Merge libv1.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart b/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
index 0f887b1a416f76e381a8dbb6a5bf45165e10b750..b416c3fecbb98e23be5d2912a7a242f4bf5e2ac1 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
@@ -287,7 +287,9 @@ class SsaLiveIntervalBuilder extends HBaseVisitor {
 
     // If the block is a loop header, we can remove the loop marker,
     // because it will just recompute the loop phis.
-    if (block.isLoopHeader()) {
+    // We also check if this loop header has any back edges. If not,
+    // we know there is no loop marker for it.
+    if (block.isLoopHeader() && block.predecessors.length > 1) {
       updateLoopMarker(block);
     }
   }
@@ -507,16 +509,15 @@ class VariableNamer {
         name = names.ownName[temp];
       } while (name == null && temp is HCheck);
       if (name != null) return addAllocatedName(instruction, name);
-    } else if (instruction is HParameterValue) {
-      HParameterValue parameter = instruction;
-      name = parameterNames[parameter.sourceElement];
-      if (name == null) {
-        name = allocateWithHint(parameter.sourceElement.name.slowToString());
-      }
-      return addAllocatedName(instruction, name);
     }
 
-    if (instruction.sourceElement != null) {
+    // The dom/html libraries have inline JS code that reference	
+    // parameter names directly. Long-term such code will be rejected.
+    // Now, just don't mangle the parameter name.
+    if (instruction is HParameterValue
+        && instruction.sourceElement.enclosingElement.isNative()) {
+      name = instruction.sourceElement.name.slowToString();
+    } else if (instruction.sourceElement != null) {
       name = allocateWithHint(instruction.sourceElement.name.slowToString());
     } else {
       // We could not find an element for the instruction. If the
@@ -534,6 +535,9 @@ class VariableNamer {
   }
 
   String addAllocatedName(HInstruction instruction, String name) {
+    if (instruction is HParameterValue) {
+      parameterNames[instruction.sourceElement] = name;
+    }
     usedNames.add(name);
     names.addNameUsed(name);
     names.ownName[instruction] = name;
@@ -611,11 +615,11 @@ class SsaVariableAllocator extends HBaseVisitor {
    * have no users or that are generated at use site does not need a name.
    */
   bool needsName(HInstruction instruction) {
-    if (instruction.usedBy.isEmpty) return false;
     // TODO(ngeoffray): locals/parameters are being generated at use site,
     // but we need a name for them. We should probably not make
     // them generate at use site to make things simpler.
     if (instruction is HLocalValue && instruction is !HThis) return true;
+    if (instruction.usedBy.isEmpty) return false;
     if (generateAtUseSite.contains(instruction)) return false;
     // A [HCheck] instruction that has control flow needs a name only if its
     // checked input needs a name (e.g. a check [HConstant] does not