build_polynomial_chrec (var, op0, op1);
}
return chrec;
--- 2268,2322 ----
if (op0 == chrec_dont_know)
return chrec_dont_know;
+ /* When the instantiated stride or base has an evolution in an
+ innermost loop, return chrec_dont_know, as this is not a
+ valid SCEV representation. In the reduced testcase for
+ PR40281 we would have {0, +, {1, +, 1}_2}_1 that has no
+ meaning. */
+ if (tree_does_not_contain_chrecs (op0))
+ ;
+ else
+ {
+ tree tem = op0;
+ while (TREE_CODE (tem) != POLYNOMIAL_CHREC)
+ {
+ if (CONVERT_EXPR_P (tem))
+ tem = TREE_OPERAND (tem, 0);
+ else
+ return chrec_dont_know;
+ }
+ if (!flow_loop_nested_p (get_chrec_loop (tem), get_chrec_loop (chrec)))
+ return chrec_dont_know;
+ }
+
op1 = instantiate_scev_r (instantiate_below, evolution_loop,
CHREC_RIGHT (chrec), fold_conversions, cache,
size_expr);
if (op1 == chrec_dont_know)
return chrec_dont_know;
! /* See above. */
! if (tree_does_not_contain_chrecs (op1))
! ;
! else
{
! tree tem = op1;
! while (TREE_CODE (tem) != POLYNOMIAL_CHREC)
! {
! if (CONVERT_EXPR_P (tem))
! tem = TREE_OPERAND (tem, 0);
! else
! return chrec_dont_know;
! }
! if (!flow_loop_nested_p (get_chrec_loop (tem), get_chrec_loop (chrec)))
return chrec_dont_know;
+ }
+ if (CHREC_LEFT (chrec) != op0
+ || CHREC_RIGHT (chrec) != op1)
+ {
op1 = chrec_convert_rhs (chrec_type (op0), op1, NULL);
! chrec = build_polynomial_chrec (CHREC_VARIABLE (chrec), op0, op1);
}
return chrec;
Index: gcc/testsuite/gcc.dg/torture/pr55555.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr55555.c (revision 0)
--- gcc/testsuite/gcc.dg/torture/pr55555.c (working copy)
***************
*** 0 ****
--- 1,34 ----
+ /* { dg-do run } */
+
+ double s[4] = { 1.0, 2.0, 3.0, 4.0 }, pol_x[2] = { 5.0, 6.0 };
+
+ __attribute__((noinline)) int
+ foo (void)
+ {
+ double coef_x[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
+ int lxp = 0;
+ if (lxp <= 1)
+ do
+ {
+ double t = pol_x[lxp];
+ long S;
+ long l = lxp * 4L - 1;
+ for (S = 1; S <= 4; S++)
+ coef_x[S + l] = coef_x[S + l] + s[S - 1] * t;
+ }
+ while (lxp++ != 1);
+ asm volatile ("" : : "r" (coef_x) : "memory");
+ for (lxp = 0; lxp < 8; lxp++)
+ if (coef_x[lxp] != ((lxp & 3) + 1) * (5.0 + (lxp >= 4)))
+ __builtin_abort ();
+ return 1;
+ }
+
+ int
+ main ()
+ {
+ asm volatile ("" : : : "memory");
+ if (!foo ())
+ __builtin_abort ();
+ return 0;
+ }
