Branch hint fuzz bug with --code-pushing

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Quiet
Tech stack
wasm
Domain
compilers, tooling

Research direction

Start with repro.sh and the attached repro.zip, then run the shown bin/wasm-opt sequence to confirm the branch-hint change. Compare the original and final instrumentation around --code-pushing and inspect the relevant wasm-opt pass entry points. Done means the branch identity or expected behavior is explained and covered by a regression test.

Written by the indexing model from the issue text.

Description

repro.zip

$ ./repro.sh
+ bin/wasm-opt -all b.wast -S -o b.inst.wast --randomize-branch-hints --instrument-branch-hints -g
+ bin/wasm-opt -all b.inst.wast --fuzz-exec-before
[fuzz-exec] export test
[LoggingExternalInterface log-branch 1 1 0]
[LoggingExternalInterface logging 0]
[LoggingExternalInterface log-branch 2 1 1]
warning: no passes specified, not doing any work
warning: no output file specified, not emitting output
+ bin/wasm-opt -all b.inst.wast -S -o b.de_inst.wast --delete-branch-hints=1 --deinstrument-branch-hints -g
+ bin/wasm-opt -all b.de_inst.wast -S -o b.opted.wast -g --code-pushing
+ bin/wasm-opt -all b.opted.wast -S -o b.final.wast --instrument-branch-hints -g
+ bin/wasm-opt -all b.final.wast --fuzz-exec-before
[fuzz-exec] export test
[LoggingExternalInterface logging 0]
[LoggingExternalInterface log-branch 1 1 1]
warning: no passes specified, not doing any work
warning: no output file specified, not emitting output

So it looks like branch hint number 1 changed results, but looking at the original instrumentation and the final instrumentation, it's maybe a completely different branch??? Not really sure what the correct next step is.

Dominant language
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