On Fri, Dec 16, 2016 at 02:16:40PM +0100, Richard Biener wrote:
> > Is memset and = {} equivalent even for aggregates with paddings?
>
> When lowering memset to = {} you should use
>
> MEM<char[]> (&decl, off-of-original-alias-type) = {}-of-type-char[];
>
> similar for lowering of memcpy (I think what gimple-fold.c does
> for example is slightly unsafe). But in practice I think nothing
> in GCC assumes you can lower accesses and ignore padding if that
> pass (like SRA) does not see all accesses to prove that is safe.
>
> > If val is not zero, then I can only handle it if stmt is memcpy,
> > (or in theory if stmt is assignment, and dest is addressable it
> > could be transformed into memset). If val is zero, and dest isn't
> > volatile and the size matches the size of dest, then perhaps it
> > could be transformed into = {} (if there are no paddings/bitfields
> > or if it doesn't matter), I haven't done that for simplicity indeed.
>
> Yes, please add a comment so a curious bystander doesn't have to figure
> that out himself.
So like this (if it passes bootstrap/regtest)?
2016-12-16 Jakub Jelinek <ja...@redhat.com>
PR c/78408
* tree-ssa-ccp.c: Include tree-dfa.h.
(optimize_memcpy): New function.
(pass_fold_builtins::execute): Use it. Remove useless conditional
break after BUILT_IN_VA_*.
* gcc.dg/pr78408-1.c: New test.
* gcc.dg/pr78408-2.c: New test.
--- gcc/tree-ssa-ccp.c.jj 2016-12-16 11:24:31.495987909 +0100
+++ gcc/tree-ssa-ccp.c 2016-12-16 14:41:22.572861225 +0100
@@ -143,6 +143,7 @@ along with GCC; see the file COPYING3.
#include "stor-layout.h"
#include "optabs-query.h"
#include "tree-ssa-ccp.h"
+#include "tree-dfa.h"
/* Possible lattice values. */
typedef enum
@@ -2933,6 +2934,119 @@ optimize_atomic_bit_test_and (gimple_stm
release_ssa_name (lhs);
}
+/* Optimize
+ a = {};
+ b = a;
+ into
+ a = {};
+ b = {};
+ Similarly for memset (&a, ..., sizeof (a)); instead of a = {};
+ and/or memcpy (&b, &a, sizeof (a)); instead of b = a; */
+
+static void
+optimize_memcpy (gimple_stmt_iterator *gsip, tree dest, tree src, tree len)
+{
+ gimple *stmt = gsi_stmt (*gsip);
+ if (gimple_has_volatile_ops (stmt))
+ return;
+
+ tree vuse = gimple_vuse (stmt);
+ if (vuse == NULL)
+ return;
+
+ gimple *defstmt = SSA_NAME_DEF_STMT (vuse);
+ tree src2 = NULL_TREE, len2 = NULL_TREE;
+ HOST_WIDE_INT offset, offset2;
+ tree val = integer_zero_node;
+ if (gimple_store_p (defstmt)
+ && gimple_assign_single_p (defstmt)
+ && TREE_CODE (gimple_assign_rhs1 (defstmt)) == CONSTRUCTOR
+ && !gimple_clobber_p (defstmt))
+ src2 = gimple_assign_lhs (defstmt);
+ else if (gimple_call_builtin_p (defstmt, BUILT_IN_MEMSET)
+ && TREE_CODE (gimple_call_arg (defstmt, 0)) == ADDR_EXPR
+ && TREE_CODE (gimple_call_arg (defstmt, 1)) == INTEGER_CST)
+ {
+ src2 = TREE_OPERAND (gimple_call_arg (defstmt, 0), 0);
+ len2 = gimple_call_arg (defstmt, 2);
+ val = gimple_call_arg (defstmt, 1);
+ /* For non-0 val, we'd have to transform stmt from assignment
+ into memset (only if dest is addressable). */
+ if (!integer_zerop (val) && is_gimple_assign (stmt))
+ src2 = NULL_TREE;
+ }
+
+ if (src2 == NULL_TREE)
+ return;
+
+ if (len == NULL_TREE)
+ len = (TREE_CODE (src) == COMPONENT_REF
+ ? DECL_SIZE_UNIT (TREE_OPERAND (src, 1))
+ : TYPE_SIZE_UNIT (TREE_TYPE (src)));
+ if (len2 == NULL_TREE)
+ len2 = (TREE_CODE (src2) == COMPONENT_REF
+ ? DECL_SIZE_UNIT (TREE_OPERAND (src2, 1))
+ : TYPE_SIZE_UNIT (TREE_TYPE (src2)));
+ if (len == NULL_TREE
+ || TREE_CODE (len) != INTEGER_CST
+ || len2 == NULL_TREE
+ || TREE_CODE (len2) != INTEGER_CST)
+ return;
+
+ src = get_addr_base_and_unit_offset (src, &offset);
+ src2 = get_addr_base_and_unit_offset (src2, &offset2);
+ if (src == NULL_TREE
+ || src2 == NULL_TREE
+ || offset < offset2)
+ return;
+
+ if (!operand_equal_p (src, src2, 0))
+ return;
+
+ /* [ src + offset2, src + offset2 + len2 - 1 ] is set to val.
+ Make sure that
+ [ src + offset, src + offset + len - 1 ] is a subset of that. */
+ if (wi::to_offset (len) + (offset - offset2) > wi::to_offset (len2))
+ return;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "Simplified\n ");
+ print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+ fprintf (dump_file, "after previous\n ");
+ print_gimple_stmt (dump_file, defstmt, 0, dump_flags);
+ }
+
+ /* For simplicity, don't change the kind of the stmt,
+ turn dest = src; into dest = {}; and memcpy (&dest, &src, len);
+ into memset (&dest, val, len);
+ In theory we could change dest = src into memset if dest
+ is addressable (maybe beneficial if val is not 0), or
+ memcpy (&dest, &src, len) into dest = {} if len is the size
+ of dest, dest isn't volatile. */
+ if (is_gimple_assign (stmt))
+ {
+ tree ctor = build_constructor (TREE_TYPE (dest), NULL);
+ gimple_assign_set_rhs_from_tree (gsip, ctor);
+ update_stmt (stmt);
+ }
+ else /* If stmt is memcpy, transform it into memset. */
+ {
+ gcall *call = as_a <gcall *> (stmt);
+ tree fndecl = builtin_decl_implicit (BUILT_IN_MEMSET);
+ gimple_call_set_fndecl (call, fndecl);
+ gimple_call_set_fntype (call, TREE_TYPE (fndecl));
+ gimple_call_set_arg (call, 1, val);
+ update_stmt (stmt);
+ }
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "into\n ");
+ print_gimple_stmt (dump_file, stmt, 0, dump_flags);
+ }
+}
+
/* A simple pass that attempts to fold all builtin functions. This pass
is run after we've propagated as many constants as we can. */
@@ -2999,6 +3113,9 @@ pass_fold_builtins::execute (function *f
continue;
}
}
+ else if (gimple_assign_load_p (stmt) && gimple_store_p (stmt))
+ optimize_memcpy (&i, gimple_assign_lhs (stmt),
+ gimple_assign_rhs1 (stmt), NULL_TREE);
gsi_next (&i);
continue;
}
@@ -3114,14 +3231,25 @@ pass_fold_builtins::execute (function *f
false, false);
break;
+ case BUILT_IN_MEMCPY:
+ if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL)
+ && TREE_CODE (gimple_call_arg (stmt, 0)) == ADDR_EXPR
+ && TREE_CODE (gimple_call_arg (stmt, 1)) == ADDR_EXPR
+ && TREE_CODE (gimple_call_arg (stmt, 2)) == INTEGER_CST)
+ {
+ tree dest = TREE_OPERAND (gimple_call_arg (stmt, 0), 0);
+ tree src = TREE_OPERAND (gimple_call_arg (stmt, 1), 0);
+ tree len = gimple_call_arg (stmt, 2);
+ optimize_memcpy (&i, dest, src, len);
+ }
+ break;
+
case BUILT_IN_VA_START:
case BUILT_IN_VA_END:
case BUILT_IN_VA_COPY:
/* These shouldn't be folded before pass_stdarg. */
result = optimize_stdarg_builtin (stmt);
- if (result)
- break;
- /* FALLTHRU */
+ break;
default:;
}
--- gcc/testsuite/gcc.dg/pr78408-1.c.jj 2016-12-16 14:33:38.890063632 +0100
+++ gcc/testsuite/gcc.dg/pr78408-1.c 2016-12-16 14:33:38.890063632 +0100
@@ -0,0 +1,88 @@
+/* PR c/78408 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fab1-details" } */
+/* { dg-final { scan-tree-dump-times "after previous" 17 "fab1" } } */
+
+struct S { char a[32]; };
+struct T { char a[65536]; };
+void bar (int, struct S *, struct S *, struct T *, struct T *);
+void baz (char *, char *);
+
+void
+f1 (void)
+{
+ struct S a, b;
+ struct T c, d;
+ a = b = (struct S) {};
+ c = d = (struct T) {};
+ bar (1, &a, &b, &c, &d);
+}
+
+void
+f2 (void)
+{
+ struct S a, b;
+ struct T c, d;
+ b = (struct S) {};
+ a = b;
+ d = (struct T) {};
+ c = d;
+ bar (2, &a, &b, &c, &d);
+}
+
+void
+f3 (void)
+{
+ struct S a, b;
+ struct T c, d;
+ __builtin_memset (&b, 0, sizeof (b));
+ a = b;
+ __builtin_memset (&d, 0, sizeof (d));
+ c = d;
+ bar (3, &a, &b, &c, &d);
+}
+
+
+void
+f4 (void)
+{
+ struct S a, b;
+ struct T c, d;
+ b = (struct S) {};
+ __builtin_memcpy (&a, &b, sizeof (b));
+ d = (struct T) {};
+ __builtin_memcpy (&c, &d, sizeof (d));
+ bar (4, &a, &b, &c, &d);
+}
+
+void
+f5 (void)
+{
+ struct S a, b;
+ struct T c, d;
+ __builtin_memset (&b, 0, sizeof (b));
+ __builtin_memcpy (&a, &b, sizeof (b));
+ __builtin_memset (&d, 0, sizeof (d));
+ __builtin_memcpy (&c, &d, sizeof (d));
+ bar (5, &a, &b, &c, &d);
+}
+
+void
+f6 (void)
+{
+ struct S a, b, e, g;
+ struct T c, d, f, h;
+ g = e = a = b = (struct S) {};
+ h = f = c = d = (struct T) {};
+ bar (6, &a, &b, &c, &d);
+ bar (6, &e, &g, &f, &h);
+}
+
+void
+f7 (void)
+{
+ char a[64], b[64];
+ __builtin_memset (a + 13, 2, 27);
+ __builtin_memcpy (b + 4, a + 17, 23);
+ baz (a, b);
+}
--- gcc/testsuite/gcc.dg/pr78408-2.c.jj 2016-12-16 14:33:38.890063632 +0100
+++ gcc/testsuite/gcc.dg/pr78408-2.c 2016-12-16 14:33:38.890063632 +0100
@@ -0,0 +1,39 @@
+/* PR c/78408 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fab1-details" } */
+/* { dg-final { scan-tree-dump-not "after previous" "fab1" } } */
+
+struct S { char a[32]; };
+struct T { char a[65536]; };
+void bar (int, struct S *, struct S *, struct T *, struct T *);
+void baz (char *, char *);
+
+void
+f1 (void)
+{
+ struct S a, b;
+ struct T c, d;
+ __builtin_memset (&b, 2, sizeof (b));
+ a = b;
+ __builtin_memset (&d, 3, sizeof (d));
+ c = d;
+ bar (3, &a, &b, &c, &d);
+}
+
+void
+f2 (void)
+{
+ char a[64], b[64];
+ __builtin_memset (a + 13, 2, 27);
+ __builtin_memcpy (b + 4, a + 17, 24);
+ baz (a, b);
+}
+
+void
+f3 (void)
+{
+ char a[64], b[64];
+ __builtin_memset (a + 13, 2, 27);
+ __builtin_memcpy (b + 4, a + 12, 5);
+ baz (a, b);
+}
Jakub
