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bpo-39151: Simplify DFS in the assembler (GH-17733)

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Pablo Galindo 2020-06-28 01:55:47 +01:00 committed by GitHub
parent 9d197c7d48
commit 60eb9f1ab5
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 18 additions and 33 deletions
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51
Python/compile.c
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@ -67,8 +67,6 @@ typedef struct basicblock_ {
/* If b_next is non-NULL, it is a pointer to the next /* If b_next is non-NULL, it is a pointer to the next
block reached by normal control flow. */ block reached by normal control flow. */
struct basicblock_ *b_next; struct basicblock_ *b_next;
/* b_seen is used to perform a DFS of basicblocks. */
unsigned b_seen : 1;
/* b_return is true if a RETURN_VALUE opcode is inserted. */ /* b_return is true if a RETURN_VALUE opcode is inserted. */
unsigned b_return : 1; unsigned b_return : 1;
/* depth of stack upon entry of block, computed by stackdepth() */ /* depth of stack upon entry of block, computed by stackdepth() */
@ -5413,7 +5411,7 @@ struct assembler {
PyObject *a_bytecode; /* string containing bytecode */ PyObject *a_bytecode; /* string containing bytecode */
int a_offset; /* offset into bytecode */ int a_offset; /* offset into bytecode */
int a_nblocks; /* number of reachable blocks */ int a_nblocks; /* number of reachable blocks */
basicblock **a_postorder; /* list of blocks in dfs postorder */ basicblock **a_reverse_postorder; /* list of blocks in dfs postorder */
PyObject *a_lnotab; /* string containing lnotab */ PyObject *a_lnotab; /* string containing lnotab */
int a_lnotab_off; /* offset into lnotab */ int a_lnotab_off; /* offset into lnotab */
int a_lineno; /* last lineno of emitted instruction */ int a_lineno; /* last lineno of emitted instruction */
@ -5423,26 +5421,14 @@ struct assembler {
static void static void
dfs(struct compiler *c, basicblock *b, struct assembler *a, int end) dfs(struct compiler *c, basicblock *b, struct assembler *a, int end)
{ {
int i, j;
/* Get rid of recursion for normal control flow. /* There is no real depth-first-search to do here because all the
Since the number of blocks is limited, unused space in a_postorder * blocks are emitted in topological order already, so we just need to
(from a_nblocks to end) can be used as a stack for still not ordered * follow the b_next pointers and place them in a->a_reverse_postorder in
blocks. */ * reverse order and make sure that the first one starts at 0. */
for (j = end; b && !b->b_seen; b = b->b_next) {
b->b_seen = 1; for (a->a_nblocks = 0; b != NULL; b = b->b_next) {
assert(a->a_nblocks < j); a->a_reverse_postorder[a->a_nblocks++] = b;
a->a_postorder[--j] = b;
}
while (j < end) {
b = a->a_postorder[j++];
for (i = 0; i < b->b_iused; i++) {
struct instr *instr = &b->b_instr[i];
if (instr->i_jrel || instr->i_jabs)
dfs(c, instr->i_target, a, j);
}
assert(a->a_nblocks < j);
a->a_postorder[a->a_nblocks++] = b;
} }
} }
@ -5543,9 +5529,9 @@ assemble_init(struct assembler *a, int nblocks, int firstlineno)
PyErr_NoMemory(); PyErr_NoMemory();
return 0; return 0;
} }
a->a_postorder = (basicblock **)PyObject_Malloc( a->a_reverse_postorder = (basicblock **)PyObject_Malloc(
sizeof(basicblock *) * nblocks); sizeof(basicblock *) * nblocks);
if (!a->a_postorder) { if (!a->a_reverse_postorder) {
PyErr_NoMemory(); PyErr_NoMemory();
return 0; return 0;
} }
@ -5557,8 +5543,8 @@ assemble_free(struct assembler *a)
{ {
Py_XDECREF(a->a_bytecode); Py_XDECREF(a->a_bytecode);
Py_XDECREF(a->a_lnotab); Py_XDECREF(a->a_lnotab);
if (a->a_postorder) if (a->a_reverse_postorder)
PyObject_Free(a->a_postorder); PyObject_Free(a->a_reverse_postorder);
} }
static int static int
@ -5719,8 +5705,8 @@ assemble_jump_offsets(struct assembler *a, struct compiler *c)
Replace block pointer with position in bytecode. */ Replace block pointer with position in bytecode. */
do { do {
totsize = 0; totsize = 0;
for (i = a->a_nblocks - 1; i >= 0; i--) { for (i = 0; i < a->a_nblocks; i++) {
b = a->a_postorder[i]; b = a->a_reverse_postorder[i];
bsize = blocksize(b); bsize = blocksize(b);
b->b_offset = totsize; b->b_offset = totsize;
totsize += bsize; totsize += bsize;
@ -5975,10 +5961,9 @@ dump_instr(const struct instr *i)
static void static void
dump_basicblock(const basicblock *b) dump_basicblock(const basicblock *b)
{ {
const char *seen = b->b_seen ? "seen " : "";
const char *b_return = b->b_return ? "return " : ""; const char *b_return = b->b_return ? "return " : "";
fprintf(stderr, "used: %d, depth: %d, offset: %d %s%s\n", fprintf(stderr, "used: %d, depth: %d, offset: %d %s\n",
b->b_iused, b->b_startdepth, b->b_offset, seen, b_return); b->b_iused, b->b_startdepth, b->b_offset, b_return);
if (b->b_instr) { if (b->b_instr) {
int i; int i;
for (i = 0; i < b->b_iused; i++) { for (i = 0; i < b->b_iused; i++) {
@ -6030,8 +6015,8 @@ assemble(struct compiler *c, int addNone)
assemble_jump_offsets(&a, c); assemble_jump_offsets(&a, c);
/* Emit code in reverse postorder from dfs. */ /* Emit code in reverse postorder from dfs. */
for (i = a.a_nblocks - 1; i >= 0; i--) { for (i = 0; i < a.a_nblocks; i++) {
b = a.a_postorder[i]; b = a.a_reverse_postorder[i];
for (j = 0; j < b->b_iused; j++) for (j = 0; j < b->b_iused; j++)
if (!assemble_emit(&a, &b->b_instr[j])) if (!assemble_emit(&a, &b->b_instr[j]))
goto error; goto error;