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improve VN PHI hashing 

This reduces the number of collisions for PHIs in the VN hashtable
by always hashing the number of predecessors and separately hashing
the block number when we never merge PHIs from different blocks.

This improves collisions seen for the PR69609 testcase dramatically.

2020-11-13  Richard Biener  <rguenther@suse.de>

	* tree-ssa-sccvn.c (vn_phi_compute_hash): Always hash the
	number of predecessors.  Hash the block number also for
	loop header PHIs.
	(expressions_equal_p): Short-cut SSA name compares, remove
	test for NULL operands.
	(vn_phi_eq): Cache number of predecessors, change inlined
	test from expressions_equal_p.
This commit is contained in:
Richard Biener 2020-11-13 13:17:01 +01:00
parent be6169045e
commit 4d6b8d4213
1 changed files with 21 additions and 6 deletions
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27
gcc/tree-ssa-sccvn.c
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@ -4126,13 +4126,27 @@ vn_nary_op_insert_stmt (gimple *stmt, tree result)
static inline hashval_t
vn_phi_compute_hash (vn_phi_t vp1)
{
inchash::hash hstate (EDGE_COUNT (vp1->block->preds) > 2
? vp1->block->index : EDGE_COUNT (vp1->block->preds));
inchash::hash hstate;
tree phi1op;
tree type;
edge e;
edge_iterator ei;
hstate.add_int (EDGE_COUNT (vp1->block->preds));
switch (EDGE_COUNT (vp1->block->preds))
{
case 1:
break;
case 2:
if (vp1->block->loop_father->header == vp1->block)
;
else
break;
/* Fallthru. */
default:
hstate.add_int (vp1->block->index);
}
/* If all PHI arguments are constants we need to distinguish
the PHI node via its type. */
type = vp1->type;
@ -4277,11 +4291,12 @@ vn_phi_eq (const_vn_phi_t const vp1, const_vn_phi_t const vp2)
/* Any phi in the same block will have it's arguments in the
same edge order, because of how we store phi nodes. */
for (unsigned i = 0; i < EDGE_COUNT (vp1->block->preds); ++i)
unsigned nargs = EDGE_COUNT (vp1->block->preds);
for (unsigned i = 0; i < nargs; ++i)
{
tree phi1op = vp1->phiargs[i];
tree phi2op = vp2->phiargs[i];
if (phi1op == VN_TOP || phi2op == VN_TOP)
if (phi1op == phi2op)
continue;
if (!expressions_equal_p (phi1op, phi2op))
return false;
@ -5612,8 +5627,8 @@ expressions_equal_p (tree e1, tree e2)
if (e1 == VN_TOP || e2 == VN_TOP)
return true;
/* If only one of them is null, they cannot be equal. */
if (!e1 || !e2)
/* SSA_NAME compare pointer equal. */
if (TREE_CODE (e1) == SSA_NAME || TREE_CODE (e2) == SSA_NAME)
return false;
/* Now perform the actual comparison. */