Bug 232754 – When inlining NewSymbol in the DFG don't universally call ToString on the input

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Lukas Bernhard]

During differential testing of webkit I found a sample triggering a miscomputation in the baseline execution. The sample is larger than I'd like it to be, unfortunately all further minimizations I attempted did break the differential behavior.

The sample is invoked as:
WebKitBuild/Release/bin/jsc --validateOptions=true --useConcurrentJIT=false --useConcurrentGC=false --thresholdForJITSoon=10 --thresholdForJITAfterWarmUp=10 --thresholdForOptimizeAfterWarmUp=100 --thresholdForOptimizeAfterLongWarmUp=100 --thresholdForOptimizeSoon=100 --thresholdForFTLOptimizeAfterWarmUp=1000 --thresholdForFTLOptimizeSoon=1000 --validateBCE=true --useFTLJIT=true sample.js


function main() {
    let v83;
    let v102;
    const v30 = []; 
    
    for (let v56 = 0; v56 < 80; v56++) {
        let v57 = 0;
        const v59 = []; 
        const v61 = []; 
            
        v63 = [0.0];
        function v65(v66,v67,v68) {
            const v69 = v63 * v30;
            const v70 = Uint16Array;
            let v72 = 0;
            const v76 = [0,0,v61,0];
            const v78 = []; 
                
            v79 = {__proto__:[], length:"a"};
            const v81 = [0,0,v79,v76];
            v83 = [v65];
            Reflect.apply(v81.map,v67,[v65]);
                
            for (const v86 of v68) {
                v87 = v59 << v86;
                const v91 = new Int32Array(0);
                const v92 = undefined;
                const v94 = Symbol(undefined);
                v102 = v94.description;
                v57++;
            }   
        }   
        const v105 = v65(0.0,"aaaa",v63);
    }
        
    print(v102); // undefined with and without FTL
    print(typeof v102); // string without FTL, undefined with FTL (also undefined in spidermonkey)
}
main();

[Saam Barati]

I can't reproduce this on r285408. Can you still reproduce it?

[Lukas Bernhard]

The issue still reproduces for me on git 016f88c15b9bf0ebae0090babdad6a34e783d1b5
Just in case it somehow depends on build options, here are the ones I used:
./Tools/Scripts/build-jsc --jsc-only --release --cmakeargs="-ENABLE_STATIC_JSC=ON -DCMAKE_C_COMPILER='/usr/bin/clang-12' -DCMAKE_CXX_COMPILER='/usr/bin/clang++-12' -DCMAKE_CXX_FLAGS='-fsanitize-coverage=trace-pc-guard -O3 -lrt -fuse-ld=lld'"

[Saam Barati]

Thanks, I can reproduce it. I must've been running it with the wrong option earlier.

[Saam Barati]

Created attachment 443634 [details]
Patch

[Robin Morisset]

Comment on attachment 443634 [details]
Patch

r=me

[EWS]

Committed r285525 (244042@main): <https://commits.webkit.org/244042@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 443634 [details].

[Radar WebKit Bug Importer]

<rdar://problem/85215832>