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bpo-42246: Eliminate jumps to exit blocks by copying those blocks. (#23251)
* Compiler: eliminate jumps to short exit blocks by copying.
This commit is contained in:
Mark Shannon
GitHub
parent
750c5abf43
commit
cc75ab791d
6 changed files with 4662 additions and 4664 deletions
163
Python/compile.c
163
Python/compile.c
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@ -96,6 +96,10 @@ typedef struct basicblock_ {
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/* b_return is true if a RETURN_VALUE opcode is inserted. */
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unsigned b_return : 1;
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unsigned b_reachable : 1;
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/* Basic block has no fall through (it ends with a return, raise or jump) */
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unsigned b_nofallthrough : 1;
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/* Basic block exits scope (it ends with a return or raise) */
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unsigned b_exit : 1;
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/* depth of stack upon entry of block, computed by stackdepth() */
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int b_startdepth;
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/* instruction offset for block, computed by assemble_jump_offsets() */
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@ -5434,28 +5438,14 @@ struct assembler {
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PyObject *a_bytecode; /* string containing bytecode */
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int a_offset; /* offset into bytecode */
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int a_nblocks; /* number of reachable blocks */
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basicblock **a_reverse_postorder; /* list of blocks in dfs postorder */
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PyObject *a_lnotab; /* string containing lnotab */
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int a_lnotab_off; /* offset into lnotab */
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int a_prevlineno; /* lineno of last emitted line in line table */
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int a_lineno; /* lineno of last emitted instruction */
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int a_lineno_start; /* bytecode start offset of current lineno */
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basicblock *a_entry;
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};
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static void
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dfs(struct compiler *c, basicblock *b, struct assembler *a, int end)
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{
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/* There is no real depth-first-search to do here because all the
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* blocks are emitted in topological order already, so we just need to
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* follow the b_next pointers and place them in a->a_reverse_postorder in
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* reverse order and make sure that the first one starts at 0. */
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for (a->a_nblocks = 0; b != NULL; b = b->b_next) {
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a->a_reverse_postorder[a->a_nblocks++] = b;
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}
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}
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Py_LOCAL_INLINE(void)
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stackdepth_push(basicblock ***sp, basicblock *b, int depth)
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{
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@ -5553,12 +5543,7 @@ assemble_init(struct assembler *a, int nblocks, int firstlineno)
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PyErr_NoMemory();
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return 0;
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}
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a->a_reverse_postorder = (basicblock **)PyObject_Malloc(
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sizeof(basicblock *) * nblocks);
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if (!a->a_reverse_postorder) {
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PyErr_NoMemory();
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return 0;
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}
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return 1;
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}
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@ -5567,8 +5552,6 @@ assemble_free(struct assembler *a)
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{
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Py_XDECREF(a->a_bytecode);
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Py_XDECREF(a->a_lnotab);
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if (a->a_reverse_postorder)
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PyObject_Free(a->a_reverse_postorder);
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}
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static int
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@ -5697,8 +5680,7 @@ assemble_jump_offsets(struct assembler *a, struct compiler *c)
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Replace block pointer with position in bytecode. */
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do {
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totsize = 0;
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for (i = 0; i < a->a_nblocks; i++) {
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b = a->a_reverse_postorder[i];
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for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
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bsize = blocksize(b);
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b->b_offset = totsize;
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totsize += bsize;
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@ -5966,7 +5948,7 @@ assemble(struct compiler *c, int addNone)
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{
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basicblock *b, *entryblock;
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struct assembler a;
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int i, j, nblocks;
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int j, nblocks;
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PyCodeObject *co = NULL;
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PyObject *consts = NULL;
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@ -5997,7 +5979,8 @@ assemble(struct compiler *c, int addNone)
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}
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if (!assemble_init(&a, nblocks, c->u->u_firstlineno))
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goto error;
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dfs(c, entryblock, &a, nblocks);
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a.a_entry = entryblock;
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a.a_nblocks = nblocks;
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consts = consts_dict_keys_inorder(c->u->u_consts);
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if (consts == NULL) {
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@ -6010,9 +5993,8 @@ assemble(struct compiler *c, int addNone)
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/* Can't modify the bytecode after computing jump offsets. */
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assemble_jump_offsets(&a, c);
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/* Emit code in reverse postorder from dfs. */
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for (i = 0; i < a.a_nblocks; i++) {
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b = a.a_reverse_postorder[i];
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/* Emit code. */
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for(b = entryblock; b != NULL; b = b->b_next) {
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for (j = 0; j < b->b_iused; j++)
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if (!assemble_emit(&a, &b->b_instr[j]))
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goto error;
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@ -6097,6 +6079,8 @@ fold_tuple_on_constants(struct instr *inst,
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return 0;
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}
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/* Maximum size of basic block that should be copied in optimizer */
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#define MAX_COPY_SIZE 4
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/* Optimization */
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static int
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@ -6238,19 +6222,29 @@ optimize_basic_block(basicblock *bb, PyObject *consts)
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case JUMP_ABSOLUTE:
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case JUMP_FORWARD:
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assert (i == bb->b_iused-1);
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switch(target->i_opcode) {
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case JUMP_FORWARD:
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inst->i_target = target->i_target;
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break;
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case JUMP_ABSOLUTE:
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case RETURN_VALUE:
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case RERAISE:
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case RAISE_VARARGS:
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lineno = inst->i_lineno;
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*inst = *target;
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inst->i_lineno = lineno;
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break;
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}
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if (inst->i_target->b_exit && inst->i_target->b_iused <= MAX_COPY_SIZE) {
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basicblock *to_copy = inst->i_target;
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*inst = to_copy->b_instr[0];
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for (i = 1; i < to_copy->b_iused; i++) {
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int index = compiler_next_instr(bb);
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if (index < 0) {
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return -1;
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}
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bb->b_instr[index] = to_copy->b_instr[i];
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}
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bb->b_exit = 1;
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}
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break;
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}
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}
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@ -6262,52 +6256,63 @@ error:
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static void
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clean_basic_block(basicblock *bb) {
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/* Remove NOPs and any code following a return or re-raise. */
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/* Remove NOPs. */
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int dest = 0;
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int prev_lineno = -1;
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for (int src = 0; src < bb->b_iused; src++) {
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int lineno = bb->b_instr[src].i_lineno;
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switch(bb->b_instr[src].i_opcode) {
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case RETURN_VALUE:
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case RERAISE:
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bb->b_next = NULL;
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bb->b_instr[dest] = bb->b_instr[src];
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dest++;
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goto end;
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case NOP:
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{
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/* Eliminate no-op if it doesn't have a line number, or
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* if the next instruction has same line number or no line number, or
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* if the previous instruction had the same line number. */
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if (lineno < 0) {
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break;
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}
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if (prev_lineno == lineno) {
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break;
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}
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if (src < bb->b_iused - 1) {
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int next_lineno = bb->b_instr[src+1].i_lineno;
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if (next_lineno < 0 || next_lineno == lineno) {
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bb->b_instr[src+1].i_lineno = lineno;
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break;
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}
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if (bb->b_instr[src].i_opcode == NOP) {
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/* Eliminate no-op if it doesn't have a line number, or
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* if the next instruction has same line number or no line number, or
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* if the previous instruction had the same line number. */
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if (lineno < 0) {
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continue;
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}
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if (prev_lineno == lineno) {
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continue;
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}
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if (src < bb->b_iused - 1) {
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int next_lineno = bb->b_instr[src+1].i_lineno;
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if (next_lineno < 0 || next_lineno == lineno) {
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bb->b_instr[src+1].i_lineno = lineno;
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continue;
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}
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}
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/* fallthrough */
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default:
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if (dest != src) {
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bb->b_instr[dest] = bb->b_instr[src];
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}
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dest++;
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prev_lineno = lineno;
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break;
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}
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if (dest != src) {
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bb->b_instr[dest] = bb->b_instr[src];
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}
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dest++;
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prev_lineno = lineno;
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}
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end:
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assert(dest <= bb->b_iused);
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bb->b_iused = dest;
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}
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static void
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normalise_basic_block(basicblock *bb) {
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/* Remove any code following a return or re-raise,
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and mark those blocks as exit and/or nofallthrough. */
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for (int i = 0; i < bb->b_iused; i++) {
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switch(bb->b_instr[i].i_opcode) {
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case RETURN_VALUE:
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case RAISE_VARARGS:
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case RERAISE:
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bb->b_iused = i+1;
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bb->b_exit = 1;
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bb->b_nofallthrough = 1;
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return;
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case JUMP_ABSOLUTE:
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case JUMP_FORWARD:
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bb->b_iused = i+1;
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bb->b_nofallthrough = 1;
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return;
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}
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}
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}
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static int
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mark_reachable(struct assembler *a) {
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basicblock **stack, **sp;
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@ -6315,12 +6320,11 @@ mark_reachable(struct assembler *a) {
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if (stack == NULL) {
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return -1;
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}
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basicblock *entry = a->a_reverse_postorder[0];
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entry->b_reachable = 1;
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*sp++ = entry;
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a->a_entry->b_reachable = 1;
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*sp++ = a->a_entry;
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while (sp > stack) {
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basicblock *b = *(--sp);
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if (b->b_next && b->b_next->b_reachable == 0) {
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if (b->b_next && !b->b_nofallthrough && b->b_next->b_reachable == 0) {
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b->b_next->b_reachable = 1;
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*sp++ = b->b_next;
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}
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@ -6352,20 +6356,23 @@ mark_reachable(struct assembler *a) {
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static int
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optimize_cfg(struct assembler *a, PyObject *consts)
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{
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for (int i = 0; i < a->a_nblocks; i++) {
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if (optimize_basic_block(a->a_reverse_postorder[i], consts)) {
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for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
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normalise_basic_block(b);
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}
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for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
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if (optimize_basic_block(b, consts)) {
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return -1;
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}
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clean_basic_block(a->a_reverse_postorder[i]);
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assert(a->a_reverse_postorder[i]->b_reachable == 0);
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clean_basic_block(b);
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assert(b->b_reachable == 0);
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}
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if (mark_reachable(a)) {
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return -1;
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}
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/* Delete unreachable instructions */
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for (int i = 0; i < a->a_nblocks; i++) {
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if (a->a_reverse_postorder[i]->b_reachable == 0) {
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a->a_reverse_postorder[i]->b_iused = 0;
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for (basicblock *b = a->a_entry; b != NULL; b = b->b_next) {
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if (b->b_reachable == 0) {
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b->b_iused = 0;
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}
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}
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return 0;
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