On 6/30/20 12:38 PM, Richard Biener wrote:
On Tue, Jun 30, 2020 at 11:44 AM Martin Liška <mli...@suse.cz> wrote:
Hi.
The patch is about blocking of vector expansion of comparisons
that are only feeding a VEC_COND_EXPR statements.
Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
The problematic mips64 test-case looks good now.
Ready to be installed?
So why does
static tree
expand_vector_comparison (gimple_stmt_iterator *gsi, tree type, tree op0,
tree op1, enum tree_code code)
{
tree t;
if (!expand_vec_cmp_expr_p (TREE_TYPE (op0), type, code)
&& !expand_vec_cond_expr_p (type, TREE_TYPE (op0), code))
^^^^
not return true
Apparently because it's called for type:
(gdb) p debug_tree(gimple_expr_type(stmt))
<vector_type 0x7ffff7721348
type <boolean_type 0x7ffff77212a0 SI
size <integer_cst 0x7ffff76338e8 constant 32>
unit-size <integer_cst 0x7ffff7633900 constant 4>
align:32 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type 0x7ffff77212a0
precision:32 min <integer_cst 0x7ffff773e750 -2147483648> max <integer_cst
0x7ffff773e768 2147483647>>
BLK
size <integer_cst 0x7ffff76336a8 type <integer_type 0x7ffff76370a8
bitsizetype> constant 64>
unit-size <integer_cst 0x7ffff76336c0 type <integer_type 0x7ffff7637000
sizetype> constant 8>
align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7ffff7721348 nunits:2>
while ...
{
but
/* Expand a vector condition to scalars, by using many conditions
on the vector's elements. */
static void
expand_vector_condition (gimple_stmt_iterator *gsi, auto_bitmap *dce_ssa_names)
{
...
if (expand_vec_cond_expr_p (type, TREE_TYPE (a1), code))
{
gcc_assert (TREE_CODE (a) == SSA_NAME || TREE_CODE (a) == VECTOR_CST);
return;
does?
this has
<vector_type 0x7ffff76fb3f0
type <real_type 0x7ffff763e2a0 float SF
size <integer_cst 0x7ffff76338e8 constant 32>
unit-size <integer_cst 0x7ffff7633900 constant 4>
align:32 warn_if_not_align:0 symtab:0 alias-set 1 canonical-type
0x7ffff763e2a0 precision:32
pointer_to_this <pointer_type 0x7ffff763e7e0>>
V2SF
size <integer_cst 0x7ffff76336a8 type <integer_type 0x7ffff76370a8
bitsizetype> constant 64>
unit-size <integer_cst 0x7ffff76336c0 type <integer_type 0x7ffff7637000
sizetype> constant 8>
align:64 warn_if_not_align:0 symtab:0 alias-set 1 canonical-type
0x7ffff76fb3f0 nunits:2
pointer_to_this <pointer_type 0x7ffff7721000>>
What's special about the problematical mips testcase?
That we end up with something like:
_34 = {_29, _37};
vect_iftmp.12_35 = VEC_COND_EXPR <_34, vect__1.7_28, vect__2.10_31>;
which can't be expanded to .VCOND, but we expand to series of BIT_FIELD_REFs:
_40 = BIT_FIELD_REF <vect__2.10_31, 32, 0>;
_22 = BIT_FIELD_REF <_34, 32, 0>;
_10 = _22 != 0 ? _26 : _40;
_16 = BIT_FIELD_REF <vect__2.10_31, 32, 32>;
_18 = BIT_FIELD_REF <_34, 32, 32>;
_41 = _18 == 0 ? _16 : _30;
Can't you produce
the same "bad" result when the comparison is used in a non-VEC_COND?
Theoretically yes.
Anyway, question is how much do we care about the fallout as it happens for
MIPS and
it's only a worse code stuff?
Martin
There's a PR reference missing in the ChangeLog.
Richard.
Thanks,
Martin
gcc/ChangeLog:
* tree-vect-generic.c (expand_vector_comparison): Do not expand
comparison that only feed first argument of a VEC_COND_EXPR statement.
---
gcc/tree-vect-generic.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/gcc/tree-vect-generic.c b/gcc/tree-vect-generic.c
index a4b56195903..4606decd0f2 100644
--- a/gcc/tree-vect-generic.c
+++ b/gcc/tree-vect-generic.c
@@ -379,6 +379,30 @@ static tree
expand_vector_comparison (gimple_stmt_iterator *gsi, tree type, tree op0,
tree op1, enum tree_code code)
{
+ tree lhs = gimple_assign_lhs (gsi_stmt (*gsi));
+ use_operand_p use_p;
+ imm_use_iterator iterator;
+ bool vec_cond_expr_only = true;
+ bool has_use = false;
+
+ /* As seen in PR95830, we should not expand comparisons that are only
+ feeding a VEC_COND_EXPR statement. */
+ FOR_EACH_IMM_USE_FAST (use_p, iterator, lhs)
+ {
+ has_use = true;
+ gassign *use = dyn_cast<gassign *> (USE_STMT (use_p));
+ if (use == NULL
+ || gimple_assign_rhs_code (use) != VEC_COND_EXPR
+ || gimple_assign_rhs1 (use) != lhs)
+ {
+ vec_cond_expr_only = false;
+ break;
+ }
+ }
+
+ if (has_use && vec_cond_expr_only)
+ return NULL_TREE;
+
tree t;
if (!expand_vec_cmp_expr_p (TREE_TYPE (op0), type, code)
&& !expand_vec_cond_expr_p (type, TREE_TYPE (op0), code))
--
2.27.0
