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Incorrectly eliminated cast on numeric type in generic method #35618

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munificent opened this Issue Jan 9, 2019 · 2 comments

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munificent commented Jan 9, 2019

If I run this program:

T sum<T extends num>(T value) {
  return 0 as T;
}

void main() {
  double d;
  print(sum(d));
  print(sum(d).isNaN);
}

On the bleeding edge VM:

Dart VM version: 2.2.0-edge.13a689f0fdb8de75f64db488d361edadae578d12 (Tue Jan 8 23:56:23 2019 +0000) on "macos_x64"

I get:

0
Unhandled exception:
type 'int' is not a subtype of type 'double' in type cast
#0      sum (file:///Users/rnystrom/temp/temp.dart:2:12)
#1      main (file:///Users/rnystrom/temp/temp.dart:8:9)
#2      _startIsolate.<anonymous closure> (dart:isolate/runtime/libisolate_patch.dart:289:19)
#3      _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)

Note the first zero. The first call to sum() succeeds even though that cast should certainly fail. Interestingly, the call to isNaN apparently causes the cast inside the body of the function to be performed. I'm assuming some optimization pass is incorrectly eliminating the cast in the first call.

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mraleph commented Jan 10, 2019

This is a CFE bug:

 library from "file:///tmp/x.dart" as x {
   static method sum<T extends core::num = core::num>(x::sum::T value) → x::sum::T {
     return 0 as x::sum::T;
   }
   static method main() → void {
     core::double d;
     core::print(x::sum<core::num>(d));
     core::print(x::sum<core::double>(d).{core::num::isNaN});
   }
 }

@mraleph mraleph added area-front-end and removed area-vm labels Jan 10, 2019

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munificent commented Jan 10, 2019

Thanks, I wasn't sure where the in pipeline the bug happened, so I randomly picked "area-vm". :)

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