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PR81815: Invalid conditional reduction
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: gcc-patches at gcc dot gnu dot org
- Date: Mon, 14 Aug 2017 13:48:03 +0100
- Subject: PR81815: Invalid conditional reduction
- Authentication-results: sourceware.org; auth=none
We weren't checking whether the phi in a conditional reduction was
used by the condition itself (which isn't a case we handle).
Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Thanks,
Richard
2017-08-11 Richard Sandiford <richard.sandiford@linaro.org>
gcc/
PR tree-optimization/81835
* tree-vect-loop.c (vect_is_simple_reduction): Simply checks for
the phi SSA_NAME. Check that the condition in a COND_EXPR does
not depend on the phi.
gcc/testsuite/
PR tree-optimization/81835
* gcc.dg/vect/pr81815.c: New test.
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c 2017-08-04 11:41:05.710206063 +0100
+++ gcc/tree-vect-loop.c 2017-08-14 13:46:28.336459006 +0100
@@ -2690,15 +2690,15 @@ vect_is_simple_reduction (loop_vec_info
*double_reduc = false;
*v_reduc_type = TREE_CODE_REDUCTION;
- name = PHI_RESULT (phi);
+ tree phi_name = PHI_RESULT (phi);
/* ??? If there are no uses of the PHI result the inner loop reduction
won't be detected as possibly double-reduction by vectorizable_reduction
because that tries to walk the PHI arg from the preheader edge which
can be constant. See PR60382. */
- if (has_zero_uses (name))
+ if (has_zero_uses (phi_name))
return NULL;
nloop_uses = 0;
- FOR_EACH_IMM_USE_FAST (use_p, imm_iter, name)
+ FOR_EACH_IMM_USE_FAST (use_p, imm_iter, phi_name)
{
gimple *use_stmt = USE_STMT (use_p);
if (is_gimple_debug (use_stmt))
@@ -2847,10 +2847,7 @@ vect_is_simple_reduction (loop_vec_info
simply rewriting this into "res += -x[i]". Avoid changing
gimple instruction for the first simple tests and only do this
if we're allowed to change code at all. */
- if (code == MINUS_EXPR
- && ! ((op1 = gimple_assign_rhs2 (def_stmt))
- && TREE_CODE (op1) == SSA_NAME
- && SSA_NAME_DEF_STMT (op1) == phi))
+ if (code == MINUS_EXPR && gimple_assign_rhs2 (def_stmt) != phi_name)
code = PLUS_EXPR;
if (code == COND_EXPR)
@@ -2864,6 +2861,14 @@ vect_is_simple_reduction (loop_vec_info
op4 = TREE_OPERAND (op3, 1);
op3 = TREE_OPERAND (op3, 0);
}
+ if (op3 == phi_name || op4 == phi_name)
+ {
+ if (dump_enabled_p ())
+ report_vect_op (MSG_MISSED_OPTIMIZATION, def_stmt,
+ "reduction: condition depends on previous"
+ " iteration: ");
+ return NULL;
+ }
op1 = gimple_assign_rhs2 (def_stmt);
op2 = gimple_assign_rhs3 (def_stmt);
Index: gcc/testsuite/gcc.dg/vect/pr81815.c
===================================================================
--- /dev/null 2017-08-14 10:10:17.469973707 +0100
+++ gcc/testsuite/gcc.dg/vect/pr81815.c 2017-08-14 13:46:28.334496436 +0100
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+
+int __attribute__ ((noinline, noclone))
+f (int *x, int n)
+{
+ int b = 13;
+ for (int i = 0; i < n; ++i)
+ {
+ int next = x[i];
+ b = b < 100 ? next : 200;
+ }
+ return b;
+}
+
+static int res[32];
+
+int
+main (void)
+{
+ for (int i = 0; i < 32; ++i)
+ res[i] = i;
+ res[15] = 100;
+ if (f (res, 32) != 200)
+ __builtin_abort ();
+ return 0;
+}