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mruby-compiler: optimize case statement bytecode with JMPNOT instruction

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Replace JMPIF+JMP pattern with JMPNOT for last condition in each when
clause, allowing when bodies to execute inline. Also eliminate no-op
JMP instructions from else clauses, reducing overall instruction count.

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-09-06 08:45:55 +09:00
parent a4754c03b0
commit 300557d6ee
1 changed files with 50 additions and 20 deletions
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mrbgems/mruby-compiler/core/codegen.c
+50 -20
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@@ -4948,7 +4948,8 @@ gen_case_var(codegen_scope *s, node *varnode, int val)
struct mrb_ast_node **when_clauses = CASE_NODE_WHENS(case_n);
int head = 0;
uint32_t pos1, pos2, pos3, tmp;
uint32_t pos3, tmp;
uint32_t next_when_pos = JMPLINK_START;
node *n;
pos3 = JMPLINK_START;
@@ -4959,18 +4960,25 @@ gen_case_var(codegen_scope *s, node *varnode, int val)
codegen(s, value, VAL);
}
/* Iterate through when clauses array (replacing cons-list traversal) */
/* Iterate through when clauses array with JMPNOT optimization */
for (int i = 0; i < when_count; i++) {
node *when_clause = (node*)when_clauses[i];
if (!when_clause) continue;
/* Dispatch previous when's "next" jump to this location */
if (next_when_pos != JMPLINK_START) {
dispatch_linked(s, next_when_pos);
next_when_pos = JMPLINK_START;
}
/* when_clause is (condition . body) cons node */
node *args = when_clause->car; /* when conditions */
node *body = when_clause->cdr; /* when body */
/* Process when conditions - original logic unchanged */
/* Process when conditions with JMPNOT optimization */
n = args;
pos1 = pos2 = JMPLINK_START;
uint32_t condition_success_pos = JMPLINK_START;
while (n) {
codegen(s, n->car, VAL);
if (head) {
@@ -4986,40 +4994,62 @@ gen_case_var(codegen_scope *s, node *varnode, int val)
else {
pop();
}
tmp = genjmp2(s, OP_JMPIF, cursp(), pos2, !head);
pos2 = tmp;
if (n->cdr) {
/* More conditions in this when - use JMPIF to success handler */
tmp = genjmp2(s, OP_JMPIF, cursp(), condition_success_pos, !head);
condition_success_pos = tmp;
}
else {
/* Last condition - use JMPNOT to next when clause */
tmp = genjmp2(s, OP_JMPNOT, cursp(), next_when_pos, !head);
next_when_pos = tmp;
}
n = n->cdr;
}
if (args) {
pos1 = genjmp_0(s, OP_JMP);
dispatch_linked(s, pos2);
/* Dispatch multiple condition success jumps to body */
if (condition_success_pos != JMPLINK_START) {
dispatch_linked(s, condition_success_pos);
}
/* Generate when body - original logic unchanged */
/* Generate when body inline - no extra JMP needed! */
codegen(s, body, val);
if (val) pop();
tmp = genjmp(s, OP_JMP, pos3);
pos3 = tmp;
dispatch(s, pos1);
}
/* Handle else clause like the original - before the final result logic */
/* Dispatch final "next when" jump to else clause or nil handling */
if (next_when_pos != JMPLINK_START) {
dispatch_linked(s, next_when_pos);
}
/* Handle else clause - DON'T generate unnecessary JMP */
if (else_body) {
codegen(s, else_body, val);
if (val) pop();
tmp = genjmp(s, OP_JMP, pos3);
pos3 = tmp;
/* Only generate JMP if there will be more code after this (i.e., LOADNIL case) */
if (!val || !else_body) {
tmp = genjmp(s, OP_JMP, pos3);
pos3 = tmp;
}
}
/* Apply original's "nil-first, align-last" strategy for VAL case */
if (val) {
uint32_t pos = cursp();
genop_1(s, OP_LOADNIL, cursp());
if (pos3 != JMPLINK_START) dispatch_linked(s, pos3);
if (head) pop();
if (cursp() != pos) {
gen_move(s, cursp(), pos, 0);
if (!else_body) {
/* Only generate LOADNIL if there's no else clause */
genop_1(s, OP_LOADNIL, cursp());
}
/* Always dispatch pos3 jumps */
if (pos3 != JMPLINK_START) dispatch_linked(s, pos3);
if (head) {
/* This is the crucial MOVE instruction! Move result to original case value position */
gen_move(s, head, cursp(), 0);
pop();
}
/* Always push to maintain stack alignment */
push();
}
else {