bad values for sin and cos methods for optimized code

[devoncarew]

This can be seen in the solar example, and in the following test case:

import 'dart:math' as math;

void main() {
  doMath(true);

  for (int i = 0; i < 1000000; i++) {
    if (!doMath()) {
      print("bad trig results at iteration $i");

      doMath(true);

      return;
    }
  }

  doMath(true);
}

bool doMath([bool doPrint = false]) {
  double angle = math.PI / 2;

  double sVal = math.sin(angle);
  double cVal = math.cos(angle);

  if (doPrint) {
    print("sin($angle) = $sVal, cos($angle) = $cVal");
  }

  return sVal != cVal;
}

I get the following results:

sin(1.5707963267948966) = 1.0, cos(1.5707963267948966) = 6.123031769111886e-17
bad trig results at iteration 2999
sin(1.5707963267948966) = 1.0, cos(1.5707963267948966) = 1.0

I.e. the results go bad after the 3000th iteration of calling the method.

[devoncarew]

Possibly related to this CL: https://codereview.chromium.org//22266005 ?

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cc @sgmitrovic.
cc @iposva-google.

[mraleph]

UnaryMathInstr::AttributesEqual should compare kind_

right now all UnaryMathInstr instances are considered equal as long as they have the same arguments independently of what they actually compute (so here math.cos(angle) will be replaced with the result of math.sin(angle)).

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Set owner to @sgmitrovic.

Thanks for reporting this bug!

Fixed in r26014. Fix is has been identified by vegorov.

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Added Fixed label.