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Revert "[wasm][debug] Cache debugging code"

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This reverts commit fab754ff56.

Reason for revert: TSan failures: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN%20-%20isolates/13875/overview

Original change's description:
> [wasm][debug] Cache debugging code
>
> This adds a little cache for debugging code, including stepping code.
> Especially in stepping, we are currently repeatedly recompiling the same
> function, because whenever we pause (after every step) we clear
> stepping, only to reinstantiate it if the user continues stepping.
> Especially in source-level stepping this is wasteful, because stepping
> over a single line of C++ code can execute hundreds or thousands of
> steps in wasm.
>
> R=​thibaudm@chromium.org
>
> Bug: chromium:1172299
> Change-Id: Id59a26cc67a5bf4a2d3cf6b1e8f14a8b1c73712c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2732015
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73162}

Bug: chromium:1172299
Change-Id: I8fac7701e6f58012c8e17322c22f29692ee8932b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2732020
Auto-Submit: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#73168}
This commit is contained in:
Clemens Backes 2021-03-03 17:35:00 +00:00 committed by Commit Bot
parent 7d69193fb2
commit 685f25964a
1 changed files with 0 additions and 42 deletions
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42
src/wasm/wasm-debug.cc
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@ -219,20 +219,6 @@ class DebugInfoImpl {
Vector<const int> offsets,
int dead_breakpoint) {
DCHECK(!mutex_.TryLock()); // Mutex is held externally.
// Check the cache first.
for (auto begin = cached_debugging_code_.begin(), it = begin,
end = cached_debugging_code_.end();
it != end; ++it) {
if (it->func_index == func_index &&
it->breakpoint_offsets.as_vector() == offsets &&
it->dead_breakpoint == dead_breakpoint) {
// Rotate the cache entry to the front (for LRU).
for (; it != begin; --it) std::iter_swap(it, it - 1);
return it->code;
}
}
// Recompile the function with Liftoff, setting the new breakpoints.
// Not thread-safe. The caller is responsible for locking {mutex_}.
CompilationEnv env = native_module_->CreateCompilationEnv();
@ -269,21 +255,6 @@ class DebugInfoImpl {
debug_side_tables_.emplace(new_code, std::move(debug_sidetable));
}
// Insert new code into the cache. Insert before existing elements for LRU.
cached_debugging_code_.insert(
cached_debugging_code_.begin(),
CachedDebuggingCode{func_index, OwnedVector<int>::Of(offsets),
dead_breakpoint, new_code});
// Increase the ref count (for the cache entry).
new_code->IncRef();
// Remove exceeding element.
if (cached_debugging_code_.size() > kMaxCachedDebuggingCode) {
WasmCode::DecrementRefCount(
VectorOf({cached_debugging_code_.back().code}));
cached_debugging_code_.pop_back();
}
DCHECK_GE(kMaxCachedDebuggingCode, cached_debugging_code_.size());
return new_code;
}
@ -678,19 +649,6 @@ class DebugInfoImpl {
// {mutex_} protects all fields below.
mutable base::Mutex mutex_;
// Cache a fixed number of WasmCode objects that were generated for debugging.
// This is useful especially in stepping, because stepping code is cleared on
// every pause and re-installed on the next step.
// This is a LRU cache (most recently used entries first).
static constexpr size_t kMaxCachedDebuggingCode = 3;
struct CachedDebuggingCode {
int func_index;
OwnedVector<const int> breakpoint_offsets;
int dead_breakpoint;
WasmCode* code;
};
std::vector<CachedDebuggingCode> cached_debugging_code_;
// Names of exports, lazily derived from the exports table.
std::unique_ptr<std::map<ImportExportKey, wasm::WireBytesRef>> export_names_;