dart2js: improve ssa utilization of bool value types

pkg/compiler/lib/src/ssa/optimize.dart

Index: pkg/compiler/lib/src/ssa/optimize.dart
diff --git a/pkg/compiler/lib/src/ssa/optimize.dart b/pkg/compiler/lib/src/ssa/optimize.dart
index 07611f654a3292066d02ec241076f47e28dc7c3b..b904d3252455afe66cf0cf05745216383a180c97 100644
--- a/pkg/compiler/lib/src/ssa/optimize.dart
+++ b/pkg/compiler/lib/src/ssa/optimize.dart
@@ -200,6 +200,45 @@ class SsaInstructionSimplifier extends HBaseVisitor
     return node;
   }
 
+  ConstantValue getConstantFromType(HInstruction node) {
+    if (node.isValue() && !node.canBeNull()) {
+      ValueTypeMask valueMask = node.instructionType;
+      if (valueMask.value.isBool) {
+        return valueMask.value;
+      }
+      // TODO(het): consider supporting other values (short strings?)
+    }
+    return null;
+  }
+
+  void propagateConstantValueToUses(HInstruction known) {

[sra1, 2015/10/01 01:48:00]

Maybe call it 'node'.
It is not known until we test 'value'.

[Harry Terkelsen, 2015/10/01 21:06:36]

Done.

+    if (known.usedBy.isEmpty) return;
+    ConstantValue value = getConstantFromType(known);
+    if (value != null) {
+      // If this instruction is ever assigned to, then do not propagate the
+      // value since it may

[sra1, 2015/10/01 01:48:00]

Not needed.
Only parameters (and Locals) can be assigned, which is taken care of under
visitParameterValue.
The other cases are invocations which return a value and that is never 'punned'
as a location like a parameter.

[Harry Terkelsen, 2015/10/01 21:06:36]

Done.

+      if (known.usedBy.any(
+          (user) => user is HLocalSet && identical(user.local, known))) {
+        return;
+      }
+      for (HInstruction user in known.usedBy.toList()) {
+        user.changeUse(known, graph.addConstant(value, compiler));

[sra1, 2015/10/01 01:48:00]

You can lift this out of the loop:

HInstruction constant = graph.addConstant(value, compiler);

[Harry Terkelsen, 2015/10/01 21:06:36]

Done.

+      }
+    }
+  }
+
+  HInstruction visitParameterValue(HParameterValue node) {
+    // It is possible for the parameter value to be assigned to in the function
+    // body. If that happens then we should not forward the constant value to
+    // its uses since they are shadowed by the assignment.

[sra1, 2015/10/01 01:48:00]

"since the uses reachable from the assignment may have values in addition to the
constant passed to the function."
(there is not really any shadowing)

The question I have is this: is the HLocalSet pattern match good enough?

foo(p) {
  for(int i = 0; i < 10; i++) {
    if (p is bool) p = 123;
  }
  return p;
}

Is the p under the 'if' guarded by a HTypeKnown?

I think we are safe since we do ssa convert many uses, just not before the first
merge or in code containing try-catch-finally.

[Harry Terkelsen, 2015/10/01 21:06:36]

I just tried out this program. The p is not recognized as being the lhs of an
HLocalSet, but it seems like p is ssa converted inside the loop body:

    foo: function(p) {
      var i;
      for (p = true, i = 0; i < 10; ++i)
        if (typeof p === "boolean")
          p = 123;
      return p;
    },

+    if (node.usedBy.any((user) =>
+            user is HLocalSet && identical(user.local, node))) {
+      return node;
+    }
+    propagateConstantValueToUses(node);
+    return node;
+  }
+
   HInstruction visitBoolify(HBoolify node) {
     List<HInstruction> inputs = node.inputs;
     assert(inputs.length == 1);
@@ -372,6 +411,7 @@ class SsaInstructionSimplifier extends HBaseVisitor
   }
 
   HInstruction visitInvokeDynamicMethod(HInvokeDynamicMethod node) {
+    propagateConstantValueToUses(node);
     if (node.isInterceptedCall) {
       HInstruction folded = handleInterceptedCall(node);
       if (folded != node) return folded;
@@ -806,6 +846,7 @@ class SsaInstructionSimplifier extends HBaseVisitor
   }
 
   HInstruction visitInvokeDynamicGetter(HInvokeDynamicGetter node) {
+    propagateConstantValueToUses(node);
     if (node.isInterceptedCall) {
       HInstruction folded = handleInterceptedCall(node);
       if (folded != node) return folded;
@@ -867,6 +908,7 @@ class SsaInstructionSimplifier extends HBaseVisitor
   }
 
   HInstruction visitInvokeStatic(HInvokeStatic node) {
+    propagateConstantValueToUses(node);
     if (node.element == backend.getCheckConcurrentModificationError()) {
       if (node.inputs.length == 2) {
         HInstruction firstArgument = node.inputs[0];
@@ -1306,13 +1348,6 @@ class SsaLiveBlockAnalyzer extends HBaseVisitor {
       } else {
         markBlockLive(instruction.elseBlock);
       }
-    } else if (condition.isValue()) {
-      ValueTypeMask valueType = condition.instructionType;
-      if (valueType.value == true) {
-        markBlockLive(instruction.thenBlock);
-      } else {
-        markBlockLive(instruction.elseBlock);
-      }
     } else {
       visitControlFlow(instruction);
     }