DDC does not build a working SDK with CFE constants flag enabled

[jmesserly]

Use the instructions and patches here to enable the constants flag: #36479

DDC's Kernel-backend compiled SDK will not load. I've found a few issues so far:

• the SDK's internal annotations are not found. For example @nullCheck, @notNull, @JSExportName, @NoReifyGenerics, and probably other critical ones such as @JsPeerIterface.
• static calls seem to be tagging the target with RTTI, as if it were a tearoff. As a result, we attempt to create a dart.FunctionType before it has been defined. This might partly be an issue with @ReifyFunctionTypes, but even so, we should not be reifying in these cases as it is unnecessary. We'll need to double check that this works properly for user code.

Also a few minor/trivial issues (not P1) such as:

• integer constants are generated as if they were doubles: 1.0 instead of 1. This is valid, but has a very slight code size/readability cost.

[jmesserly]

I found a serious perf issue: #36535. My hope is that it isn't bad enough to require a fix in 2.3

[jmesserly]

I'm testing https://dart-review.googlesource.com/c/sdk/+/98875.
Update: there's a new testing CL, see my comment below

Once it passes, we can pull out the "pkg/dev_compiler" fixes into a CL and submit that separately. But for now I've merged it with the patches in #36479 so I can test how DDC is doing.

[sigmundch]

@jmesserly - I just added the 2.3 milestone, I assume this is necessary before we ship, correct?

[jmesserly]

ah, thank you. I meant to put it in 2.3, yup.

[jmesserly]

I'm now testing a fix here: https://dart-review.googlesource.com/c/sdk/+/98927

Once DDC is green, I can pull out the DDC changes. It also includes a 1-liner CFE fix for #36545

[jmesserly]

I uploaded a few more workarounds:

• there's some unusual CFE behavior where annotations end up as ConstantExpressions wrapping an UnevaluatedConstant. (this broke DDC's ability to pattern match certain annotations, such as @JS())
• external factories appear to be eliminated currently, but are preserved with the constants flag. The compiler did not expect this and tried to emit a Procedure with a null function body.

I'm dry-running now. I think those will fix most/all of the remaining test failures.

[jmesserly]

Last night's test run found a few more issues. Based on local testing, I believe those are now fixed, so I made a CL that is DDC-only. https://dart-review.googlesource.com/c/sdk/+/99240. I'm also doing another test run on the above CL that contains the code to flip the flag.

[jmesserly]

The CL passed on both with and without the constants flag globally enabled (other than 2 co19 tests that are failing on other platforms too w/ constants flag, so not a DDC issue). I've sent it out for review.

[sigmundch]

@jmesserly - just saw that your CL landed, woohoo!

Is it safe to close this issue at this time?