fix ssaify bug where we failed to update the location of values as we…

… moved them around, causing us to zero out the wrong thing in another place and ensuing hilarity (#1212)

src/ast/LocalGraph.cpp

@@ -17,13 +17,26 @@
 #include <iterator>
 
 #include <wasm-builder.h>
+#include <wasm-printing.h>
 #include <ast/find_all.h>
 #include <ast/local-graph.h>
 
 namespace wasm {
 
 LocalGraph::LocalGraph(Function* func, Module* module) {
   walkFunctionInModule(func, module);
+
+#ifdef LOCAL_GRAPH_DEBUG
+  std::cout << "LocalGraph::dump\n";
+  for (auto& pair : getSetses) {
+    auto* get = pair.first;
+    auto& sets = pair.second;
+    std::cout << "GET\n" << get << " is influenced by\n";
+    for (auto* set : sets) {
+      std::cout << set << '\n';
+    }
+  }
+#endif
 }
 
 void LocalGraph::computeInfluences() {

src/passes/SSAify.cpp

@@ -60,7 +60,7 @@ struct SSAify : public Pass {
     LocalGraph graph(func, module);
     // create new local indexes, one for each set
     createNewIndexes(graph);
-    // we now know the sets for each get
+    // we now know the sets for each get, and can compute get indexes and handle phis
     computeGetsAndPhis(graph);
     // add prepends to function
     addPrepends();
@@ -75,7 +75,6 @@ struct SSAify : public Pass {
     }
   }
 
-  // After we traversed it all, we can compute gets and phis
   void computeGetsAndPhis(LocalGraph& graph) {
     for (auto& iter : graph.getSetses) {
       auto* get = iter.first;
@@ -84,8 +83,7 @@ struct SSAify : public Pass {
         continue; // unreachable, ignore
       }
       if (sets.size() == 1) {
-        // TODO: add tests for this case
-        // easy, just one set, use it's index
+        // easy, just one set, use its index
         auto* set = *sets.begin();
         if (set) {
           get->index = set->index;
@@ -138,10 +136,18 @@ struct SSAify : public Pass {
         for (auto* set : sets) {
           if (set) {
             // a set exists, just add a tee of its value
-            set->value = builder.makeTeeLocal(
+            auto* value = set->value;
+            auto* tee = builder.makeTeeLocal(
               new_,
-              set->value
+              value
             );
+            set->value = tee;
+            // the value may have been something we tracked the location
+            // of. if so, update that, since we moved it into the tee
+            if (graph.locations.count(value) > 0) {
+              assert(graph.locations[value] == &set->value);
+              graph.locations[value] = &tee->value;
+            }
           } else {
             // this is a param or the zero init value.
             if (func->isParam(old)) {

test/passes/ssa.txt

@@ -1,6 +1,8 @@
 (module
  (type $0 (func (param i32)))
  (type $1 (func))
+ (type $2 (func (result i32)))
+ (global $global$0 (mut i32) (i32.const 1))
  (memory $0 0)
  (func $basics (type $0) (param $x i32)
   (local $y i32)
@@ -691,4 +693,38 @@
    )
   )
  )
+ (func $func_6 (type $2) (result i32)
+  (local $result i32)
+  (local $zero i32)
+  (local $2 i32)
+  (local $3 i32)
+  (local $4 i32)
+  (loop $label$1
+   (if
+    (i32.eqz
+     (get_global $global$0)
+    )
+    (return
+     (get_local $4)
+    )
+   )
+   (set_global $global$0
+    (i32.const 0)
+   )
+   (set_local $2
+    (tee_local $4
+     (i32.const 1)
+    )
+   )
+   (br_if $label$1
+    (i32.const 0)
+   )
+   (set_local $3
+    (tee_local $4
+     (i32.const 0)
+    )
+   )
+   (br $label$1)
+  )
+ )
 )

test/passes/ssa.wast

@@ -1,4 +1,5 @@
 (module
+  (global $global$0 (mut i32) (i32.const 1))
   (func $basics (param $x i32)
     (local $y i32)
     (local $z f32)
@@ -311,5 +312,32 @@
     )
     (drop (get_local $x)) ;; can receive from either set, or input param
   )
+  (func $func_6 (result i32)
+   (local $result i32)
+   (local $zero i32)
+   (loop $label$1
+    (if
+     (i32.eqz
+      (get_global $global$0)
+     )
+     (return
+      (get_local $result) ;; we eventually reach here
+     )
+    )
+    (set_global $global$0
+     (i32.const 0) ;; tell next iteration to return
+    )
+    (set_local $result
+     (i32.const 1) ;; set the return value to 1, temporarily
+    )
+    (br_if $label$1
+     (i32.const 0) ;; don't do anything here
+    )
+    (set_local $result
+     (get_local $zero) ;; set it to zero instead
+    )
+    (br $label$1) ;; back to the top, where we will return the zero
+   )
+  )
 )