Hi,
This is a followup patch better handling below case:
for (i = 0; i < n; i++)
{
a[i] = 1;
a[i+2] = 2;
}
Instead of generating root variables by loading from memory and propagating
with PHI
nodes, like:
t0 = a[0];
t1 = a[1];
for (i = 0; i < n; i++)
{
a[i] = 1;
t2 = 2;
t0 = t1;
t1 = t2;
}
a[n] = t0;
a[n+1] = t1;
We can simply store loop invariant values after loop body if we know loop
iterates more
than chain->length times, like:
for (i = 0; i < n; i++)
{
a[i] = 1;
}
a[n] = 2;
a[n+1] = 2;
Bootstrap(O2/O3) in patch series on x86_64 and AArch64. Is it OK?
Thanks,
bin
2017-06-21 Bin Cheng <bin.ch...@arm.com>
* tree-predcom.c: (struct chain): Handle store-store chain in which
stores for elimination only store loop invariant values.
(execute_pred_commoning_chain): Ditto.
(prepare_initializers_chain_store_elim): Ditto.
(prepare_finalizers): Ditto.
(is_inv_store_elimination_chain): New function.
(initialize_root_vars_store_elim_1): New function.From 16603c31d42e44f93a5de0faa0354629e669c5d0 Mon Sep 17 00:00:00 2001
From: Bin Cheng <binch...@e108451-lin.cambridge.arm.com>
Date: Wed, 21 Jun 2017 16:18:43 +0100
Subject: [PATCH 6/6] inv-store-elimination-20170621.txt
---
gcc/tree-predcom.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 125 insertions(+), 6 deletions(-)
diff --git a/gcc/tree-predcom.c b/gcc/tree-predcom.c
index 9be93e4..8e38be4 100644
--- a/gcc/tree-predcom.c
+++ b/gcc/tree-predcom.c
@@ -327,6 +327,10 @@ typedef struct chain
/* True if this chain was combined together with some other chain. */
unsigned combined : 1;
+
+ /* True if this is store elimination chain and eliminated stores store
+ loop invariant value into memory. */
+ unsigned inv_store_elimination : 1;
} *chain_p;
@@ -1630,6 +1634,98 @@ initialize_root_vars (struct loop *loop, chain_p chain,
bitmap tmp_vars)
}
}
+/* For inter-iteration store elimination CHAIN in LOOP, returns true if
+ all stores to be eliminated store loop invariant values into memory.
+ In this case, we can use these invariant values directly after LOOP. */
+
+static bool
+is_inv_store_elimination_chain (struct loop *loop, chain_p chain)
+{
+ if (chain->length == 0 || chain->type != CT_STORE_STORE)
+ return false;
+
+ gcc_assert (!chain->has_max_use_after);
+
+ /* If loop iterates for unknown times or fewer times than chain->lenght,
+ we still need to setup root variable and propagate it with PHI node. */
+ tree niters = number_of_latch_executions (loop);
+ if (TREE_CODE (niters) != INTEGER_CST || wi::leu_p (niters, chain->length))
+ return false;
+
+ /* Check stores in chain for elimination if they only store loop invariant
+ values. */
+ for (unsigned i = 0; i < chain->length; i++)
+ {
+ dref a = get_chain_last_ref_at (chain, i);
+ if (a == NULL)
+ continue;
+
+ gimple *def_stmt, *stmt = a->stmt;
+ if (!gimple_assign_single_p (stmt))
+ return false;
+
+ tree val = gimple_assign_rhs1 (stmt);
+ if (TREE_CLOBBER_P (val))
+ return false;
+
+ if (TREE_CODE (val) == INTEGER_CST || TREE_CODE (val) == REAL_CST)
+ continue;
+
+ if (TREE_CODE (val) != SSA_NAME)
+ return false;
+
+ def_stmt = SSA_NAME_DEF_STMT (val);
+ if (gimple_nop_p (def_stmt))
+ continue;
+
+ if (flow_bb_inside_loop_p (loop, gimple_bb (def_stmt)))
+ return false;
+ }
+ return true;
+}
+
+/* Creates root variables for store elimination CHAIN in which stores for
+ elimination only store loop invariant values. In this case, we neither
+ need to load root variables before loop nor propagate it with PHI nodes. */
+
+static void
+initialize_root_vars_store_elim_1 (chain_p chain)
+{
+ tree var;
+ unsigned i, n = chain->length;
+
+ chain->vars.create (n);
+ chain->vars.safe_grow_cleared (n);
+
+ /* Initialize root value for eliminated stores at each distance. */
+ for (i = 0; i < n; i++)
+ {
+ dref a = get_chain_last_ref_at (chain, i);
+ if (a == NULL)
+ continue;
+
+ var = gimple_assign_rhs1 (a->stmt);
+ chain->vars[a->distance] = var;
+ }
+
+ /* We don't propagate values with PHI nodes, so manually propagate value
+ to bubble positions. */
+ var = chain->vars[0];
+ for (i = 1; i < n; i++)
+ {
+ if (chain->vars[i] != NULL_TREE)
+ {
+ var = chain->vars[i];
+ continue;
+ }
+ chain->vars[i] = var;
+ }
+
+ /* Revert the vector. */
+ for (i = 0; i < n / 2; i++)
+ std::swap (chain->vars[i], chain->vars[n - i - 1]);
+}
+
/* Creates root variables for store elimination CHAIN in which stores for
elimination store loop variant values. In this case, we may need to
load root variables before LOOP and propagate it with PHI nodes. Uids
@@ -1953,10 +2049,20 @@ execute_pred_commoning_chain (struct loop *loop,
chain_p chain,
{
if (chain->length > 0)
{
- /* For inter-iteration store elimination chain, set up the
- variables by loading from memory before loop, copying from rhs
- of stores for elimination and propagate it with PHI nodes. */
- initialize_root_vars_store_elim_2 (loop, chain, tmp_vars);
+ if (chain->inv_store_elimination)
+ {
+ /* If dead stores in this chain only store loop invariant
+ values, we can simply record the invariant value and use
+ it directly after loop. */
+ initialize_root_vars_store_elim_1 (chain);
+ }
+ else
+ {
+ /* If dead stores in this chain store loop variant values,
+ we need to set up the variables by loading from memory
+ before loop and propagating it with PHI nodes. */
+ initialize_root_vars_store_elim_2 (loop, chain, tmp_vars);
+ }
/* For inter-iteration store elimination chain, stores at each
distance in loop's last (chain->length - 1) iterations can't
@@ -2657,7 +2763,7 @@ try_combine_chains (vec<chain_p> *chains)
otherwise. */
static bool
-prepare_initializers_chain_store_elim (struct loop *, chain_p chain)
+prepare_initializers_chain_store_elim (struct loop *loop, chain_p chain)
{
unsigned i, n = chain->length;
@@ -2665,6 +2771,15 @@ prepare_initializers_chain_store_elim (struct loop *,
chain_p chain)
if (n == 0 && chain->type == CT_STORE_STORE)
return true;
+ /* For store elimination chain, there is nothing to initialize if stores
+ to be eliminated only store loop invariant values into memory. */
+ if (chain->type == CT_STORE_STORE
+ && is_inv_store_elimination_chain (loop, chain))
+ {
+ chain->inv_store_elimination = true;
+ return true;
+ }
+
chain->inits.create (n);
chain->inits.safe_grow_cleared (n);
@@ -2864,7 +2979,11 @@ prepare_finalizers (struct loop *loop, vec<chain_p>
chains)
if (prepare_finalizers_chain (loop, chain))
{
i++;
- loop_closed_ssa = true;
+ /* We don't corrupt loop closed ssa form for store elimination
+ chain if eliminated stores only store loop invariant values
+ into memory. */
+ if (!chain->inv_store_elimination)
+ loop_closed_ssa |= (!chain->inv_store_elimination);
}
else
{
--
1.9.1
