Render switch discriminant once per group; drop dead inner scope#253
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This was referenced May 20, 2026
robrussell
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May 20, 2026
The optimized Ok() switch-block code in _generate_optimized_ok_method_body
was rendering each switch group's discriminant twice: once unscoped at
grouping time to build the SWITCH: key, and again with the active
ExpressionScope at emit time. Render it once with the scope and reuse
the result. The result is stable for equivalent discriminants because
ExpressionScope.add dedupes by inner rendered form, so it still works
as a grouping key.
The ok_method_switch_block template's \${inner_scope_definitions}
placeholder was unused — the inner ExpressionScope it referenced had
nothing added to it. Removed both, which also drops the blank line
each switch block carried in the goldens.
No behavioral change; purely compile-time cleanup. Golden churn
limited to the blank-line removal in four files (one line per existing
switch block).
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Three composing changes to the optimized Ok() switch generator:
1. Case-label sort. Each switch arm's labels are sorted by the
underlying integer/enum value before emit. _case_sort_key()
returns the int for sorting. Sorted cases give older embedded
GCCs (the ones shipped with microblaze-elf and many bare-metal
arm-none-eabi toolchains) a better shot at emitting a dense
jump table rather than an if-ladder.
2. Identical-body coalescing. Cases whose rendered body text is
identical (same field set in the same order) are merged into a
single arm with multiple \`case X:\` labels. The C++ compiler
emits one body for the whole arm — a real text-size win once a
later PR (disjunction matching) starts producing such pairs.
3. Multi-field per case. When two conditional fields share a
discriminant + case value (\`if tag == 0: a\` and \`if tag == 0: b\`),
they're now bundled into the same case arm rather than the second
falling back to a separate if-statement. Each field's validation
becomes one line of the case body.
The ok_method_switch_case template becomes ok_method_switch_arm,
taking pre-formatted \${case_labels} and \${case_body} strings.
Single-label single-field arms render identically to the old
template, so golden churn is limited to the f0_copy field in
testdata/many_conditionals.emb folding into case 0 of the
LargeConditionals switch.
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The optimized
Ok()switch-block code in_generate_optimized_ok_method_bodywas rendering each switch group's discriminant twice — once unscoped at grouping time to build the SWITCH key, and again with the activeExpressionScopeat emit time. Render it once with the scope and reuse the result. BecauseExpressionScope.adddedupes by inner rendered form, the result is stable for equivalent discriminants and still works as a grouping key.The
ok_method_switch_blocktemplate's${inner_scope_definitions}placeholder was unused — the innerExpressionScopeit referenced had nothing added to it. Removed both, which also drops the blank line each switch block was carrying in the goldens.Pure compile-time cleanup; no behavioral change.
Size impact
Foundation for #254 / #256 / #257 / #258 / #259 (see those for the wins this enables).