dart2js: Insert HTypeKnown refinement nodes on dominated edges of HPhi nodes.

dart2js: Insert HTypeKnown refinement nodes on dominated edges of HPhi nodes.

Consider:

    value ??= "";

We fail to infer in SSA type progagation that value is non-null.

At CFG level this looks like

    if (value == null) {
      value = "";
    } else {
      // There is always an empty else-block.
    }
   value1 = phi("", value);

Previously we considered the phi use of 'value' to be outside the
region dominated by the condition 'value != null', leaving nowhere to
attach the type refinement. Now we consider it inside the region,
allowing:

    if (value == null) {
      value = "";
    } else {
      value1 = HTypeKnown(not-null, value);
    }
    value2 = phi("", value1);

Type propagation now determines value2 is non-null.

R=efortuna@google.com

Committed: https://github.com/dart-lang/sdk/commit/49e78d7e32dd26b25fb7def5b62f26fde1870675

[sra1, 2017-03-20 20:32:32]

Patchset #2 (id:20001) has been deleted

[sra1, 2017-03-20 20:34:08]

Patchset #1 (id:1) has been deleted

[sra1, 2017-03-20 20:34:15]

Patchset #1 (id:40001) has been deleted

[sra1, 2017-03-21 00:26:19]

Patchset #1 (id:60001) has been deleted

[sra1, 2017-03-21 00:56:29]

Patchset #1 (id:80001) has been deleted

[sra1, 2017-03-21 01:48:02]

Patchset #1 (id:100001) has been deleted

[sra1, 2017-03-21 07:04:49]

sra@google.com changed reviewers:
+ sigmund@google.com

[sra1, 2017-03-22 23:01:22]

https://codereview.chromium.org/2755353003/diff/120001/pkg/compiler/lib/src/s...
File pkg/compiler/lib/src/ssa/types_propagation.dart (right):

https://codereview.chromium.org/2755353003/diff/120001/pkg/compiler/lib/src/s...
pkg/compiler/lib/src/ssa/types_propagation.dart:411:
receiver.replaceAllUsersDominatedBy(converted.next, converted);
We should try to reuse the computed dominated uses here rather than recomputing
them.

[sra1, 2017-04-03 18:26:52]

sra@google.com changed reviewers:
+ efortuna@google.com

[Emily Fortuna, 2017-04-03 20:48:46]

lgtm

https://codereview.chromium.org/2755353003/diff/120001/pkg/compiler/lib/src/s...
File pkg/compiler/lib/src/ssa/nodes.dart (right):

https://codereview.chromium.org/2755353003/diff/120001/pkg/compiler/lib/src/s...
pkg/compiler/lib/src/ssa/nodes.dart:1418: if (--usersInCurrentBlock == 0) break;
small preference for doing the decrement in a separate statement because I
always have to remind myself which value is being returned when it's
before/after the variable, but not a strong requirement. It's reasonably simple
code.

https://codereview.chromium.org/2755353003/diff/120001/pkg/compiler/lib/src/s...
File pkg/compiler/lib/src/ssa/optimize.dart (right):

https://codereview.chromium.org/2755353003/diff/120001/pkg/compiler/lib/src/s...
pkg/compiler/lib/src/ssa/optimize.dart:732: // statements or ends with a switch.
👏👏👏 (that's a hand clapping emoji in case it's not clear)

[sra1, 2017-04-06 17:44:15]

Description was changed from

==========
dart2js: Insert HTypeKnown refinement nodes on dominated edges of HPhi nodes.

Consider:

    value ??= "";

We fail to infer in SSA type progagation that value is non-null.

At CFG level this looks like

    if (value == null) {
      value = "";
    } else {
      // There is always an empty else-block.
    }
   value1 = phi("", value);

Previously we considered the phi use of 'value' to be outside the
region dominated by the condition 'value != null', leaving nowhere to
attach the type refinement. Now we consider it inside the region,
allowing:

    if (value == null) {
      value = "";
    } else {
      value1 = HTypeKnown(not-null, value);
    }
    value2 = phi("", value1);

Type propagation now determines value2 is non-null.
==========

to

==========
dart2js: Insert HTypeKnown refinement nodes on dominated edges of HPhi nodes.

Consider:

    value ??= "";

We fail to infer in SSA type progagation that value is non-null.

At CFG level this looks like

    if (value == null) {
      value = "";
    } else {
      // There is always an empty else-block.
    }
   value1 = phi("", value);

Previously we considered the phi use of 'value' to be outside the
region dominated by the condition 'value != null', leaving nowhere to
attach the type refinement. Now we consider it inside the region,
allowing:

    if (value == null) {
      value = "";
    } else {
      value1 = HTypeKnown(not-null, value);
    }
    value2 = phi("", value1);

Type propagation now determines value2 is non-null.

R=efortuna@google.com

Committed:
https://github.com/dart-lang/sdk/commit/49e78d7e32dd26b25fb7def5b62f26fde1870675
==========

[sra1, 2017-04-06 17:44:16]

Committed patchset #2 (id:140001) manually as
49e78d7e32dd26b25fb7def5b62f26fde1870675 (presubmit successful).