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[NFC] Skip parsing instructions in first parser pass #8601

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Merged
tlively merged 4 commits into from
Apr 15, 2026
+48 −11
Merged

[NFC] Skip parsing instructions in first parser pass #8601

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a6e1e9a
[NFC] Simplify lexer and move to header
tlively Apr 13, 2026
b2528ad
fixes
tlively Apr 14, 2026
6c3f3c9
[NFC] Skip parsing instructions in first parser pass
tlively Apr 8, 2026
d1562f5
Merge branch 'main' into parser-fastscan
tlively Apr 14, 2026
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33 changes: 33 additions & 0 deletions src/parser/context-decls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
*/

#include "contexts.h"
#include "parsers.h"

namespace wasm::WATParser {

Expand Down Expand Up @@ -302,4 +303,36 @@ Result<> ParseDeclsCtx::addTag(Name name,
return Ok{};
}

bool ParseDeclsCtx::skipFunctionBody() {
using namespace std::string_view_literals;
size_t depth = 1;
while (depth > 0 && !in.empty()) {
if (in.takeLParen()) {
++depth;
continue;
}
if (in.takeRParen()) {
--depth;
continue;
}
if (auto kw = in.takeKeyword()) {
if (*kw == "block"sv || *kw == "loop"sv || *kw == "if"sv ||
*kw == "try"sv || *kw == "try_table"sv) {
in.takeID();
(void)typeuse(*this);
continue;
}
if (*kw == "call_indirect"sv || *kw == "return_call_indirect"sv) {
(void)maybeTableidx(*this);
(void)typeuse(*this, false);
continue;
}
continue;
}
in.take(1);
in.advance();
}
return true;
}

} // namespace wasm::WATParser
2 changes: 2 additions & 0 deletions src/parser/contexts.h
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Expand Up @@ -1074,6 +1074,8 @@ struct ParseDeclsCtx : NullTypeParserCtx, NullInstrParserCtx {
recTypeDefs.push_back({{}, pos, Index(recTypeDefs.size()), {}});
}

bool skipFunctionBody();

Limits makeLimits(uint64_t n, std::optional<uint64_t> m) {
return Limits{n, m};
}
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18 changes: 9 additions & 9 deletions src/parser/lexer.h
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Expand Up @@ -82,6 +82,15 @@ struct Lexer {
advance();
}

// Consume the next `n` characters.
void take(size_t n) { pos += n; }
void takeAll() { pos = buffer.size(); }

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@MaxGraey MaxGraey Apr 14, 2026 •
edited
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Minor proposal for API:

template<typename F>
inline void takeWhile(F&& pred, size_t n = 1) {
  while (pred()) {
    pos += n;
  }
}

template<typename F>
inline void takeUntil(F&& pred, size_t n = 1) {
  while (!pred()) {
    pos += n;
  }
}

This may simplify some code like this into

takeWhile(idchar);

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@tlively tlively Apr 14, 2026

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I think there are few enough places where this pattern would apply and they are already simple enough that we probably don't need this abstraction right now. But it's a good idea to keep in mind if we parser more repetitive patterns in the future.

// Whether the unlexed input starts with prefix `sv`.
size_t startsWith(std::string_view sv) const {
return next().starts_with(sv);
}

std::optional<char> peekChar() const;

bool peekLParen() { return !empty() && peek() == '('; }
Expand Down Expand Up @@ -155,15 +164,6 @@ struct Lexer {
}

private:
// Whether the unlexed input starts with prefix `sv`.
size_t startsWith(std::string_view sv) const {
return next().starts_with(sv);
}

// Consume the next `n` characters.
void take(size_t n) { pos += n; }
void takeAll() { pos = buffer.size(); }

std::optional<int> getDigit(char c);

std::optional<int> getHexDigit(char c);
Expand Down
6 changes: 4 additions & 2 deletions src/parser/parsers.h
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Expand Up @@ -3491,6 +3491,7 @@ template<typename Ctx> MaybeResult<> func(Ctx& ctx) {
typename Ctx::TypeUseT type;
Exactness exact = Exact;
std::optional<typename Ctx::LocalsT> localVars;
bool skipped = false;

if (import) {
auto use = exacttypeuse(ctx);
Expand All @@ -3505,13 +3506,14 @@ template<typename Ctx> MaybeResult<> func(Ctx& ctx) {
CHECK_ERR(l);
localVars = *l;
}
if (!ctx.skipFunctionBody()) {
skipped = ctx.skipFunctionBody();
if (!skipped) {
CHECK_ERR(instrs(ctx));
ctx.setSrcLoc(ctx.in.takeAnnotations());
}
}

if (!ctx.skipFunctionBody() && !ctx.in.takeRParen()) {
if ((import || !skipped) && !ctx.in.takeRParen()) {
return ctx.in.err("expected end of function");
}

Expand Down
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