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py: Fix bug in optimised for .. range.

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Don't store final, failing value to the loop variable.  This fix also
makes for .. range a bit more efficient, as it uses less store/load
pairs for the loop variable.
This commit is contained in:
Damien George
2014-03-31 18:02:22 +01:00
parent 8cd72bdf92
commit 3ff2d03891
3 changed files with 183 additions and 7 deletions
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23
py/compile.c
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@@ -1534,35 +1534,41 @@ void compile_while_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) {
}
// TODO preload end and step onto stack if they are not constants
// TODO check if step is negative and do opposite test
// Note that, as per semantics of for .. range, the final failing value should not be stored in the loop variable
// And, if the loop never runs, the loop variable should never be assigned
void compile_for_stmt_optimised_range(compiler_t *comp, mp_parse_node_t pn_var, mp_parse_node_t pn_start, mp_parse_node_t pn_end, mp_parse_node_t pn_step, mp_parse_node_t pn_body, mp_parse_node_t pn_else) {
START_BREAK_CONTINUE_BLOCK
int top_label = comp_next_label(comp);
int entry_label = comp_next_label(comp);
// compile: var = start
// compile: start, duplicated on stack
compile_node(comp, pn_start);
c_assign(comp, pn_var, ASSIGN_STORE);
EMIT(dup_top);
EMIT_ARG(jump, entry_label);
EMIT_ARG(label_assign, top_label);
// at this point we actually have 1 less element on the stack
EMIT_ARG(set_stack_size, EMIT(get_stack_size) - 1);
// store next value to var
c_assign(comp, pn_var, ASSIGN_STORE);
// compile body
compile_node(comp, pn_body);
EMIT_ARG(label_assign, continue_label);
// compile: var += step
c_assign(comp, pn_var, ASSIGN_AUG_LOAD);
// compile: var + step, duplicated on stack
compile_node(comp, pn_var);
compile_node(comp, pn_step);
EMIT_ARG(binary_op, MP_BINARY_OP_INPLACE_ADD);
c_assign(comp, pn_var, ASSIGN_AUG_STORE);
EMIT(dup_top);
EMIT_ARG(label_assign, entry_label);
// compile: if var <cond> end: goto top
compile_node(comp, pn_var);
compile_node(comp, pn_end);
assert(MP_PARSE_NODE_IS_SMALL_INT(pn_step));
if (MP_PARSE_NODE_LEAF_SMALL_INT(pn_step) >= 0) {
@@ -1572,6 +1578,9 @@ void compile_for_stmt_optimised_range(compiler_t *comp, mp_parse_node_t pn_var,
}
EMIT_ARG(pop_jump_if_true, top_label);
// discard final value of var that failed the loop condition
EMIT(pop_top);
// break/continue apply to outer loop (if any) in the else block
END_BREAK_CONTINUE_BLOCK