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middle-end/105715 - missed RTL if-conversion with COND_EXPR expansion

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When the COND_EXPR condition operand was split out to a separate stmt
it became subject to CSE with other condition evaluations.  This
unfortunately leads to TER no longer applying and in turn RTL
expansion of COND_EXPRs no longer seeing the condition and thus
failing to try conditional move expansion.  This can be seen with
gcc.target/i386/pr45685.c when built with -march=cascadelake which
then FAILs to produce the expected number of cmovs.

It can also be seen when we create more COND_EXPRs early like for
instruction selection of MIN/MAX operations that map to IEEE
a > b ? a : b expression semantics.

	PR middle-end/105715
	* gimple-isel.cc (gimple_expand_vec_exprs): Merge into...
	(pass_gimple_isel::execute): ... this.  Duplicate
	comparison defs of COND_EXPRs.
This commit is contained in:
Richard Biener 2023-07-18 10:02:52 +02:00
parent cde17323f9
commit cbe5f6859a
1 changed files with 83 additions and 44 deletions
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127
gcc/gimple-isel.cc
View file

@ -336,47 +336,6 @@ gimple_expand_vec_cond_expr (struct function *fun, gimple_stmt_iterator *gsi,
/* Iterate all gimple statements and try to expand
VEC_COND_EXPR assignments. */
static unsigned int
gimple_expand_vec_exprs (struct function *fun)
{
gimple_stmt_iterator gsi;
basic_block bb;
hash_map<tree, unsigned int> vec_cond_ssa_name_uses;
auto_bitmap dce_ssa_names;
bool cfg_changed = false;
FOR_EACH_BB_FN (bb, fun)
{
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple *g = gimple_expand_vec_cond_expr (fun, &gsi,
&vec_cond_ssa_name_uses);
if (g != NULL)
{
tree lhs = gimple_assign_lhs (gsi_stmt (gsi));
gimple_set_lhs (g, lhs);
gsi_replace (&gsi, g, false);
}
cfg_changed |= gimple_expand_vec_set_extract_expr (fun, &gsi);
if (gsi_end_p (gsi))
break;
}
}
for (hash_map<tree, unsigned int>::iterator it = vec_cond_ssa_name_uses.begin ();
it != vec_cond_ssa_name_uses.end (); ++it)
bitmap_set_bit (dce_ssa_names, SSA_NAME_VERSION ((*it).first));
simple_dce_from_worklist (dce_ssa_names);
return cfg_changed ? TODO_cleanup_cfg : 0;
}
namespace {
const pass_data pass_data_gimple_isel =
@ -405,12 +364,92 @@ public:
return true;
}
unsigned int execute (function *fun) final override
unsigned int execute (function *fun) final override;
}; // class pass_gimple_isel
/* Iterate all gimple statements and perform pre RTL expansion
GIMPLE massaging to improve instruction selection. */
unsigned int
pass_gimple_isel::execute (struct function *fun)
{
gimple_stmt_iterator gsi;
basic_block bb;
hash_map<tree, unsigned int> vec_cond_ssa_name_uses;
auto_bitmap dce_ssa_names;
bool cfg_changed = false;
FOR_EACH_BB_FN (bb, fun)
{
return gimple_expand_vec_exprs (fun);
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
/* Pre-expand VEC_COND_EXPRs to .VCOND* internal function
calls mapping to supported optabs. */
gimple *g = gimple_expand_vec_cond_expr (fun, &gsi,
&vec_cond_ssa_name_uses);
if (g != NULL)
{
tree lhs = gimple_assign_lhs (gsi_stmt (gsi));
gimple_set_lhs (g, lhs);
gsi_replace (&gsi, g, false);
}
/* Recognize .VEC_SET and .VEC_EXTRACT patterns. */
cfg_changed |= gimple_expand_vec_set_extract_expr (fun, &gsi);
if (gsi_end_p (gsi))
break;
gassign *stmt = dyn_cast <gassign *> (*gsi);
if (!stmt)
continue;
tree_code code = gimple_assign_rhs_code (stmt);
tree lhs = gimple_assign_lhs (stmt);
if (TREE_CODE_CLASS (code) == tcc_comparison
&& !has_single_use (lhs))
{
/* Duplicate COND_EXPR condition defs when they are
comparisons so RTL expansion with the help of TER
can perform better if conversion. */
imm_use_iterator imm_iter;
use_operand_p use_p;
auto_vec<gassign *, 4> cond_exprs;
unsigned cnt = 0;
FOR_EACH_IMM_USE_FAST (use_p, imm_iter, lhs)
{
if (is_gimple_debug (USE_STMT (use_p)))
continue;
cnt++;
if (gimple_bb (USE_STMT (use_p)) == bb
&& is_gimple_assign (USE_STMT (use_p))
&& gimple_assign_rhs1_ptr (USE_STMT (use_p)) == use_p->use
&& gimple_assign_rhs_code (USE_STMT (use_p)) == COND_EXPR)
cond_exprs.safe_push (as_a <gassign *> (USE_STMT (use_p)));
}
for (unsigned i = cond_exprs.length () == cnt ? 1 : 0;
i < cond_exprs.length (); ++i)
{
gassign *copy = as_a <gassign *> (gimple_copy (stmt));
tree new_def = duplicate_ssa_name (lhs, copy);
gimple_assign_set_lhs (copy, new_def);
auto gsi2 = gsi_for_stmt (cond_exprs[i]);
gsi_insert_before (&gsi2, copy, GSI_SAME_STMT);
gimple_assign_set_rhs1 (cond_exprs[i], new_def);
update_stmt (cond_exprs[i]);
}
}
}
}
}; // class pass_gimple_isel
for (auto it = vec_cond_ssa_name_uses.begin ();
it != vec_cond_ssa_name_uses.end (); ++it)
bitmap_set_bit (dce_ssa_names, SSA_NAME_VERSION ((*it).first));
simple_dce_from_worklist (dce_ssa_names);
return cfg_changed ? TODO_cleanup_cfg : 0;
}
} // anon namespace