Bug 165946 – B3::DoubleToFloatReduction will accidentally convince itself it converted a Phi from Double to Float and then convert uses of that Phi into a use of FloatToDouble(@Phi)

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Saam Barati]

It's causing a bug somewhere in a Wasm program by making causing something like transformation to happen:

(Note this is IR just after generating)
```
    Float @2342 = Phi(ReadsLocalState)
    ...
    Float @1772 = BitwiseCast(@2228)
    Float @1773 = Identity(@2342)
    Float @1774 = Mul(@1772, @2342)

```

=>

```
    Float @2342 = Phi(ReadsLocalState)
    Float @1772 = BitwiseCast(@2228)
    Double @3202 = FloatToDouble(@2342)
    Float @1774 = Mul(@1772, @3202)
```

[Saam Barati]

My hypothesis is that this:

```
    void convertPhi(Value* phi)
    {
        ASSERT(phi->opcode() == Phi);
        phi->setType(Float);
        m_convertedPhis.add(phi);
    }
```

should become:

```
    void convertPhi(Value* phi)
    {
        ASSERT(phi->opcode() == Phi);
        if (phi->type() == Double) {
            phi->setType(Float);
            m_convertedPhis.add(phi);
        }
    }
```

Otherwise we'll cast all users of a Phi to use FloatToDouble, even though they want float!

[Saam Barati]

Created attachment 297359 [details]
patch

[WebKit Commit Bot]

Attachment 297359 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/b3/testb3.cpp:4579:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:4581:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:4584:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
Total errors found: 3 in 3 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Keith Miller]

Comment on attachment 297359 [details]
patch

View in context: https://bugs.webkit.org/attachment.cgi?id=297359&action=review

r=me.

> Source/JavaScriptCore/ChangeLog:14
> +        Double uses by changing them to be uses of ConvertFloatToDouble on the Phi

I would say ConvertFloatToDouble on the Phi, instead of the Phi itself. I had to reread that a couple of times.

[Saam Barati]

Created attachment 297361 [details]
patch for landing

[WebKit Commit Bot]

Attachment 297361 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/b3/testb3.cpp:4579:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:4581:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
ERROR: Source/JavaScriptCore/b3/testb3.cpp:4584:  When wrapping a line, only indent 4 spaces.  [whitespace/indent] [3]
Total errors found: 3 in 3 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Build Bot]

Comment on attachment 297361 [details]
patch for landing

Attachment 297361 [details] did not pass mac-debug-ews (mac):
Output: http://webkit-queues.webkit.org/results/2739762

New failing tests:
http/tests/navigation/keyboard-events-during-provisional-navigation.html

[Build Bot]

Created attachment 297368 [details]
Archive of layout-test-results from ews112 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews112  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Saam Barati]

This crash looks unrelated to my change. It looks like a GC crash.

[WebKit Commit Bot]

Comment on attachment 297361 [details]
patch for landing

Clearing flags on attachment: 297361

Committed r209953: <http://trac.webkit.org/changeset/209953>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.