Separate HTypeConversion checked type from output type.

sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart b/sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart
index d861e344333bedf062fe52e82a3779b44327d777..2bc6ed0182a0da7db7c6b638b98cbba8df5233e9 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart
@@ -149,21 +149,21 @@ abstract class SsaTypePropagator extends HBaseVisitor
   }
 
   HType visitTypeConversion(HTypeConversion instruction) {
-    HType oldType = instruction.instructionType;
-    // Do not change a checked mode check.
-    if (instruction.isCheckedModeCheck) return oldType;
-    // We must make sure a type conversion for receiver or argument check
-    // does not try to do an int check, because an int check is not enough.
-    // We only do an int check if the input is integer or null.
-    HInstruction checked = instruction.checkedInput;
-    if (oldType.isNumber()
-        && !oldType.isDouble()
-        && checked.isIntegerOrNull()) {
-      return HType.INTEGER;
-    } else if (oldType.isInteger() && !checked.isIntegerOrNull()) {
-      return HType.NUMBER;
+    HType inputType = instruction.checkedInput.instructionType;
+    HType checkedType = instruction.checkedType;
+    if (instruction.isArgumentTypeCheck || instruction.isReceiverTypeCheck) {
+      // We must make sure a type conversion for receiver or argument check
+      // does not try to do an int check, because an int check is not enough.
+      // We only do an int check if the input is integer or null.

[sra1, 2013/10/22 22:56:16]

It would be nice to make checkedType final.

What I don't understand here is what does 'not enough' mean.
Why is the HTypeConversion originally created with the 'wrong' type?

[ngeoffray, 2013/10/24 06:50:55]

Not enough because the check we emit is (a | 0) === a, which does not cover all
our ints. Note that a checked mode HTypeConversion uses a helper that does the
right int check.

It is created with the 'wrong' type because at the creation point, we
unconditionally do it. This code here makes the conversion correct in case the
input is not int or null.

+      if (checkedType.isNumber()
+          && !checkedType.isDouble()
+          && inputType.isIntegerOrNull()) {
+        instruction.checkedType = HType.INTEGER;
+      } else if (checkedType.isInteger() && !inputType.isIntegerOrNull()) {
+        instruction.checkedType = HType.NUMBER;
+      }
     }
-    return oldType;
+    return checkedType.intersection(inputType, compiler);
   }
 
   HType visitTypeKnown(HTypeKnown instruction) {