Return to more structured type rules for block and if (#1148)

* if a block has a concrete final element (or a break with a value), then even if it has an unreachable child, keep it with that concrete type. this means we no longe allow the silly case of a block with an unreachable in the middle and a concrete as the final element while the block is unreachable - after this change, the block would have the type of the final element

* if an if has a concrete element in one arm, make it have that type as a result, even if the if condition is unreachable, to parallel block

* make type rules for brs and switches simpler, ignore whether they are reachable or not. whether they are dead code should not affect how they influence other types in our IR.

1 files changed, 7 insertions, 7 deletions

diff --git a/src/ast/branch-utils.h b/src/ast/branch-utils.h
index 77ec70753..05ead8571 100644
--- a/src/ast/branch-utils.h
+++ b/src/ast/branch-utils.h
@@ -103,11 +103,11 @@ inline std::set<Name> getBranchTargets(Expression* ast) {
 // Finds if there are branches targeting a name. Note that since names are
 // unique in our IR, we just need to look for the name, and do not need
 // to analyze scoping.
-// By default we ignore untaken branches. You can set named to
-// note those as well, then any named branch is noted, even if untaken
+// By default we consider untaken branches (so any named use). You can unset named to
+// avoid that (and only note branches that are not obviously unreachable)
 struct BranchSeeker : public PostWalker<BranchSeeker> {
   Name target;
-  bool named = false;
+  bool named = true;
 
   Index found;
   WasmType valueType;
@@ -144,16 +144,18 @@ struct BranchSeeker : public PostWalker<BranchSeeker> {
     if (curr->default_ == target) noteFound(curr->value);
   }
 
-  static bool has(Expression* tree, Name target) {
+  static bool hasTaken(Expression* tree, Name target) {
     if (!target.is()) return false;
     BranchSeeker seeker(target);
+    seeker.named = false;
     seeker.walk(tree);
     return seeker.found > 0;
   }
 
-  static Index count(Expression* tree, Name target) {
+  static Index countTaken(Expression* tree, Name target) {
     if (!target.is()) return 0;
     BranchSeeker seeker(target);
+    seeker.named = false;
     seeker.walk(tree);
     return seeker.found;
   }
@@ -161,7 +163,6 @@ struct BranchSeeker : public PostWalker<BranchSeeker> {
   static bool hasNamed(Expression* tree, Name target) {
     if (!target.is()) return false;
     BranchSeeker seeker(target);
-    seeker.named = true;
     seeker.walk(tree);
     return seeker.found > 0;
   }
@@ -169,7 +170,6 @@ struct BranchSeeker : public PostWalker<BranchSeeker> {
   static Index countNamed(Expression* tree, Name target) {
     if (!target.is()) return 0;
     BranchSeeker seeker(target);
-    seeker.named = true;
     seeker.walk(tree);
     return seeker.found;
   }