diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/tools/wasm2js.cpp | 33 | ||||
| -rw-r--r-- | src/wasm2js.h | 2 |
2 files changed, 31 insertions, 4 deletions
diff --git a/src/tools/wasm2js.cpp b/src/tools/wasm2js.cpp index e7b62c16a..7f3433bb7 100644 --- a/src/tools/wasm2js.cpp +++ b/src/tools/wasm2js.cpp @@ -141,7 +141,7 @@ static void replaceInPlaceIfPossible(Ref target, Ref value) { } } -static void optimizeJS(Ref ast) { +static void optimizeJS(Ref ast, Wasm2JSBuilder::Flags flags) { // Helpers auto isBinary = [](Ref node, IString op) { @@ -262,8 +262,21 @@ static void optimizeJS(Ref ast) { node[1]->setString(L_NOT); node[3]->setNull(); } else if (isOrZero(node) || isTrshiftZero(node)) { - // Just being different from 0 is enough, casts don't matter. - return node[2]; + // Just being different from 0 is enough, casts don't matter. However, + // in deterministic mode we care about corner cases that would trap in + // wasm, like an integer divide by zero: + // + // if ((1 / 0) | 0) => condition is Infinity | 0 = 0 which is falsey + // + // while + // + // if (1 / 0) => condition is Infinity which is truthy + // + // Thankfully this is not common, and does not occur on % (1 % 0 is a NaN + // which has the right truthiness). + if (!(flags.deterministic && isBinary(node[2], DIV))) { + return node[2]; + } } return node; }; @@ -511,7 +524,7 @@ static void emitWasm(Module& wasm, Wasm2JSBuilder wasm2js(flags, options); auto js = wasm2js.processWasm(&wasm, name); if (options.optimizeLevel >= 2) { - optimizeJS(js); + optimizeJS(js, flags); } Wasm2JSGlue glue(wasm, output, flags, name); glue.emitPre(); @@ -849,6 +862,18 @@ int main(int argc, const char* argv[]) { Options::Arguments::Zero, [&](Options* o, const std::string& argument) { flags.emscripten = true; }) .add( + "--deterministic", + "", + "Replace WebAssembly trapping behavior deterministically " + "(the default is to not care about what would trap in wasm, like a load " + "out of bounds or integer divide by zero; with this flag, we try to be " + "deterministic at least in what happens, which might or might not be " + "to trap like wasm, but at least should not vary)", + Options::Arguments::Zero, + [&](Options* o, const std::string& argument) { + flags.deterministic = true; + }) + .add( "--symbols-file", "", "Emit a symbols file that maps function indexes to their original names", diff --git a/src/wasm2js.h b/src/wasm2js.h index 4db734203..1d8003323 100644 --- a/src/wasm2js.h +++ b/src/wasm2js.h @@ -120,10 +120,12 @@ class Wasm2JSBuilder { public: struct Flags { + // see wasm2js.cpp for details bool debug = false; bool pedantic = false; bool allowAsserts = false; bool emscripten = false; + bool deterministic = false; std::string symbolsFile; }; |