Add missing cases to vect_get_smallest_scalar_type (PR 85286)

In this PR we used WIDEN_SUM_EXPR to vectorise:

  short i, y;
  int sum;
  [...]
  for (i = x; i > 0; i--)
    sum += y;

with 4 ints and 8 shorts per vector.  The problem was that we set
the VF based only on the ints, then calculated the number of vector
copies based on the shorts, giving 4/8.  Previously that led to
ncopies==0, but after r249897 we pick it up as an ICE.

In this particular case we could vectorise the reduction by setting
ncopies based on the output type rather than the input type, but it
doesn't seem worth adding a special "optimisation" for such a
pathological case.  I think it's really an instance of the more general
problem that we can't vectorise using combinations of (say) 64-bit and
128-bit vectors on targets that support both.

2018-04-10  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	PR tree-optimization/85286
	* tree-vect-data-refs.c (vect_get_smallest_scalar_type):

gcc/testsuite/
	PR tree-optimization/85286
	* gcc.dg/vect/pr85286.c: New test.

From-SVN: r259268

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 50484fa..4958959 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,10 @@
 2018-04-10  Richard Sandiford  <richard.sandiford@linaro.org>
 
+       PR tree-optimization/85286
+       * tree-vect-data-refs.c (vect_get_smallest_scalar_type):
+
+2018-04-10  Richard Sandiford  <richard.sandiford@linaro.org>
+
        * final.c (final_1): Set insn_last_address as well as
        insn_current_address.
 

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f7ca834..3cfc12c 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2018-04-10  Richard Sandiford  <richard.sandiford@linaro.org>
+
+       PR tree-optimization/85286
+       * gcc.dg/vect/pr85286.c: New test.
+
 2018-04-10  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
        PR target/85173

diff --git a/gcc/testsuite/gcc.dg/vect/pr85286.c b/gcc/testsuite/gcc.dg/vect/pr85286.c
new file mode 100644 (file)
index 0000000..320ed6b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr85286.c
@@ -0,0 +1,19 @@
+/* PR tree-optimization/45241 */
+/* { dg-do compile } */
+/* { dg-additional-options "--param scev-max-expr-complexity=0" } */
+
+int
+foo (short x)
+{
+  short i, y;
+  int sum;
+
+  for (i = 0; i < x; i++)
+    y = x * i;
+
+  for (i = x; i > 0; i--)
+    sum += y;
+
+  return sum;
+}
+

diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
index ce24387..161a886 100644 (file)
--- a/gcc/tree-vect-data-refs.c
+++ b/gcc/tree-vect-data-refs.c
@@ -132,6 +132,8 @@ vect_get_smallest_scalar_type (gimple *stmt, HOST_WIDE_INT *lhs_size_unit,
 
   if (is_gimple_assign (stmt)
       && (gimple_assign_cast_p (stmt)
+          || gimple_assign_rhs_code (stmt) == DOT_PROD_EXPR
+          || gimple_assign_rhs_code (stmt) == WIDEN_SUM_EXPR
           || gimple_assign_rhs_code (stmt) == WIDEN_MULT_EXPR
           || gimple_assign_rhs_code (stmt) == WIDEN_LSHIFT_EXPR
           || gimple_assign_rhs_code (stmt) == FLOAT_EXPR))