Redo "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 e3a107b5abc90afdae0ffa1329418bcfa668b437..4122364bcf5d8679114d48b0f188adeddc22c423 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/types_propagation.dart
@@ -140,21 +140,37 @@ class SsaTypePropagator extends HBaseVisitor implements OptimizationPhase {
   }
 
   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.
+      if (checkedType.isNumber()
+          && !checkedType.isDouble()
+          && inputType.isIntegerOrNull()) {
+        instruction.checkedType = HType.INTEGER;
+      } else if (checkedType.isInteger() && !inputType.isIntegerOrNull()) {
+        instruction.checkedType = HType.NUMBER;
+      }
+    }
+
+    HType outputType = checkedType.intersection(inputType, compiler);
+    if (outputType.isConflicting()) {
+      // Intersection of double and integer conflicts (is empty), but JS numbers
+      // can be both int and double at the same time.  For example, the input
+      // can be a literal double '8.0' that is marked as an integer (because 'is
+      // int' will return 'true').  What we really need to do is make the
+      // overlap between int and double values explicit in the HType system.
+      if (inputType.isIntegerOrNull() && checkedType.isDoubleOrNull()) {
+        if (inputType.canBeNull() && checkedType.canBeNull()) {
+          outputType = HType.DOUBLE_OR_NULL;
+        } else {
+          outputType = HType.DOUBLE;
+        }
+      }
     }
-    return oldType;
+    return outputType;
   }
 
   HType visitTypeKnown(HTypeKnown instruction) {