[PATCH 4/5] if-conv: Apply VN to hoisted conversions
Richard Sandiford
richard.sandiford@arm.com
Fri Nov 12 18:04:13 GMT 2021
This patch is a prerequisite for a later one. At the moment,
if-conversion converts predicated POINTER_PLUS_EXPRs into
non-wrapping forms, which for:
… = base + offset
becomes:
tmp = (unsigned long) base
… = tmp + offset
It then hoists these conversions out of the loop where possible.
However, because “base” is a valid gimple operand, there can be
multiple POINTER_PLUS_EXPRs with the same base, which can in turn
lead to multiple instances of the same conversion. The later VN pass
is (and I think needs to be) restricted to the new if-converted code,
whereas here we're deliberately inserting the conversions before the
.LOOP_VECTORIZED condition:
/* If we versioned loop then make sure to insert invariant
stmts before the .LOOP_VECTORIZED check since the vectorizer
will re-use that for things like runtime alias versioning
whose condition can end up using those invariants. */
We can therefore enter the vectoriser with redundant conversions.
The easiest fix seemed to be to defer the hoisting until after VN.
This catches other hoisting opportunities too.
Hoisting the code from the (artificial) loop in pr99102.c means
that it's no longer worth vectorising. The patch forces vectorisation
instead of relying on the cost model.
The patch also reverts pr87007-4.c and pr87007-5.c back to their
original forms, undoing changes in 783dc66f9ccb0019c3dad.
The code at the time the tests were added was:
testl %edi, %edi
je .L10
vxorps %xmm1, %xmm1, %xmm1
vsqrtsd d3(%rip), %xmm1, %xmm0
vsqrtsd d2(%rip), %xmm1, %xmm1
...
.L10:
ret
with the operations being hoisted, and the vxorps was specifically
wanted (compared to the previous code). This patch restores the code
to that form, with the hoisted operations and the vxorps.
Regstrapped on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Richard
gcc/
* tree-if-conv.c: Include tree-eh.h.
(predicate_statements): Remove pe argument. Don't hoist
statements here.
(combine_blocks): Remove pe argument.
(ifcvt_can_hoist, ifcvt_can_hoist_further): New functions.
(ifcvt_hoist_invariants): Likewise.
(tree_if_conversion): Update call to combine_blocks. Call
ifcvt_hoist_invariants after VN.
gcc/testsuite/
* gcc.dg/vect/pr99102.c: Add -fno-vect-cost-model.
Revert:
2020-09-09 Richard Biener <rguenther@suse.de>
* gcc.target/i386/pr87007-4.c: Adjust.
* gcc.target/i386/pr87007-5.c: Likewise.
---
gcc/testsuite/gcc.dg/vect/pr99102.c | 2 +-
gcc/testsuite/gcc.target/i386/pr87007-4.c | 2 +-
gcc/testsuite/gcc.target/i386/pr87007-5.c | 2 +-
gcc/tree-if-conv.c | 122 ++++++++++++++++++++--
4 files changed, 114 insertions(+), 14 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/vect/pr99102.c b/gcc/testsuite/gcc.dg/vect/pr99102.c
index 6c1a13f0783..0d030d15c86 100644
--- a/gcc/testsuite/gcc.dg/vect/pr99102.c
+++ b/gcc/testsuite/gcc.dg/vect/pr99102.c
@@ -1,4 +1,4 @@
-/* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-details" } */
+/* { dg-options "-O2 -ftree-vectorize -fno-vect-cost-model -fdump-tree-vect-details" } */
/* { dg-additional-options "-msve-vector-bits=256" { target aarch64_sve256_hw } } */
long a[44];
short d, e = -7;
diff --git a/gcc/testsuite/gcc.target/i386/pr87007-4.c b/gcc/testsuite/gcc.target/i386/pr87007-4.c
index 9c4b8005af3..e91bdcbac44 100644
--- a/gcc/testsuite/gcc.target/i386/pr87007-4.c
+++ b/gcc/testsuite/gcc.target/i386/pr87007-4.c
@@ -15,4 +15,4 @@ foo (int n, int k)
d1 = ceil (d3);
}
-/* { dg-final { scan-assembler-times "vxorps\[^\n\r\]*xmm\[0-9\]" 0 } } */
+/* { dg-final { scan-assembler-times "vxorps\[^\n\r\]*xmm\[0-9\]" 1 } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr87007-5.c b/gcc/testsuite/gcc.target/i386/pr87007-5.c
index e4d956a5d7f..20d13cf650b 100644
--- a/gcc/testsuite/gcc.target/i386/pr87007-5.c
+++ b/gcc/testsuite/gcc.target/i386/pr87007-5.c
@@ -15,4 +15,4 @@ foo (int n, int k)
d1 = sqrt (d3);
}
-/* { dg-final { scan-assembler-times "vxorps\[^\n\r\]*xmm\[0-9\]" 0 } } */
+/* { dg-final { scan-assembler-times "vxorps\[^\n\r\]*xmm\[0-9\]" 1 } } */
diff --git a/gcc/tree-if-conv.c b/gcc/tree-if-conv.c
index e88ddc9f788..0ad557a2f4d 100644
--- a/gcc/tree-if-conv.c
+++ b/gcc/tree-if-conv.c
@@ -121,6 +121,7 @@ along with GCC; see the file COPYING3. If not see
#include "tree-cfgcleanup.h"
#include "tree-ssa-dse.h"
#include "tree-vectorizer.h"
+#include "tree-eh.h"
/* Only handle PHIs with no more arguments unless we are asked to by
simd pragma. */
@@ -2496,7 +2497,7 @@ predicate_rhs_code (gassign *stmt, tree mask, tree cond,
*/
static void
-predicate_statements (loop_p loop, edge pe)
+predicate_statements (loop_p loop)
{
unsigned int i, orig_loop_num_nodes = loop->num_nodes;
auto_vec<int, 1> vect_sizes;
@@ -2597,13 +2598,7 @@ predicate_statements (loop_p loop, edge pe)
{
gassign *stmt2 = as_a <gassign *> (gsi_stmt (gsi2));
gsi_remove (&gsi2, false);
- /* Make sure to move invariant conversions out of the
- loop. */
- if (CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (stmt2))
- && expr_invariant_in_loop_p (loop,
- gimple_assign_rhs1 (stmt2)))
- gsi_insert_on_edge_immediate (pe, stmt2);
- else if (first)
+ if (first)
{
gsi_insert_before (&gsi, stmt2, GSI_NEW_STMT);
first = false;
@@ -2684,7 +2679,7 @@ remove_conditions_and_labels (loop_p loop)
blocks. Replace PHI nodes with conditional modify expressions. */
static void
-combine_blocks (class loop *loop, edge pe)
+combine_blocks (class loop *loop)
{
basic_block bb, exit_bb, merge_target_bb;
unsigned int orig_loop_num_nodes = loop->num_nodes;
@@ -2697,7 +2692,7 @@ combine_blocks (class loop *loop, edge pe)
predicate_all_scalar_phis (loop);
if (need_to_predicate || need_to_rewrite_undefined)
- predicate_statements (loop, pe);
+ predicate_statements (loop);
/* Merge basic blocks. */
exit_bb = NULL;
@@ -3181,6 +3176,109 @@ ifcvt_local_dce (class loop *loop)
}
}
+/* Return true if STMT can be hoisted from if-converted loop LOOP. */
+
+static bool
+ifcvt_can_hoist (class loop *loop, gimple *stmt)
+{
+ if (auto *call = dyn_cast<gcall *> (stmt))
+ {
+ if (gimple_call_internal_p (call)
+ && internal_fn_mask_index (gimple_call_internal_fn (call)) >= 0)
+ return false;
+ }
+ else if (auto *assign = dyn_cast<gassign *> (stmt))
+ {
+ if (gimple_assign_rhs_code (assign) == COND_EXPR)
+ return false;
+ }
+ else
+ return false;
+
+ if (gimple_has_side_effects (stmt)
+ || gimple_could_trap_p (stmt)
+ || stmt_could_throw_p (cfun, stmt)
+ || gimple_vdef (stmt)
+ || gimple_vuse (stmt))
+ return false;
+
+ int num_args = gimple_num_args (stmt);
+ for (int i = 0; i < num_args; ++i)
+ if (!expr_invariant_in_loop_p (loop, gimple_arg (stmt, i)))
+ return false;
+
+ return true;
+}
+
+/* PE is the preferred hoisting edge selected by tree_if_conversion, which
+ s known to be different from (and to dominate) the preheader edge of the
+ if-converted loop. We already know that STMT can be inserted on the loop
+ preheader edge. Return true if we prefer to insert it on PE instead. */
+
+static bool
+ifcvt_can_hoist_further (edge pe, gimple *stmt)
+{
+ /* As explained in tree_if_conversion, we want to hoist invariant
+ conversions further so that they can be reused by alias analysis. */
+ auto *assign = dyn_cast<gassign *> (stmt);
+ if (assign
+ && CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (assign)))
+ {
+ tree rhs = gimple_assign_rhs1 (assign);
+ if (is_gimple_min_invariant (rhs))
+ return true;
+
+ if (TREE_CODE (rhs) == SSA_NAME)
+ {
+ basic_block def_bb = gimple_bb (SSA_NAME_DEF_STMT (rhs));
+ if (!def_bb || dominated_by_p (CDI_DOMINATORS, pe->dest, def_bb))
+ return true;
+ }
+ }
+ return false;
+}
+
+/* Hoist invariant statements from LOOP. PE is the preferred edge for
+ hoisting conversions, as selected by tree_if_conversion; see there
+ for details. */
+
+static void
+ifcvt_hoist_invariants (class loop *loop, edge pe)
+{
+ gimple_stmt_iterator hoist_gsi = {};
+ gimple_stmt_iterator hoist_gsi_pe = {};
+ unsigned int num_blocks = loop->num_nodes;
+ basic_block *body = get_loop_body (loop);
+ for (unsigned int i = 0; i < num_blocks; ++i)
+ for (gimple_stmt_iterator gsi = gsi_start_bb (body[i]); !gsi_end_p (gsi);)
+ {
+ gimple *stmt = gsi_stmt (gsi);
+ if (ifcvt_can_hoist (loop, stmt))
+ {
+ /* Once we've hoisted one statement, insert other statements
+ after it. */
+ edge e = loop_preheader_edge (loop);
+ gimple_stmt_iterator *hoist_gsi_ptr = &hoist_gsi;
+ if (e != pe && ifcvt_can_hoist_further (pe, stmt))
+ {
+ e = pe;
+ hoist_gsi_ptr = &hoist_gsi_pe;
+ }
+ gsi_remove (&gsi, false);
+ if (hoist_gsi_ptr->ptr)
+ gsi_insert_after (hoist_gsi_ptr, stmt, GSI_NEW_STMT);
+ else
+ {
+ gsi_insert_on_edge_immediate (e, stmt);
+ *hoist_gsi_ptr = gsi_for_stmt (stmt);
+ }
+ continue;
+ }
+ gsi_next (&gsi);
+ }
+ free (body);
+}
+
/* If-convert LOOP when it is legal. For the moment this pass has no
profitability analysis. Returns non-zero todo flags when something
changed. */
@@ -3275,7 +3373,7 @@ tree_if_conversion (class loop *loop, vec<gimple *> *preds)
/* Now all statements are if-convertible. Combine all the basic
blocks into one huge basic block doing the if-conversion
on-the-fly. */
- combine_blocks (loop, pe);
+ combine_blocks (loop);
/* Perform local CSE, this esp. helps the vectorizer analysis if loads
and stores are involved. CSE only the loop body, not the entry
@@ -3297,6 +3395,8 @@ tree_if_conversion (class loop *loop, vec<gimple *> *preds)
ifcvt_local_dce (loop);
BITMAP_FREE (exit_bbs);
+ ifcvt_hoist_invariants (loop, pe);
+
todo |= TODO_cleanup_cfg;
cleanup:
--
2.25.1
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