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bswap: Fix up recent vector CONSTRUCTOR optimization [PR98568] 

As the testcase shows, bswap can match even byte-swapping or indentity
from low part of some wider SSA_NAME.
For bswap replacement other than for vector CONSTRUCTOR the code has been
using NOP_EXPR casts if the types weren't compatible, but for vectors
we need to use VIEW_CONVERT_EXPR.  The problem with the latter is that
we require that it has the same size, which isn't guaranteed, so this patch
in those cases first adds a narrowing NOP_EXPR cast and only afterwards
does a VIEW_CONVERT_EXPR.

2021-01-07  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/98568
	* gimple-ssa-store-merging.c (bswap_view_convert): New function.
	(bswap_replace): Use it.

	* g++.dg/torture/pr98568.C: New test.
This commit is contained in:
Jakub Jelinek 2021-01-07 09:57:40 +01:00
parent 1b56697524
commit d02a8b63e5
2 changed files with 59 additions and 3 deletions
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25
gcc/gimple-ssa-store-merging.c
View File

@ -978,6 +978,25 @@ public:
}; // class pass_optimize_bswap
/* Helper function for bswap_replace. Build VIEW_CONVERT_EXPR from
VAL to TYPE. If VAL has different type size, emit a NOP_EXPR cast
first. */
static tree
bswap_view_convert (gimple_stmt_iterator *gsi, tree type, tree val)
{
gcc_assert (INTEGRAL_TYPE_P (TREE_TYPE (val)));
if (TYPE_SIZE (type) != TYPE_SIZE (TREE_TYPE (val)))
{
HOST_WIDE_INT prec = TREE_INT_CST_LOW (TYPE_SIZE (type));
tree itype = build_nonstandard_integer_type (prec, 1);
gimple *g = gimple_build_assign (make_ssa_name (itype), NOP_EXPR, val);
gsi_insert_before (gsi, g, GSI_SAME_STMT);
val = gimple_assign_lhs (g);
}
return build1 (VIEW_CONVERT_EXPR, type, val);
}
/* Perform the bswap optimization: replace the expression computed in the rhs
of gsi_stmt (GSI) (or if NULL add instead of replace) by an equivalent
bswap, load or load + bswap expression.
@ -1100,7 +1119,7 @@ bswap_replace (gimple_stmt_iterator gsi, gimple *ins_stmt, tree fndecl,
gimple_set_vuse (load_stmt, n->vuse);
gsi_insert_before (&gsi, load_stmt, GSI_SAME_STMT);
if (conv_code == VIEW_CONVERT_EXPR)
val_tmp = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (tgt), val_tmp);
val_tmp = bswap_view_convert (&gsi, TREE_TYPE (tgt), val_tmp);
gimple_assign_set_rhs_with_ops (&gsi, conv_code, val_tmp);
update_stmt (cur_stmt);
}
@ -1144,7 +1163,7 @@ bswap_replace (gimple_stmt_iterator gsi, gimple *ins_stmt, tree fndecl,
if (!is_gimple_val (src))
return NULL_TREE;
if (conv_code == VIEW_CONVERT_EXPR)
src = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (tgt), src);
src = bswap_view_convert (&gsi, TREE_TYPE (tgt), src);
g = gimple_build_assign (tgt, conv_code, src);
}
else if (cur_stmt)
@ -1227,7 +1246,7 @@ bswap_replace (gimple_stmt_iterator gsi, gimple *ins_stmt, tree fndecl,
tmp = make_temp_ssa_name (bswap_type, NULL, "bswapdst");
tree atmp = tmp;
if (conv_code == VIEW_CONVERT_EXPR)
atmp = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (tgt), tmp);
atmp = bswap_view_convert (&gsi, TREE_TYPE (tgt), tmp);
convert_stmt = gimple_build_assign (tgt, conv_code, atmp);
gsi_insert_after (&gsi, convert_stmt, GSI_SAME_STMT);
}

37
gcc/testsuite/g++.dg/torture/pr98568.C Normal file
View File

@ -0,0 +1,37 @@
// PR tree-optimization/98568
// { dg-do compile }
char a[2];
char b[4];
void
foo (int x)
{
a[1] = x >> 8;
a[0] = x;
}
void
bar (long long x)
{
b[3] = x >> 24;
b[2] = x >> 16;
b[1] = x >> 8;
b[0] = x;
}
void
baz (int x)
{
a[0] = x >> 8;
a[1] = x;
}
void
qux (long long x)
{
b[0] = x >> 24;
b[1] = x >> 16;
b[2] = x >> 8;
b[3] = x;
}