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Merged
tlively merged 1 commit into from
Apr 20, 2026
+60 −20
Merged

Look at fallthrough when deleting branch hints #8630

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41 changes: 21 additions & 20 deletions src/passes/InstrumentBranchHints.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -98,6 +98,7 @@

#include "ir/effects.h"
#include "ir/names.h"
#include "ir/properties.h"
#include "ir/utils.h"
#include "pass.h"
#include "support/string.h"
Expand Down Expand Up @@ -231,18 +232,6 @@ struct InstrumentationProcessor : public WalkerPass<PostWalker<Sub>> {

Super::doWalkModule(module);
}

// Helpers

// Check if an expression's condition is instrumented, and return the
// instrumentation call if so. Otherwise return null.
Call* getInstrumentation(Expression* condition) {
auto* call = condition->dynCast<Call>();
if (!call || call->target != logBranch) {
return nullptr;
}
return call;
}
};

struct DeleteBranchHints : public InstrumentationProcessor<DeleteBranchHints> {
Expand All @@ -251,15 +240,27 @@ struct DeleteBranchHints : public InstrumentationProcessor<DeleteBranchHints> {
// The set of IDs to delete.
std::unordered_set<Index> idsToDelete;

std::optional<uint32_t> getBranchID(Expression* condition,
const PassOptions& passOptions,
Module& wasm) {
auto* call =
Properties::getFallthrough(condition, getPassOptions(), *getModule())
->dynCast<Call>();
if (!call || call->target != logBranch || call->operands.size() != 3) {
return std::nullopt;
}
auto* c = call->operands[2]->dynCast<Const>();
if (!c || c->type != Type::i32) {
return std::nullopt;
}
return c->value.geti32();
}

template<typename T> void processCondition(T* curr) {
if (auto* call = getInstrumentation(curr->condition)) {
if (auto* c = call->operands[2]->template dynCast<Const>()) {
auto id = c->value.geti32();
if (idsToDelete.contains(id)) {
// Remove the branch hint.
getFunction()->codeAnnotations[curr].branchLikely = {};
}
}
if (auto id = getBranchID(curr->condition, getPassOptions(), *getModule());
id && idsToDelete.contains(*id)) {
// Remove the branch hint.
getFunction()->codeAnnotations[curr].branchLikely = std::nullopt;
}
}

Expand Down
39 changes: 39 additions & 0 deletions test/lit/passes/delete-branch-hints.wast
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,8 @@

;; CHECK: (type $1 (func (param i32 i32 i32) (result i32)))

;; CHECK: (type $2 (func (param i32) (result i32)))

;; CHECK: (import "fuzzing-support" "log-branch" (func $log (type $1) (param i32 i32 i32) (result i32)))
(import "fuzzing-support" "log-branch" (func $log (param i32 i32 i32) (result i32)))

Expand Down Expand Up @@ -118,4 +120,41 @@
)
)
)

;; CHECK: (func $stacky (type $2) (param $c i32) (result i32)
;; CHECK-NEXT: (block $l (result i32)
;; CHECK-NEXT: (br_if $l
;; CHECK-NEXT: (i32.const 42)
;; CHECK-NEXT: (block (result i32)
;; CHECK-NEXT: (nop)
;; CHECK-NEXT: (call $log
;; CHECK-NEXT: (local.get $c)
;; CHECK-NEXT: (i32.const 1)
;; CHECK-NEXT: (i32.const 10)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $stacky (param $c i32) (result i32)
block $l (result i32)
i32.const 42
;; Because the parser greedily pulls previous none-typed expressions into
;; block, this condition will be parsed as this:
;;
;; (block
;; (nop)
;; (call $log-branch ...))
;; )
;;
;; We must be able to find and handle this pattern to remove the hint.
nop
local.get $c
i32.const 1
i32.const 10
call $log
(@metadata.code.branch_hint "\01")
br_if $l
end
)
)
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