On Thu, 4 Nov 2021, Jakub Jelinek wrote:
> Hi!
>
> When users don't use constexpr everywhere in initialization of namespace
> scope non-comdat vars and the initializers aren't constant when FE is
> looking at them, the FE performs dynamic initialization of those variables.
> But after inlining and some constant propagation, we often end up with
> just storing constants into those variables in the _GLOBAL__sub_I_*
> constructor.
> C++ gives us permission to change some of that dynamic initialization
> back into static initialization - https://eel.is/c++draft/basic.start.static#3
> For classes that need (dynamic) construction, I believe access to some var
> from other dynamic construction before that var is constructed is UB, but
> as the example in the above mentioned spot of C++:
> inline double fd() { return 1.0; }
> extern double d1;
> double d2 = d1; // unspecified:
> // either statically initialized to 0.0 or
> // dynamically initialized to 0.0 if d1 is
> // dynamically initialized, or 1.0 otherwise
> double d1 = fd(); // either initialized statically or dynamically to 1.0
> some vars can be used before they are dynamically initialized and the
> implementation can still optimize those into static initialization.
>
> The following patch attempts to optimize some such cases back into
> DECL_INITIAL initializers and where possible (originally const vars without
> mutable members) put those vars back to .rodata etc.
>
> Because we put all dynamic initialization from a single TU into one single
> function (well, originally one function per priority but typically inline
> those back into one function), we can either have a simpler approach
> (from the PR it seems that is what LLVM uses) where either we manage to
> optimize all dynamic initializers into constant in the TU, or nothing,
> or by adding some markup - in the form of a pair of internal functions in
> this patch - around each dynamic initialization that can be optimized,
> we can optimize each dynamic initialization separately.
>
> The patch adds a new pass that is invoked (through gate check) only on
> DECL_ARTIFICIAL DECL_STATIC_CONSTRUCTOR functions, and looks there for
> sequences like:
> .DYNAMIC_INIT_START (&b, 0);
> b = 1;
> .DYNAMIC_INIT_END (&b);
> or
> .DYNAMIC_INIT_START (&e, 1);
> # DEBUG this => &e.f
> MEM[(struct S *)&e + 4B] ={v} {CLOBBER};
> MEM[(struct S *)&e + 4B].a = 1;
> MEM[(struct S *)&e + 4B].b = 2;
> MEM[(struct S *)&e + 4B].c = 3;
> # DEBUG BEGIN_STMT
> MEM[(struct S *)&e + 4B].d = 6;
> # DEBUG this => NULL
> .DYNAMIC_INIT_END (&e);
So with
+/* Mark start and end of dynamic initialization of a variable. */
+DEF_INTERNAL_FN (DYNAMIC_INIT_START, ECF_LEAF | ECF_NOTHROW, ". r ")
+DEF_INTERNAL_FN (DYNAMIC_INIT_END, ECF_LEAF | ECF_NOTHROW, ". r ")
there's nothing preventing code motion of unrelated stmts into
the block, but that should be harmless. What it also does
is make 'e' aliased (because it's address is now taken), probably
relevant only for IPA/LTO or for statics.
The setup does not prevent CSEing the inits with uses from another
initializer - probably OK as well (if not then .DYNAMIC_INIT_END
should also be considered writing to 'e').
". r " also means it clobbers and uses all global memory, I think
we'd like to have it const + looping-pure-or-const. ".cr " would
possibly achieve this, not sure about the looping part.
> (where between the pair of markers everything is either debug stmts or
> stores of constants into the variables or their parts).
> The pass needs to be done late enough so that after IPA all the needed
> constant propagation and perhaps loop unrolling is done, on the other
> side should be early enough so that if we can't optimize it, we can
> remove those .DYNAMIC_INIT* internal calls that could prevent some
> further optimizations (they have fnspec such that they pretend to read
> the corresponding variable).
>
> Currently the optimization is only able to optimize cases where the whole
> variable is stored in a single store (typically scalar variables), or
> uses the native_{encode,interpret}* infrastructure to create or update
> the CONSTRUCTOR. This means that except for the first category, we can't
> right now handle unions or anything that needs relocations (vars containing
> pointers to other vars or references).
> I think it would be nice to incrementally add before the native_* fallback
> some attempt to just create or update a CONSTRUCTOR if possible. If we only
> see var.a.b.c.d[10].e = const; style of stores, this shouldn't be that hard
> as the whole access path is recorded there and we'd just need to decide what
> to do with unions if two or more union members are accessed. And do a deep
> copy of the CONSTRUCTOR and try to efficiently update the copy afterwards
> (the CONSTRUCTORs should be sorted on increasing offsets of the
> members/elements, so doing an ordered vec insertion might not be the best
> idea). But MEM_REFs complicate this, parts or all of the access path
> is lost. For non-unions in most cases we could try to guess which field
> it is (do we have some existing function to do that? I vaguely remember
> we've been doing that in some cases in the past in some folding but stopped
> doing so) but with unions it will be harder or impossible.
I suppose we could, at least for non-overlapping inits, create a
new aggregate type on the fly to be able to compose the CTOR and then
view-convert it to the decls type. Would need to check that
a CTOR wrapped in a V_C_E is handled OK by varasm of course.
An alternative way of recording the initializer (maybe just emit
it right away into asm?) would be another possibility.
I also note that loops are quite common in some initializers so more
aggressively unrolling those for initializations might be a good
idea as well.
> As the middle-end can't easily differentiate between const variables without
> and with mutable members, both of those will have TREE_READONLY on the
> var decl clear (because of dynamic initialization) and TYPE_READONLY set
> on the type, the patch remembers this in an extra argument to
> .DYNAMIC_INIT_START (true if it is ok to set TREE_READONLY on the var decl
> back if the var dynamic initialization could be optimized into DECL_INITIAL).
> Thinking more about it, I'm not sure about const vars without mutable
> members with non-trivial destructors, do we register their dtors dynamically
> through __cxa_atexit in the ctors (that would mean the optimization
> currently punts on them), or not (in that case we could put it into .rodata
> even when the dtor will want to perhaps write to them)?
I think anything like this asks for doing the whole thing at IPA level
to see which functions are "initialization" and thus need not considered
writing when the initializer is made static.
That said, do we want to record the fact that we guarded init
with .DYNAMIC_INIT_* on the varpool node? I think we want a flag
in struct function or in the cgraph node to tell whether there's
a .DYNAMIC_INIT_* in it to avoid the whole function walk of
pass_dyninit::execute which for most functions will be a noop.
Is there any reason you run the pass before pass_store_merging? It
does seem to rely on it to some extent - in fact it looks like
both might be married somehow? I don't think that doing it "early"
for the sake of loop optimizations is worth the trouble (doing
it way earlier for the sake of IPA would be another thing though).
> Anyway, forgot to do another set of bootstraps with gathering statistics how
> many vars were optimized, so just trying to figure it out from the sizes of
> _GLOBAL__sub_I_* functions:
>
> # Without patch, x86_64-linux cc1plus
> $ readelf -Ws obj50/gcc/cc1plus | grep ' _GLOBAL__sub_I_' | awk
> 'BEGIN{I=0}{I=I+$3}END{print I}'
> 13934
> # With the patch, x86_64-linux cc1plus
> $ readelf -Ws obj52/gcc/cc1plus | grep ' _GLOBAL__sub_I_' | awk
> 'BEGIN{I=0}{I=I+$3}END{print I}'
> 6966
> # Without patch, i686-linux cc1plus
> $ readelf -Ws obj51/gcc/cc1plus | grep ' _GLOBAL__sub_I_' | awk
> 'BEGIN{I=0}{I=I+$3}END{print I}'
> 24158
> # With the patch, i686-linux cc1plus
> $ readelf -Ws obj53/gcc/cc1plus | grep ' _GLOBAL__sub_I_' | awk
> 'BEGIN{I=0}{I=I+$3}END{print I}'
> 10536
>
> That seems like a huge improvement, although on a closer look, most of that
> saving is from just one TU:
> $ readelf -Ws obj50/gcc/i386-options.o | grep ' _GLOBAL__sub_I_' | awk
> '{print $3}'
> 6693
> $ readelf -Ws obj52/gcc/i386-options.o | grep ' _GLOBAL__sub_I_' | awk
> '{print $3}'
> 1
> $ readelf -Ws obj51/gcc/i386-options.o | grep ' _GLOBAL__sub_I_' | awk
> '{print $3}'
> 13001
> $ readelf -Ws obj53/gcc/i386-options.o | grep ' _GLOBAL__sub_I_' | awk
> '{print $3}'
> 1
> So, the shrinking on all the dynamic initialization functions except
> i386-options.o is:
> 7241 -> 6965 for 64-bit and
> 11157 -> 10535 for 32-bit.
> Will try to use constexpr for i386-options.c later today.
>
> Another optimization that could be useful but not sure if it can be easily
> done is if we before expansion of the _GLOBAL__sub_I_* functions end up with
> nothing in their body (that's those 1 byte functions on x86) perhaps either
> not emit those functions at all or at least don't register them in
> .init_array etc. so that cycles aren't wasted at runtime:
> $ readelf -Ws obj50/gcc/{*,*/*}.o | grep ' _GLOBAL__sub_I_' | awk '($3 ==
> 1){print $3}' | wc -l
> 4
> $ readelf -Ws obj52/gcc/{*,*/*}.o | grep ' _GLOBAL__sub_I_' | awk '($3 ==
> 1){print $3}' | wc -l
> 87
> $ readelf -Ws obj51/gcc/{*,*/*}.o | grep ' _GLOBAL__sub_I_' | awk '($3 ==
> 1){print $3}' | wc -l
> 4
> $ readelf -Ws obj53/gcc/{*,*/*}.o | grep ' _GLOBAL__sub_I_' | awk '($3 ==
> 1){print $3}' | wc -l
> 84
>
> Also, wonder if I should add some new -f* option to control the optimization
> or doing it always at -O+ with -fdisable-tree-pass-dyninit as a way to
> disable it is good enough, and whether the 1024 hardcoded constant
> (upper bound on optimized size so that we don't spend huge amounts of
> compile time trying to optimize initializers of gigabyte sizes) shouldn't be
> a param.
I also see you gate .DYNAMIC_INIT_* creation on 'optimize' but only
scheudle the pass in the O1+ pipeline, missing out -Og. I suppose
for -Og not creating .DYNAMIC_INIT_* would be reasonable.
Some more comments inline.
> Bootstrapped/regtested on x86_64-linux and i686-linux.
>
> 2021-11-04 Jakub Jelinek <ja...@redhat.com>
>
> PR c++/102876
> gcc/
> * internal-fn.def (DYNAMIC_INIT_START, DYNAMIC_INIT_END): New internal
> functions.
> * internal-fn.c (expand_DYNAMIC_INIT_START, expand_DYNAMIC_INIT_END):
> New functions.
> * tree-pass.h (make_pass_dyninit): Declare.
> * passes.def (pass_dyninit): Add after dce4.
> * gimple-ssa-store-merging.c (pass_data_dyninit): New variable.
> (class pass_dyninit): New type.
> (pass_dyninit::execute): New method.
> (make_pass_dyninit): New function.
> gcc/cp/
> * decl2.c (one_static_initialization_or_destruction): Emit
> .DYNAMIC_INIT_START and .DYNAMIC_INIT_END internal calls around
> dynamic initialization of variables that don't need a guard.
> gcc/testsuite/
> * g++.dg/opt/init3.C: New test.
>
> --- gcc/internal-fn.def.jj 2021-11-02 09:05:47.029664211 +0100
> +++ gcc/internal-fn.def 2021-11-02 12:40:38.702436113 +0100
> @@ -367,6 +367,10 @@ DEF_INTERNAL_FN (PHI, 0, NULL)
> automatic variable. */
> DEF_INTERNAL_FN (DEFERRED_INIT, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
>
> +/* Mark start and end of dynamic initialization of a variable. */
> +DEF_INTERNAL_FN (DYNAMIC_INIT_START, ECF_LEAF | ECF_NOTHROW, ". r ")
> +DEF_INTERNAL_FN (DYNAMIC_INIT_END, ECF_LEAF | ECF_NOTHROW, ". r ")
> +
> /* DIM_SIZE and DIM_POS return the size of a particular compute
> dimension and the executing thread's position within that
> dimension. DIM_POS is pure (and not const) so that it isn't
> --- gcc/internal-fn.c.jj 2021-11-02 09:05:47.029664211 +0100
> +++ gcc/internal-fn.c 2021-11-02 12:40:38.703436099 +0100
> @@ -3485,6 +3485,16 @@ expand_CO_ACTOR (internal_fn, gcall *)
> gcc_unreachable ();
> }
>
> +static void
> +expand_DYNAMIC_INIT_START (internal_fn, gcall *)
> +{
> +}
> +
> +static void
> +expand_DYNAMIC_INIT_END (internal_fn, gcall *)
> +{
> +}
> +
> /* Expand a call to FN using the operands in STMT. FN has a single
> output operand and NARGS input operands. */
>
> --- gcc/tree-pass.h.jj 2021-10-28 11:29:01.891721153 +0200
> +++ gcc/tree-pass.h 2021-11-02 14:15:00.139185088 +0100
> @@ -445,6 +445,7 @@ extern gimple_opt_pass *make_pass_cse_re
> extern gimple_opt_pass *make_pass_cse_sincos (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_optimize_bswap (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_store_merging (gcc::context *ctxt);
> +extern gimple_opt_pass *make_pass_dyninit (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_optimize_widening_mul (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_warn_function_return (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_warn_function_noreturn (gcc::context
> *ctxt);
> --- gcc/passes.def.jj 2021-11-01 14:37:06.685853324 +0100
> +++ gcc/passes.def 2021-11-02 14:23:47.836715821 +0100
> @@ -261,6 +261,7 @@ along with GCC; see the file COPYING3.
> NEXT_PASS (pass_tsan);
> NEXT_PASS (pass_dse);
> NEXT_PASS (pass_dce);
> + NEXT_PASS (pass_dyninit);
> /* Pass group that runs when 1) enabled, 2) there are loops
> in the function. Make sure to run pass_fix_loops before
> to discover/remove loops before running the gate function
> --- gcc/gimple-ssa-store-merging.c.jj 2021-09-01 12:06:19.488211919 +0200
> +++ gcc/gimple-ssa-store-merging.c 2021-11-03 18:02:55.190015359 +0100
> @@ -170,6 +170,8 @@
> #include "optabs-tree.h"
> #include "dbgcnt.h"
> #include "selftest.h"
> +#include "cgraph.h"
> +#include "varasm.h"
>
> /* The maximum size (in bits) of the stores this pass should generate. */
> #define MAX_STORE_BITSIZE (BITS_PER_WORD)
> @@ -5465,6 +5467,334 @@ pass_store_merging::execute (function *f
> return 0;
> }
>
> +/* Pass to optimize C++ dynamic initialization. */
> +
> +const pass_data pass_data_dyninit = {
> + GIMPLE_PASS, /* type */
> + "dyninit", /* name */
> + OPTGROUP_NONE, /* optinfo_flags */
> + TV_GIMPLE_STORE_MERGING, /* tv_id */
> + PROP_ssa, /* properties_required */
> + 0, /* properties_provided */
> + 0, /* properties_destroyed */
> + 0, /* todo_flags_start */
> + 0, /* todo_flags_finish */
> +};
> +
> +class pass_dyninit : public gimple_opt_pass
> +{
> +public:
> + pass_dyninit (gcc::context *ctxt)
> + : gimple_opt_pass (pass_data_dyninit, ctxt)
> + {
> + }
> +
> + virtual bool
> + gate (function *fun)
> + {
> + return (DECL_ARTIFICIAL (fun->decl)
> + && DECL_STATIC_CONSTRUCTOR (fun->decl)
> + && optimize);
> + }
> +
> + virtual unsigned int execute (function *);
> +}; // class pass_dyninit
> +
> +unsigned int
> +pass_dyninit::execute (function *fun)
> +{
> + basic_block bb;
> + auto_vec<gimple *, 32> ifns;
> + hash_map<tree, gimple *> *map = NULL;
> + auto_vec<tree, 32> vars;
> + gimple **cur = NULL;
> + bool ssdf_calls = false;
> +
> + FOR_EACH_BB_FN (bb, fun)
> + {
> + for (gimple_stmt_iterator gsi = gsi_after_labels (bb);
> + !gsi_end_p (gsi); gsi_next (&gsi))
> + {
> + gimple *stmt = gsi_stmt (gsi);
> + if (is_gimple_debug (stmt))
> + continue;
> +
> + /* The C++ FE can wrap dynamic initialization of certain
> + variables with a pair of iternal function calls, like:
> + .DYNAMIC_INIT_START (&b, 0);
> + b = 1;
> + .DYNAMIC_INIT_END (&b);
> +
> + or
> + .DYNAMIC_INIT_START (&e, 1);
> + # DEBUG this => &e.f
> + MEM[(struct S *)&e + 4B] ={v} {CLOBBER};
> + MEM[(struct S *)&e + 4B].a = 1;
> + MEM[(struct S *)&e + 4B].b = 2;
> + MEM[(struct S *)&e + 4B].c = 3;
> + # DEBUG BEGIN_STMT
> + MEM[(struct S *)&e + 4B].d = 6;
> + # DEBUG this => NULL
> + .DYNAMIC_INIT_END (&e);
> +
> + Verify if there are only stores of constants to the corresponding
> + variable or parts of that variable and if so, try to reconstruct
> + a static initializer from the static initializer if any and
> + the constant stores into the variable. This is permitted by
> + [basic.start.static]/3. */
> + if (is_gimple_call (stmt))
> + {
> + if (gimple_call_internal_p (stmt, IFN_DYNAMIC_INIT_START))
this overload already tests is_gimple_call
> + {
> + ifns.safe_push (stmt);
> + if (cur)
> + *cur = NULL;
> + tree arg = gimple_call_arg (stmt, 0);
> + gcc_assert (TREE_CODE (arg) == ADDR_EXPR
> + && DECL_P (TREE_OPERAND (arg, 0)));
> + tree var = TREE_OPERAND (arg, 0);
> + gcc_checking_assert (is_global_var (var));
> + varpool_node *node = varpool_node::get (var);
> + if (node == NULL
> + || node->in_other_partition
> + || TREE_ASM_WRITTEN (var)
> + || DECL_SIZE_UNIT (var) == NULL_TREE
> + || !tree_fits_uhwi_p (DECL_SIZE_UNIT (var))
> + || tree_to_uhwi (DECL_SIZE_UNIT (var)) > 1024
this should maybe be a --param?
Did you do any statistics on things other than GCC what of the various
checks prevents eliding the dynamic initialization and which of those
we could mitigate in the future?
> + || TYPE_SIZE_UNIT (TREE_TYPE (var)) == NULL_TREE
> + || !tree_int_cst_equal (TYPE_SIZE_UNIT (TREE_TYPE (var)),
> + DECL_SIZE_UNIT (var)))
> + continue;
> + if (map == NULL)
> + map = new hash_map<tree, gimple *> (61);
> + bool existed_p;
> + cur = &map->get_or_insert (var, &existed_p);
> + if (existed_p)
> + {
> + /* Punt if we see more than one .DYNAMIC_INIT_START
> + internal call for the same variable. */
how can this happen?
> + *cur = NULL;
> + cur = NULL;
> + }
> + else
> + {
> + *cur = stmt;
> + vars.safe_push (var);
> + }
> + continue;
> + }
> + else if (gimple_call_internal_p (stmt, IFN_DYNAMIC_INIT_END))
> + {
> + ifns.safe_push (stmt);
> + tree arg = gimple_call_arg (stmt, 0);
> + gcc_assert (TREE_CODE (arg) == ADDR_EXPR
> + && DECL_P (TREE_OPERAND (arg, 0)));
> + tree var = TREE_OPERAND (arg, 0);
> + gcc_checking_assert (is_global_var (var));
> + if (cur)
> + {
> + /* Punt if .DYNAMIC_INIT_END call argument doesn't
> + pair with .DYNAMIC_INIT_START. */
> + if (vars.last () != var)
> + *cur = NULL;
> + cur = NULL;
> + }
> + continue;
> + }
> +
> + /* Punt if we see any artificial
> + __static_initialization_and_destruction_* calls, e.g. if
> + it would be partially inlined, because we wouldn't then see
> + all .DYNAMIC_INIT_* calls. */
> + tree fndecl = gimple_call_fndecl (stmt);
> + if (fndecl
> + && DECL_ARTIFICIAL (fndecl)
> + && DECL_NAME (fndecl)
> + && startswith (IDENTIFIER_POINTER (DECL_NAME (fndecl)),
> + "__static_initialization_and_destruction_"))
> + ssdf_calls = true;
Ugh, that looks unreliable - but how's that a problem if we saw
both START/END ifns for a decl?
> + }
> + if (cur)
> + {
> + if (store_valid_for_store_merging_p (stmt))
> + {
> + tree lhs = gimple_assign_lhs (stmt);
> + tree rhs = gimple_assign_rhs1 (stmt);
> + poly_int64 bitsize, bitpos;
> + HOST_WIDE_INT ibitsize, ibitpos;
> + machine_mode mode;
> + int unsignedp, reversep, volatilep = 0;
> + tree offset;
> + tree var = vars.last ();
> + if (rhs_valid_for_store_merging_p (rhs)
> + && get_inner_reference (lhs, &bitsize, &bitpos, &offset,
> + &mode, &unsignedp, &reversep,
> + &volatilep) == var
> + && !reversep
> + && !volatilep
> + && (offset == NULL_TREE || integer_zerop (offset))
> + && bitsize.is_constant (&ibitsize)
> + && bitpos.is_constant (&ibitpos)
> + && ibitpos >= 0
> + && ibitsize <= tree_to_shwi (DECL_SIZE (var))
> + && ibitsize + ibitpos <= tree_to_shwi (DECL_SIZE (var)))
> + continue;
> + }
> + *cur = NULL;
> + cur = NULL;
> + }
> + }
> + if (cur)
> + {
> + *cur = NULL;
> + cur = NULL;
> + }
> + }
> + if (map && !ssdf_calls)
> + {
> + for (tree var : vars)
> + {
> + gimple *g = *map->get (var);
> + if (g == NULL)
> + continue;
> + varpool_node *node = varpool_node::get (var);
> + node->get_constructor ();
> + tree init = DECL_INITIAL (var);
> + if (init == NULL)
> + init = build_zero_cst (TREE_TYPE (var));
> + gimple_stmt_iterator gsi = gsi_for_stmt (g);
> + unsigned char *buf = NULL;
> + unsigned int buf_size = tree_to_uhwi (DECL_SIZE_UNIT (var));
> + bool buf_valid = false;
> + do
> + {
> + gsi_next (&gsi);
> + gimple *stmt = gsi_stmt (gsi);
> + if (is_gimple_debug (stmt))
> + continue;
> + if (is_gimple_call (stmt))
> + break;
> + if (gimple_clobber_p (stmt))
> + continue;
> + tree lhs = gimple_assign_lhs (stmt);
> + tree rhs = gimple_assign_rhs1 (stmt);
> + if (lhs == var)
> + {
> + /* Simple assignment to the whole variable.
> + rhs is the initializer. */
> + buf_valid = false;
> + init = rhs;
> + continue;
> + }
> + poly_int64 bitsize, bitpos;
> + machine_mode mode;
> + int unsignedp, reversep, volatilep = 0;
> + tree offset;
> + get_inner_reference (lhs, &bitsize, &bitpos, &offset,
> + &mode, &unsignedp, &reversep, &volatilep);
> + HOST_WIDE_INT ibitsize = bitsize.to_constant ();
> + HOST_WIDE_INT ibitpos = bitpos.to_constant ();
> + if (BYTES_BIG_ENDIAN != WORDS_BIG_ENDIAN
> + || CHAR_BIT != 8
> + || BITS_PER_UNIT != 8)
> + {
> + g = NULL;
> + break;
> + }
> + if (!buf_valid)
> + {
> + if (buf == NULL)
> + buf = XNEWVEC (unsigned char, buf_size * 2);
> + memset (buf, 0, buf_size);
> + if (native_encode_initializer (init, buf, buf_size)
> + != (int) buf_size)
> + {
> + g = NULL;
> + break;
> + }
> + buf_valid = true;
> + }
> + /* Otherwise go through byte representation. */
> + if (!encode_tree_to_bitpos (rhs, buf, ibitsize,
> + ibitpos, buf_size))
> + {
> + g = NULL;
> + break;
> + }
> + }
> + while (1);
> + if (g == NULL)
> + {
> + XDELETE (buf);
> + continue;
> + }
> + if (buf_valid)
> + {
> + init = native_interpret_aggregate (TREE_TYPE (var), buf, 0,
> + buf_size);
> + if (init)
> + {
> + /* Verify the dynamic initialization doesn't e.g. set
> + some padding bits to non-zero by trying to encode
> + it again and comparing. */
> + memset (buf + buf_size, 0, buf_size);
> + if (native_encode_initializer (init, buf + buf_size,
> + buf_size) != (int) buf_size
> + || memcmp (buf, buf + buf_size, buf_size) != 0)
> + init = NULL_TREE;
> + }
> + }
> + XDELETE (buf);
> + if (!init || !initializer_constant_valid_p (init, TREE_TYPE (var)))
> + continue;
> + if (integer_nonzerop (gimple_call_arg (g, 1)))
> + TREE_READONLY (var) = 1;
> + if (dump_file)
> + {
> + fprintf (dump_file, "dynamic initialization of ");
> + print_generic_stmt (dump_file, var, TDF_SLIM);
> + fprintf (dump_file, " optimized into: ");
> + print_generic_stmt (dump_file, init, TDF_SLIM);
> + if (TREE_READONLY (var))
> + fprintf (dump_file, " and making it read-only\n");
> + fprintf (dump_file, "\n");
> + }
> + if (initializer_zerop (init))
> + DECL_INITIAL (var) = NULL_TREE;
> + else
> + DECL_INITIAL (var) = init;
> + gsi = gsi_for_stmt (g);
> + gsi_next (&gsi);
> + do
> + {
> + gimple *stmt = gsi_stmt (gsi);
> + if (is_gimple_debug (stmt))
> + {
> + gsi_next (&gsi);
> + continue;
> + }
> + if (is_gimple_call (stmt))
> + break;
> + /* Remove now all the stores for the dynamic initialization. */
> + unlink_stmt_vdef (stmt);
> + gsi_remove (&gsi, true);
> + if (gimple_vdef (stmt))
> + release_ssa_name (gimple_vdef (stmt));
release_defs () should do the trick
> + }
> + while (1);
> + }
> + }
> + delete map;
> + for (gimple *g : ifns)
> + {
> + gimple_stmt_iterator gsi = gsi_for_stmt (g);
> + unlink_stmt_vdef (g);
> + gsi_remove (&gsi, true);
> + if (gimple_vdef (g))
> + release_ssa_name (gimple_vdef (g));
likewise.
> + }
> + return 0;
> +}
> } // anon namespace
>
> /* Construct and return a store merging pass object. */
> @@ -5475,6 +5805,14 @@ make_pass_store_merging (gcc::context *c
> return new pass_store_merging (ctxt);
> }
>
> +/* Construct and return a dyninit pass object. */
> +
> +gimple_opt_pass *
> +make_pass_dyninit (gcc::context *ctxt)
> +{
> + return new pass_dyninit (ctxt);
> +}
> +
> #if CHECKING_P
>
> namespace selftest {
> --- gcc/cp/decl2.c.jj 2021-11-02 09:05:47.004664566 +0100
> +++ gcc/cp/decl2.c 2021-11-03 17:18:11.395288518 +0100
> @@ -4133,13 +4133,36 @@ one_static_initialization_or_destruction
> {
> if (init)
> {
> + bool sanitize = sanitize_flags_p (SANITIZE_ADDRESS, decl);
> + if (optimize && guard == NULL_TREE && !sanitize)
> + {
> + tree t = build_fold_addr_expr (decl);
> + tree type = TREE_TYPE (decl);
> + tree is_const
> + = constant_boolean_node (TYPE_READONLY (type)
> + && !cp_has_mutable_p (type),
> + boolean_type_node);
> + t = build_call_expr_internal_loc (DECL_SOURCE_LOCATION (decl),
> + IFN_DYNAMIC_INIT_START,
> + void_type_node, 2, t,
> + is_const);
> + finish_expr_stmt (t);
> + }
> finish_expr_stmt (init);
> - if (sanitize_flags_p (SANITIZE_ADDRESS, decl))
> + if (sanitize)
> {
> varpool_node *vnode = varpool_node::get (decl);
> if (vnode)
> vnode->dynamically_initialized = 1;
> }
> + else if (optimize && guard == NULL_TREE)
> + {
> + tree t = build_fold_addr_expr (decl);
> + t = build_call_expr_internal_loc (DECL_SOURCE_LOCATION (decl),
> + IFN_DYNAMIC_INIT_END,
> + void_type_node, 1, t);
> + finish_expr_stmt (t);
> + }
> }
>
> /* If we're using __cxa_atexit, register a function that calls the
> --- gcc/testsuite/g++.dg/opt/init3.C.jj 2021-11-03 17:53:01.872472570
> +0100
> +++ gcc/testsuite/g++.dg/opt/init3.C 2021-11-03 17:52:57.484535115 +0100
> @@ -0,0 +1,31 @@
> +// PR c++/102876
> +// { dg-do compile }
> +// { dg-options "-O2 -fdump-tree-dyninit" }
> +// { dg-final { scan-tree-dump "dynamic initialization of b\[\n\r]*
> optimized into: 1" "dyninit" } }
> +// { dg-final { scan-tree-dump "dynamic initialization of e\[\n\r]*
> optimized into: {.e=5, .f={.a=1, .b=2, .c=3, .d=6}, .g=6}\[\n\r]* and making
> it read-only" "dyninit" } }
> +// { dg-final { scan-tree-dump "dynamic initialization of f\[\n\r]*
> optimized into: {.e=7, .f={.a=1, .b=2, .c=3, .d=6}, .g=1}" "dyninit" } }
> +// { dg-final { scan-tree-dump "dynamic initialization of h\[\n\r]*
> optimized into: {.h=8, .i={.a=1, .b=2, .c=3, .d=6}, .j=9}" "dyninit" } }
> +// { dg-final { scan-tree-dump-times "dynamic initialization of " 4
> "dyninit" } }
> +// { dg-final { scan-tree-dump-times "and making it read-only" 1 "dyninit" }
> }
> +
> +struct S { S () : a(1), b(2), c(3), d(4) { d += 2; } int a, b, c, d; };
> +struct T { int e; S f; int g; };
> +struct U { int h; mutable S i; int j; };
> +extern int b;
> +int foo (int &);
> +int bar (int &);
> +int baz () { return 1; }
> +int qux () { return b = 2; }
> +// Dynamic initialization of a shouldn't be optimized, foo can't be inlined.
> +int a = foo (b);
> +int b = baz ();
> +// Likewise for c.
> +int c = bar (b);
> +// While qux is inlined, the dynamic initialization modifies another
> +// variable, so punt for d as well.
> +int d = qux ();
> +const T e = { 5, S (), 6 };
> +T f = { 7, S (), baz () };
> +const T &g = e;
> +const U h = { 8, S (), 9 };
> +const U &i = h;
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
