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Re: [PATCH] [vectorizer] Fixing a bug in tree-vect-patterns.c in GCC vectorizer.


A new test case is added to testsuite/gcc.dg/vect, which will fail
without this patch and pass with it. Bootstrap also get passed. No
additional test failure is introduced.

The new test case includes a dot product on two arrays with short and
int types. The loop will still be vectorized (using punpcklwd on array
with short type), but should not be recognized as a dot-product
pattern.


thanks,
Cong





Index: gcc/tree-vect-patterns.c
===================================================================
--- gcc/tree-vect-patterns.c (revision 202572)
+++ gcc/tree-vect-patterns.c (working copy)
@@ -397,7 +397,7 @@ vect_recog_dot_prod_pattern (vec<gimple>
           || !promotion)
         return NULL;
       oprnd00 = gimple_assign_rhs1 (def_stmt);
-      if (!type_conversion_p (oprnd0, stmt, true, &half_type1, &def_stmt,
+      if (!type_conversion_p (oprnd1, stmt, true, &half_type1, &def_stmt,
                                 &promotion)
           || !promotion)
         return NULL;
Index: gcc/ChangeLog
===================================================================
--- gcc/ChangeLog (revision 202572)
+++ gcc/ChangeLog (working copy)
@@ -1,3 +1,9 @@
+2013-09-13  Cong Hou  <congh@google.com>
+
+ * tree-vect-patterns.c (vect_recog_dot_prod_pattern): Fix a bug
+ when checking the dot production pattern. The type of rhs operand
+ of multiply is now checked correctly.
+
 2013-09-13  Jan Hubicka  <jh@suse.cz>

  PR middle-end/58094
Index: gcc/testsuite/gcc.dg/vect/vect-reduc-dot-s16c.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/vect-reduc-dot-s16c.c (revision 0)
+++ gcc/testsuite/gcc.dg/vect/vect-reduc-dot-s16c.c (revision 0)
@@ -0,0 +1,73 @@
+/* { dg-require-effective-target vect_int } */
+
+#include <stdarg.h>
+#include "tree-vect.h"
+
+#define N 64
+#define DOT 43680
+
+signed short X[N] __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__)));
+signed int   Y[N] __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__)));
+
+/* (short, int)->int->int dot product.
+   Not detected as a dot-product pattern.  */
+
+__attribute__ ((noinline)) int
+foo (int len)
+{
+  int i;
+  int result = 0;
+
+  for (i = 0; i < len; i++)
+    {
+      result += (X[i] * Y[i]);
+    }
+  return result;
+}
+
+
+/* (int, short)->int->int dot product.
+   Not detected as a dot-product pattern.  */
+
+__attribute__ ((noinline)) int
+bar (int len)
+{
+  int i;
+  int result = 0;
+
+  for (i = 0; i < len; i++)
+    {
+      result += (Y[i] * X[i]);
+    }
+  return result;
+}
+
+int
+main (void)
+{
+  int i;
+  int dot;
+
+  check_vect ();
+
+  for (i = 0; i < N; i++)
+    {
+      X[i] = i;
+      Y[i] = N - i;
+      __asm__ volatile ("");
+    }
+
+  dot = foo (N);
+  if (dot != DOT)
+    abort ();
+
+  dot = bar (N);
+  if (dot != DOT)
+    abort ();
+
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" {
target vect_unpack } } } */
+/* { dg-final { cleanup-tree-dump "vect" } } */
+
Index: gcc/testsuite/ChangeLog
===================================================================
--- gcc/testsuite/ChangeLog (revision 202572)
+++ gcc/testsuite/ChangeLog (working copy)
@@ -1,3 +1,9 @@
+2013-09-13  Cong Hou  <congh@google.com>
+
+ * gcc.dg/vect/vect-reduc-dot-s16c.c: Add a test case with dot product
+ on two arrays with short and int types. This should not be recognized
+ as a dot product pattern.
+
 2013-09-13  Kai Tietz  <ktietz@redhat.com>

  gcc.target/i386/pr57848.c: New file.




On Wed, Sep 11, 2013 at 6:55 PM, Xinliang David Li <davidxl@google.com> wrote:
> Can you add a test case to the regression suite?
>
> When the type of arguments are unsigned short/unsigned int, GCC does
> not vectorize the loop anymore -- this is worth a separate bug to
> track. punpcklwd instruction can be used to do zero extension of the
> short type.
>
> David
>
> On Wed, Sep 11, 2013 at 6:16 PM, Cong Hou <congh@google.com> wrote:
>> Hi
>>
>> There is a bug in the function vect_recog_dot_prod_pattern() in
>> tree-vect-patterns.c. This function checks if a loop is of dot
>> production pattern. Specifically, according to the comment of this
>> function:
>>
>> /*
>>  Try to find the following pattern:
>>
>>      type x_t, y_t;
>>      TYPE1 prod;
>>      TYPE2 sum = init;
>>    loop:
>>      sum_0 = phi <init, sum_1>
>>      S1  x_t = ...
>>      S2  y_t = ...
>>      S3  x_T = (TYPE1) x_t;
>>      S4  y_T = (TYPE1) y_t;
>>      S5  prod = x_T * y_T;
>>      [S6  prod = (TYPE2) prod;  #optional]
>>      S7  sum_1 = prod + sum_0;
>>
>>    where 'TYPE1' is exactly double the size of type 'type', and
>> 'TYPE2' is the same size of 'TYPE1' or bigger. This is a special case
>> of a reduction computation.
>> */
>>
>> This function should check if x_t and y_t have the same type (type)
>> which has the half size of TYPE1. The corresponding code is shown
>> below:
>>
>>       oprnd0 = gimple_assign_rhs1 (stmt);
>>       oprnd1 = gimple_assign_rhs2 (stmt);
>>       if (!types_compatible_p (TREE_TYPE (oprnd0), prod_type) ||
>> !types_compatible_p (TREE_TYPE (oprnd1), prod_type))
>>         return NULL;
>>       if (!type_conversion_p (oprnd0, stmt, true, &half_type0,
>> &def_stmt, &promotion) || !promotion)
>>         return NULL;
>>       oprnd00 = gimple_assign_rhs1 (def_stmt);
>>
>> /*======================V  see here! */
>>       if (!type_conversion_p (oprnd0, stmt, true, &half_type1,
>> &def_stmt, &promotion) || !promotion)
>>         return NULL;
>>       oprnd01 = gimple_assign_rhs1 (def_stmt);
>>       if (!types_compatible_p (half_type0, half_type1))
>>         return NULL;
>>       if (TYPE_PRECISION (prod_type) != TYPE_PRECISION (half_type0) * 2)
>> return NULL;
>>
>> Here the function uses x_T (oprnd0) to check the type of y_t, which is
>> incorrect. The fix is simple: just replace it by oprnd1.
>>
>> The failed test case for this bug is shown below:
>>
>> int foo(short *a, int *b, int n) {
>>   int sum = 0;
>>   for (int i = 0; i < n; ++i)
>>     sum += a[i] * b[i];
>>   return sum;
>> }
>>
>>
>> thanks,
>> Cong
>>
>>
>> Index: gcc/tree-vect-patterns.c
>> ===================================================================
>> --- gcc/tree-vect-patterns.c (revision 200988)
>> +++ gcc/tree-vect-patterns.c (working copy)
>> @@ -397,7 +397,7 @@ vect_recog_dot_prod_pattern (vec<gimple>
>>            || !promotion)
>>          return NULL;
>>        oprnd00 = gimple_assign_rhs1 (def_stmt);
>> -      if (!type_conversion_p (oprnd0, stmt, true, &half_type1, &def_stmt,
>> +      if (!type_conversion_p (oprnd1, stmt, true, &half_type1, &def_stmt,
>>                                  &promotion)
>>            || !promotion)
>>          return NULL;


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