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[GCC, Vect] Fix costing for vector shifts

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While looking at the vectorization for following example, we realized that
even though vectorizable_shift function was distinguishing vector shifted
by vector from vector shifted by scalar, while modelling the cost it would
always add the cost of building a vector constant despite not needing it for
vector shifted by scalar.

This patch fixes this by using scalar_shift_arg to determine whether we need
to build a vector for the second operand or not. This causes the test case
below to now vectorize.

gcc/ChangeLog:

2019-12-09  Sudakshina Das  <sudi.das@arm.com>
	    Richard Sandiford  <richard.sandiford@arm.com>

	* tree-vect-stmt.c (vectorizable_shift): Condition ndts for
	vect_model_simple_cost call on scalar_shift_arg.

gcc/testsuite/ChangeLog:

2019-12-09  Sudakshina Das  <sudi.das@arm.com>

	* gcc.dg/vect/vect-shift-5.c: New test.

Co-Authored-By: Richard Sandiford <richard.sandiford@arm.com>

From-SVN: r279114
This commit is contained in:
Sudakshina Das 2019-12-09 10:22:01 +00:00 committed by Sudakshina Das
parent 49647b7b25
commit e3126e5f64
4 changed files with 31 additions and 1 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2019-12-09 Sudakshina Das <sudi.das@arm.com>
Richard Sandiford <richard.sandiford@arm.com>
* tree-vect-stmt.c (vectorizable_shift): Condition ndts for
vect_model_simple_cost call on scalar_shift_arg.
2019-12-09 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/92834

4
gcc/testsuite/ChangeLog
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@ -1,3 +1,7 @@
2019-12-09 Sudakshina Das <sudi.das@arm.com>
* gcc.dg/vect/vect-shift-5.c: New test.
2019-12-09 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/92834

19
gcc/testsuite/gcc.dg/vect/vect-shift-5.c Normal file
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@ -0,0 +1,19 @@
/* { dg-do compile } */
/* { dg-require-effective-target vect_shift } */
/* { dg-require-effective-target vect_int } */
typedef unsigned int uint32_t;
typedef short unsigned int uint16_t;
int foo (uint32_t arr[4][4])
{
int sum = 0;
for(int i = 0; i < 4; i++)
{
sum += ((arr[0][i] >> 10) * 20) + ((arr[1][i] >> 11) & 53)
+ ((arr[2][i] >> 12) * 7) + ((arr[3][i] >> 13) ^ 43);
}
return (((uint16_t)sum) + ((uint32_t)sum >> 16)) >> 1;
}
/* { dg-final { scan-tree-dump {vectorizable_shift ===[\n\r][^\n]*prologue_cost = 0} "vect" } } */

3
gcc/tree-vect-stmts.c
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@ -5764,7 +5764,8 @@ vectorizable_shift (stmt_vec_info stmt_info, gimple_stmt_iterator *gsi,
{
STMT_VINFO_TYPE (stmt_info) = shift_vec_info_type;
DUMP_VECT_SCOPE ("vectorizable_shift");
vect_model_simple_cost (stmt_info, ncopies, dt, ndts, slp_node, cost_vec);
vect_model_simple_cost (stmt_info, ncopies, dt,
scalar_shift_arg ? 1 : ndts, slp_node, cost_vec);
return true;
}