On August 30, 2017 7:22:45 PM GMT+02:00, Bill Schmidt
<wschm...@linux.vnet.ibm.com> wrote:
>Hi,
>
>https://gcc.gnu.org/PR81987 identifies an SSA verification error
>following
>SLSR. The problem arises when SLSR places an initialization expression
>at
>a point not dominated by the definition of an SSA name it uses. When
>there
>are multiple conditional candidates for replacement, the initialization
>expression must dominate all of these candidates and their phi
>dependencies,
>but the nearest common dominator for these may actually be above the
>stride
>definition in some cases.
>
>In such cases a single initialization point is not possible. With
>sufficient
>analysis, it would be possible to find multiple initialization points
>that
>would satisfy availability of the stride at the cost of larger code.
>This
>is too complex for a bug fix, though. This patch instead refuses to
>replace
>candidates where a single legal initialization point isn't possible.
>We
>ensure this by setting the cost for the increment associated with this
>initialization to effectively infinite.
>
>Bootstrapped and tested on powerpc64le-linux-gnu with no regressions.
>Is
>this okay for trunk, and backport to all supported releases after a
>period
>of burn-in?
Yes.
Thanks,
Richard.
>Thanks,
>Bill
>
>
>[gcc]
>
>2017-08-30 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>
> PR tree-optimization/81987
> * gimple-ssa-strength-reduction.c (insert_initializers): Don't
> insert an initializer in a location not dominated by the stride
> definition.
>
>[gcc/testsuite]
>
>2017-08-30 Bill Schmidt <wschm...@linux.vnet.ibm.com>
>
> PR tree-optimization/81987
> * g++.dg/torture/pr81987.C: New file.
>
>
>Index: gcc/gimple-ssa-strength-reduction.c
>===================================================================
>--- gcc/gimple-ssa-strength-reduction.c (revision 251369)
>+++ gcc/gimple-ssa-strength-reduction.c (working copy)
>@@ -3340,6 +3340,23 @@ insert_initializers (slsr_cand_t c)
> that block, the earliest one will be returned in WHERE. */
> bb = nearest_common_dominator_for_cands (c, incr, &where);
>
>+ /* If the NCD is not dominated by the block containing the
>+ definition of the stride, we can't legally insert a
>+ single initializer. Mark the increment as unprofitable
>+ so we don't make any replacements. FIXME: Multiple
>+ initializers could be placed with more analysis. */
>+ gimple *stride_def = SSA_NAME_DEF_STMT (c->stride);
>+ basic_block stride_bb = gimple_bb (stride_def);
>+
>+ if (stride_bb && !dominated_by_p (CDI_DOMINATORS, bb,
>stride_bb))
>+ {
>+ if (dump_file && (dump_flags & TDF_DETAILS))
>+ fprintf (dump_file,
>+ "Initializer #%d cannot be legally placed\n", i);
>+ incr_vec[i].cost = COST_INFINITE;
>+ continue;
>+ }
>+
> /* If the nominal stride has a different type than the recorded
> stride type, build a cast from the nominal stride to that type. */
> if (!types_compatible_p (TREE_TYPE (c->stride), c->stride_type))
>Index: gcc/testsuite/g++.dg/torture/pr81987.C
>===================================================================
>--- gcc/testsuite/g++.dg/torture/pr81987.C (nonexistent)
>+++ gcc/testsuite/g++.dg/torture/pr81987.C (working copy)
>@@ -0,0 +1,61 @@
>+extern short var_1;
>+extern const short var_3;
>+extern unsigned long int var_9;
>+extern short var_13;
>+extern const unsigned long int var_15;
>+extern const unsigned long int var_37;
>+extern unsigned long int var_40;
>+extern long long int var_47;
>+extern short var_48;
>+extern const short var_54;
>+extern long long int var_79;
>+extern long long int var_81;
>+extern long long int var_94;
>+extern long long int var_95;
>+extern long long int var_701;
>+extern unsigned long int var_786;
>+extern short var_788;
>+extern long long int var_844;
>+
>+struct struct_1 {
>+ short member_1_2 : 15;
>+ static long long int member_1_3;
>+};
>+
>+extern struct_1 struct_obj_6;
>+extern struct_1 struct_obj_8;
>+
>+void foo() {
>+ int a = var_3 <= 602154393864UL;
>+ if (var_81 ? 0 : var_3 && var_9)
>+ ;
>+ else {
>+ var_94 = 0;
>+ if (var_3 && var_48 || var_13) {
>+ if (var_48)
>+ var_95 = 0;
>+ short b((2364461588881776511UL + var_3) * (2 ? var_13 : 0) ||
>var_1);
>+ struct_obj_8.member_1_2 = b;
>+ if (var_15) {
>+ if (var_81)
>+ if (var_47)
>+ ;
>+ else if (var_40)
>+ var_701 = 0;
>+ } else {
>+ if (var_40)
>+ var_79 = 0;
>+ if (var_54) {
>+ if (var_37)
>+ var_786 = 0;
>+ else
>+ var_788 = 0;
>+ struct_obj_6.member_1_3 =
>+ (2364461588881776511UL + var_3) * (2 ? var_13 : 0);
>+ }
>+ }
>+ if ((2364461588881776511UL + var_3) * (2 ? var_13 : 0))
>+ var_844 = 0;
>+ }
>+ }
>+}
