[Strings] stringview_*.slice (#4805)

Unfortunately one slice is the same as python [start:end], using 2 params,
and the other slice is one param, [CURR:CURR+num] (where CURR is implied
by the current state in the iter). So we can't use a single class here. Perhaps
a different name would be good, like slice vs substring (like JS does), but
I picked names to match the current spec.

4 files changed, 27 insertions, 1 deletions

diff --git a/src/ir/ReFinalize.cpp b/src/ir/ReFinalize.cpp
index 2c3b6c1f0..771553e11 100644
--- a/src/ir/ReFinalize.cpp
+++ b/src/ir/ReFinalize.cpp
@@ -185,6 +185,10 @@ void ReFinalize::visitStringWTF8Advance(StringWTF8Advance* curr) {
 void ReFinalize::visitStringWTF16Get(StringWTF16Get* curr) { curr->finalize(); }
 void ReFinalize::visitStringIterNext(StringIterNext* curr) { curr->finalize(); }
 void ReFinalize::visitStringIterMove(StringIterMove* curr) { curr->finalize(); }
+void ReFinalize::visitStringSliceWTF(StringSliceWTF* curr) { curr->finalize(); }
+void ReFinalize::visitStringSliceIter(StringSliceIter* curr) {
+  curr->finalize();
+}
 
 void ReFinalize::visitFunction(Function* curr) {
   // we may have changed the body from unreachable to none, which might be bad
diff --git a/src/ir/cost.h b/src/ir/cost.h
index 3ed37e297..8ebc6eb9b 100644
--- a/src/ir/cost.h
+++ b/src/ir/cost.h
@@ -672,7 +672,7 @@ struct CostAnalyzer : public OverriddenVisitor<CostAnalyzer, CostType> {
   }
   CostType visitRefAs(RefAs* curr) { return 1 + visit(curr->value); }
   CostType visitStringNew(StringNew* curr) {
-    return 4 + visit(curr->ptr) + visit(curr->length);
+    return 8 + visit(curr->ptr) + visit(curr->length);
   }
   CostType visitStringConst(StringConst* curr) { return 4; }
   CostType visitStringMeasure(StringMeasure* curr) {
@@ -701,6 +701,12 @@ struct CostAnalyzer : public OverriddenVisitor<CostAnalyzer, CostType> {
   CostType visitStringIterMove(StringIterMove* curr) {
     return 4 + visit(curr->ref) + visit(curr->num);
   }
+  CostType visitStringSliceWTF(StringSliceWTF* curr) {
+    return 8 + visit(curr->ref) + visit(curr->start) + visit(curr->end);
+  }
+  CostType visitStringSliceIter(StringSliceIter* curr) {
+    return 8 + visit(curr->ref) + visit(curr->num);
+  }
 
 private:
   CostType nullCheckCost(Expression* ref) {
diff --git a/src/ir/effects.h b/src/ir/effects.h
index 7045d9382..58480f0ff 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -777,6 +777,14 @@ private:
       parent.readsArray = true;
       parent.writesArray = true;
     }
+    void visitStringSliceWTF(StringSliceWTF* curr) {
+      // traps when ref is null.
+      parent.implicitTrap = true;
+    }
+    void visitStringSliceIter(StringSliceIter* curr) {
+      // traps when ref is null.
+      parent.implicitTrap = true;
+    }
   };
 
 public:
diff --git a/src/ir/possible-contents.cpp b/src/ir/possible-contents.cpp
index 35a855614..a0e64e236 100644
--- a/src/ir/possible-contents.cpp
+++ b/src/ir/possible-contents.cpp
@@ -717,6 +717,14 @@ struct InfoCollector
     // TODO: optimize when possible
     addRoot(curr);
   }
+  void visitStringSliceWTF(StringSliceWTF* curr) {
+    // TODO: optimize when possible
+    addRoot(curr);
+  }
+  void visitStringSliceIter(StringSliceIter* curr) {
+    // TODO: optimize when possible
+    addRoot(curr);
+  }
 
   // TODO: Model which throws can go to which catches. For now, anything thrown
   //       is sent to the location of that tag, and any catch of that tag can