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| author | Damien George <damien.p.george@gmail.com> | 2014-12-12 17:19:56 +0000 |
|---|---|---|
| committer | Damien George <damien.p.george@gmail.com> | 2014-12-12 17:19:56 +0000 |
| commit | e181c0dc07c32408d7584ef5b078cd3e88076d3f (patch) | |
| tree | 626f340b4c82a0336cc3e4e73431deb051189a06 /py | |
| parent | 7764f163fa54dc39532f7729c774ab92611bb115 (diff) | |
| download | micropython-e181c0dc07c32408d7584ef5b078cd3e88076d3f.tar.gz micropython-e181c0dc07c32408d7584ef5b078cd3e88076d3f.zip | |
py: Fix optimised for-loop compiler so it follows proper semantics.
You can now assign to the range end variable and the for-loop still
works correctly. This fully addresses issue #565.
Also fixed a bug with the stack not being fully popped when breaking out
of an optimised for-loop (and it's actually impossible to write a test
for this case!).
Diffstat (limited to 'py')
| -rw-r--r-- | py/compile.c | 54 |
1 files changed, 39 insertions, 15 deletions
diff --git a/py/compile.c b/py/compile.c index dfc3e01af5..9e529443e6 100644 --- a/py/compile.c +++ b/py/compile.c @@ -1776,26 +1776,40 @@ STATIC void compile_while_stmt(compiler_t *comp, mp_parse_node_struct_t *pns) { } #if !MICROPY_EMIT_CPYTHON -// TODO preload end and step onto stack if they are not constants -// 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 +// This function compiles an optimised for-loop of the form: +// for <var> in range(<start>, <end>, <step>): +// <body> +// else: +// <else> +// <var> must be an identifier and <step> must be a small-int. +// +// Semantics of for-loop require: +// - final failing value should not be stored in the loop variable +// - if the loop never runs, the loop variable should never be assigned +// - assignments to <var>, <end> or <step> in the body do not alter the loop +// (<step> is a constant for us, so no need to worry about it changing) +// +// If <end> is a small-int, then the stack during the for-loop contains just +// the current value of <var>. Otherwise, the stack contains <end> then the +// current value of <var>. STATIC 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 - // note that we don't need to pop anything when breaking from an optimise for loop uint top_label = comp_next_label(comp); uint entry_label = comp_next_label(comp); - // compile: start, duplicated on stack + // put the end value on the stack if it's not a small-int constant + bool end_on_stack = !MP_PARSE_NODE_IS_SMALL_INT(pn_end); + if (end_on_stack) { + compile_node(comp, pn_end); + } + + // compile: start compile_node(comp, pn_start); - 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(adjust_stack_size, -1); - // duplicate next value and store it to var EMIT(dup_top); c_assign(comp, pn_var, ASSIGN_STORE); @@ -1805,15 +1819,20 @@ STATIC void compile_for_stmt_optimised_range(compiler_t *comp, mp_parse_node_t p EMIT_ARG(label_assign, continue_label); - // compile: var + step, duplicated on stack + // compile: var + step compile_node(comp, pn_step); EMIT_ARG(binary_op, MP_BINARY_OP_INPLACE_ADD); - EMIT(dup_top); EMIT_ARG(label_assign, entry_label); // compile: if var <cond> end: goto top - compile_node(comp, pn_end); + if (end_on_stack) { + EMIT(dup_top_two); + EMIT(rot_two); + } else { + EMIT(dup_top); + compile_node(comp, pn_end); + } assert(MP_PARSE_NODE_IS_SMALL_INT(pn_step)); if (MP_PARSE_NODE_LEAF_SMALL_INT(pn_step) >= 0) { EMIT_ARG(binary_op, MP_BINARY_OP_LESS); @@ -1822,15 +1841,20 @@ STATIC void compile_for_stmt_optimised_range(compiler_t *comp, mp_parse_node_t p } 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 compile_node(comp, pn_else); EMIT_ARG(label_assign, break_label); + + // discard final value of var that failed the loop condition + EMIT(pop_top); + + // discard <end> value if it's on the stack + if (end_on_stack) { + EMIT(pop_top); + } } #endif |