add a drop for final elements in blocks if they are not used

9 files changed, 203 insertions, 125 deletions

diff --git a/src/ast_utils.h b/src/ast_utils.h
index 30e1d9a36..ea27c640f 100644
--- a/src/ast_utils.h
+++ b/src/ast_utils.h
@@ -789,7 +789,7 @@ struct ExpressionAnalyzer {
 
 // Adds drop() operations where necessary. This lets you not worry about adding drop when
 // generating code.
-struct AutoDrop : public WalkerPass<PostWalker<AutoDrop, Visitor<AutoDrop>>> {
+struct AutoDrop : public WalkerPass<ExpressionStackWalker<AutoDrop, Visitor<AutoDrop>>> {
   bool isFunctionParallel() override { return true; }
 
   Pass* create() override { return new AutoDrop; }
@@ -802,6 +802,12 @@ struct AutoDrop : public WalkerPass<PostWalker<AutoDrop, Visitor<AutoDrop>>> {
         curr->list[i] = Builder(*getModule()).makeDrop(child);
       }
     }
+    auto* last = curr->list.back();
+    expressionStack.push_back(last);
+    if (isConcreteWasmType(last->type) && !ExpressionAnalyzer::isResultUsed(expressionStack, getFunction())) {
+      curr->list.back() = Builder(*getModule()).makeDrop(last);
+    }
+    expressionStack.pop_back();
   }
 
   void visitFunction(Function* curr) {
diff --git a/test/emcc_hello_world.fromasm b/test/emcc_hello_world.fromasm
index 78c577bbf..ea3485584 100644
--- a/test/emcc_hello_world.fromasm
+++ b/test/emcc_hello_world.fromasm
@@ -7290,10 +7290,12 @@
                                     (i32.const 0)
                                   )
                                 )
-                                (call $___fwritex
-                                  (i32.const 4143)
-                                  (i32.const 1)
-                                  (get_local $0)
+                                (drop
+                                  (call $___fwritex
+                                    (i32.const 4143)
+                                    (i32.const 1)
+                                    (get_local $0)
+                                  )
                                 )
                               )
                             )
@@ -7519,10 +7521,12 @@
                                           )
                                           (br $do-once$122)
                                         )
-                                        (call $___fwritex
-                                          (i32.const 4143)
-                                          (i32.const 1)
-                                          (get_local $0)
+                                        (drop
+                                          (call $___fwritex
+                                            (i32.const 4143)
+                                            (i32.const 1)
+                                            (get_local $0)
+                                          )
                                         )
                                       )
                                       (block
@@ -7645,13 +7649,15 @@
                               (i32.const 0)
                             )
                           )
-                          (call $___fwritex
-                            (get_local $13)
-                            (i32.sub
-                              (get_local $40)
+                          (drop
+                            (call $___fwritex
                               (get_local $13)
+                              (i32.sub
+                                (get_local $40)
+                                (get_local $13)
+                              )
+                              (get_local $0)
                             )
-                            (get_local $0)
                           )
                         )
                       )
@@ -9446,10 +9452,12 @@
               (br $do-once$0)
             )
           )
-          (call $___fwritex
-            (get_local $6)
-            (get_local $1)
-            (get_local $0)
+          (drop
+            (call $___fwritex
+              (get_local $6)
+              (get_local $1)
+              (get_local $0)
+            )
           )
         )
       )
diff --git a/test/emcc_hello_world.fromasm.imprecise b/test/emcc_hello_world.fromasm.imprecise
index d6c27e3c4..06efe55d2 100644
--- a/test/emcc_hello_world.fromasm.imprecise
+++ b/test/emcc_hello_world.fromasm.imprecise
@@ -7284,10 +7284,12 @@
                                     (i32.const 0)
                                   )
                                 )
-                                (call $___fwritex
-                                  (i32.const 4143)
-                                  (i32.const 1)
-                                  (get_local $0)
+                                (drop
+                                  (call $___fwritex
+                                    (i32.const 4143)
+                                    (i32.const 1)
+                                    (get_local $0)
+                                  )
                                 )
                               )
                             )
@@ -7513,10 +7515,12 @@
                                           )
                                           (br $do-once$122)
                                         )
-                                        (call $___fwritex
-                                          (i32.const 4143)
-                                          (i32.const 1)
-                                          (get_local $0)
+                                        (drop
+                                          (call $___fwritex
+                                            (i32.const 4143)
+                                            (i32.const 1)
+                                            (get_local $0)
+                                          )
                                         )
                                       )
                                       (block
@@ -7639,13 +7643,15 @@
                               (i32.const 0)
                             )
                           )
-                          (call $___fwritex
-                            (get_local $13)
-                            (i32.sub
-                              (get_local $40)
+                          (drop
+                            (call $___fwritex
                               (get_local $13)
+                              (i32.sub
+                                (get_local $40)
+                                (get_local $13)
+                              )
+                              (get_local $0)
                             )
-                            (get_local $0)
                           )
                         )
                       )
@@ -9440,10 +9446,12 @@
               (br $do-once$0)
             )
           )
-          (call $___fwritex
-            (get_local $6)
-            (get_local $1)
-            (get_local $0)
+          (drop
+            (call $___fwritex
+              (get_local $6)
+              (get_local $1)
+              (get_local $0)
+            )
           )
         )
       )
diff --git a/test/emcc_hello_world.fromasm.imprecise.no-opts b/test/emcc_hello_world.fromasm.imprecise.no-opts
index 298b05867..5e469d9bb 100644
--- a/test/emcc_hello_world.fromasm.imprecise.no-opts
+++ b/test/emcc_hello_world.fromasm.imprecise.no-opts
@@ -4670,16 +4670,18 @@
                 (get_local $$sub$ptr$rhs$cast)
               )
             )
-            (call_indirect $FUNCSIG$iiii
-              (get_local $$f)
-              (get_local $$sub$ptr$sub)
-              (i32.const 1)
-              (i32.add
-                (i32.and
-                  (get_local $$6)
-                  (i32.const 7)
+            (drop
+              (call_indirect $FUNCSIG$iiii
+                (get_local $$f)
+                (get_local $$sub$ptr$sub)
+                (i32.const 1)
+                (i32.add
+                  (i32.and
+                    (get_local $$6)
+                    (i32.const 7)
+                  )
+                  (i32.const 2)
                 )
-                (i32.const 2)
               )
             )
           )
@@ -12421,10 +12423,12 @@
                                           (get_local $$sub$ptr$rhs$cast695$i)
                                         )
                                       )
-                                      (call $___fwritex
-                                        (get_local $$s668$1$i)
-                                        (get_local $$sub$ptr$sub696$i)
-                                        (get_local $$f)
+                                      (drop
+                                        (call $___fwritex
+                                          (get_local $$s668$1$i)
+                                          (get_local $$sub$ptr$sub696$i)
+                                          (get_local $$f)
+                                        )
                                       )
                                     )
                                   )
@@ -12490,10 +12494,12 @@
                                       )
                                       (br $do-once$114)
                                     )
-                                    (call $___fwritex
-                                      (i32.const 4143)
-                                      (i32.const 1)
-                                      (get_local $$f)
+                                    (drop
+                                      (call $___fwritex
+                                        (i32.const 4143)
+                                        (i32.const 1)
+                                        (get_local $$f)
+                                      )
                                     )
                                   )
                                 )
@@ -12622,10 +12628,12 @@
                                               (get_local $$p$addr$4489$i)
                                             )
                                           )
-                                          (call $___fwritex
-                                            (get_local $$s715$0$lcssa$i)
-                                            (get_local $$cond732$i)
-                                            (get_local $$f)
+                                          (drop
+                                            (call $___fwritex
+                                              (get_local $$s715$0$lcssa$i)
+                                              (get_local $$cond732$i)
+                                              (get_local $$f)
+                                            )
                                           )
                                         )
                                       )
@@ -12966,10 +12974,12 @@
                                               (get_local $$p$addr$5501$i)
                                             )
                                           )
-                                          (call $___fwritex
-                                            (get_local $$s753$2$i)
-                                            (get_local $$cond800$i)
-                                            (get_local $$f)
+                                          (drop
+                                            (call $___fwritex
+                                              (get_local $$s753$2$i)
+                                              (get_local $$cond800$i)
+                                              (get_local $$f)
+                                            )
                                           )
                                         )
                                       )
@@ -13073,10 +13083,12 @@
                                   (get_local $$sub$ptr$rhs$cast812$i)
                                 )
                               )
-                              (call $___fwritex
-                                (get_local $$estr$2$i)
-                                (get_local $$sub$ptr$sub813$i)
-                                (get_local $$f)
+                              (drop
+                                (call $___fwritex
+                                  (get_local $$estr$2$i)
+                                  (get_local $$sub$ptr$sub813$i)
+                                  (get_local $$f)
+                                )
                               )
                             )
                           )
@@ -16443,10 +16455,12 @@
               (br $do-once$0)
             )
           )
-          (call $___fwritex
-            (get_local $$pad)
-            (get_local $$l$addr$0$lcssa21)
-            (get_local $$f)
+          (drop
+            (call $___fwritex
+              (get_local $$pad)
+              (get_local $$l$addr$0$lcssa21)
+              (get_local $$f)
+            )
           )
         )
       )
diff --git a/test/emcc_hello_world.fromasm.no-opts b/test/emcc_hello_world.fromasm.no-opts
index 28e44d8f0..d1295a8bd 100644
--- a/test/emcc_hello_world.fromasm.no-opts
+++ b/test/emcc_hello_world.fromasm.no-opts
@@ -4676,16 +4676,18 @@
                 (get_local $$sub$ptr$rhs$cast)
               )
             )
-            (call_indirect $FUNCSIG$iiii
-              (get_local $$f)
-              (get_local $$sub$ptr$sub)
-              (i32.const 1)
-              (i32.add
-                (i32.and
-                  (get_local $$6)
-                  (i32.const 7)
+            (drop
+              (call_indirect $FUNCSIG$iiii
+                (get_local $$f)
+                (get_local $$sub$ptr$sub)
+                (i32.const 1)
+                (i32.add
+                  (i32.and
+                    (get_local $$6)
+                    (i32.const 7)
+                  )
+                  (i32.const 2)
                 )
-                (i32.const 2)
               )
             )
           )
@@ -12427,10 +12429,12 @@
                                           (get_local $$sub$ptr$rhs$cast695$i)
                                         )
                                       )
-                                      (call $___fwritex
-                                        (get_local $$s668$1$i)
-                                        (get_local $$sub$ptr$sub696$i)
-                                        (get_local $$f)
+                                      (drop
+                                        (call $___fwritex
+                                          (get_local $$s668$1$i)
+                                          (get_local $$sub$ptr$sub696$i)
+                                          (get_local $$f)
+                                        )
                                       )
                                     )
                                   )
@@ -12496,10 +12500,12 @@
                                       )
                                       (br $do-once$114)
                                     )
-                                    (call $___fwritex
-                                      (i32.const 4143)
-                                      (i32.const 1)
-                                      (get_local $$f)
+                                    (drop
+                                      (call $___fwritex
+                                        (i32.const 4143)
+                                        (i32.const 1)
+                                        (get_local $$f)
+                                      )
                                     )
                                   )
                                 )
@@ -12628,10 +12634,12 @@
                                               (get_local $$p$addr$4489$i)
                                             )
                                           )
-                                          (call $___fwritex
-                                            (get_local $$s715$0$lcssa$i)
-                                            (get_local $$cond732$i)
-                                            (get_local $$f)
+                                          (drop
+                                            (call $___fwritex
+                                              (get_local $$s715$0$lcssa$i)
+                                              (get_local $$cond732$i)
+                                              (get_local $$f)
+                                            )
                                           )
                                         )
                                       )
@@ -12972,10 +12980,12 @@
                                               (get_local $$p$addr$5501$i)
                                             )
                                           )
-                                          (call $___fwritex
-                                            (get_local $$s753$2$i)
-                                            (get_local $$cond800$i)
-                                            (get_local $$f)
+                                          (drop
+                                            (call $___fwritex
+                                              (get_local $$s753$2$i)
+                                              (get_local $$cond800$i)
+                                              (get_local $$f)
+                                            )
                                           )
                                         )
                                       )
@@ -13079,10 +13089,12 @@
                                   (get_local $$sub$ptr$rhs$cast812$i)
                                 )
                               )
-                              (call $___fwritex
-                                (get_local $$estr$2$i)
-                                (get_local $$sub$ptr$sub813$i)
-                                (get_local $$f)
+                              (drop
+                                (call $___fwritex
+                                  (get_local $$estr$2$i)
+                                  (get_local $$sub$ptr$sub813$i)
+                                  (get_local $$f)
+                                )
                               )
                             )
                           )
@@ -16449,10 +16461,12 @@
               (br $do-once$0)
             )
           )
-          (call $___fwritex
-            (get_local $$pad)
-            (get_local $$l$addr$0$lcssa21)
-            (get_local $$f)
+          (drop
+            (call $___fwritex
+              (get_local $$pad)
+              (get_local $$l$addr$0$lcssa21)
+              (get_local $$f)
+            )
           )
         )
       )
diff --git a/test/min.fromasm.imprecise.no-opts b/test/min.fromasm.imprecise.no-opts
index 9b9d6a353..bde70a203 100644
--- a/test/min.fromasm.imprecise.no-opts
+++ b/test/min.fromasm.imprecise.no-opts
@@ -45,8 +45,10 @@
             )
           )
         )
-        (i32.reinterpret/f32
-          (get_local $f)
+        (drop
+          (i32.reinterpret/f32
+            (get_local $f)
+          )
         )
       )
     )
diff --git a/test/min.fromasm.no-opts b/test/min.fromasm.no-opts
index 9b9d6a353..bde70a203 100644
--- a/test/min.fromasm.no-opts
+++ b/test/min.fromasm.no-opts
@@ -45,8 +45,10 @@
             )
           )
         )
-        (i32.reinterpret/f32
-          (get_local $f)
+        (drop
+          (i32.reinterpret/f32
+            (get_local $f)
+          )
         )
       )
     )
diff --git a/test/unit.fromasm.imprecise.no-opts b/test/unit.fromasm.imprecise.no-opts
index 65f556365..05e93926b 100644
--- a/test/unit.fromasm.imprecise.no-opts
+++ b/test/unit.fromasm.imprecise.no-opts
@@ -371,7 +371,9 @@
         (drop
           (f32.const 5)
         )
-        (f32.const 0)
+        (drop
+          (f32.const 0)
+        )
       )
     )
   )
@@ -611,9 +613,11 @@
             (get_local $f)
           )
         )
-        (i32.reinterpret/f32
-          (f32.demote/f64
-            (get_local $d)
+        (drop
+          (i32.reinterpret/f32
+            (f32.demote/f64
+              (get_local $d)
+            )
           )
         )
       )
@@ -646,10 +650,14 @@
                       (drop
                         (i32.const 4)
                       )
-                      (i32.const 5)
+                      (drop
+                        (i32.const 5)
+                      )
                     )
                   )
-                  (i32.const 6)
+                  (drop
+                    (i32.const 6)
+                  )
                 )
               )
               (i32.const 7)
@@ -712,13 +720,17 @@
                         (i32.const 4)
                       )
                     )
-                    (call $lb
-                      (i32.const 5)
+                    (drop
+                      (call $lb
+                        (i32.const 5)
+                      )
                     )
                   )
                 )
-                (call $lb
-                  (i32.const 6)
+                (drop
+                  (call $lb
+                    (i32.const 6)
+                  )
                 )
               )
             )
diff --git a/test/unit.fromasm.no-opts b/test/unit.fromasm.no-opts
index a170b7676..ae894c99e 100644
--- a/test/unit.fromasm.no-opts
+++ b/test/unit.fromasm.no-opts
@@ -377,7 +377,9 @@
         (drop
           (f32.const 5)
         )
-        (f32.const 0)
+        (drop
+          (f32.const 0)
+        )
       )
     )
   )
@@ -617,9 +619,11 @@
             (get_local $f)
           )
         )
-        (i32.reinterpret/f32
-          (f32.demote/f64
-            (get_local $d)
+        (drop
+          (i32.reinterpret/f32
+            (f32.demote/f64
+              (get_local $d)
+            )
           )
         )
       )
@@ -652,10 +656,14 @@
                       (drop
                         (i32.const 4)
                       )
-                      (i32.const 5)
+                      (drop
+                        (i32.const 5)
+                      )
                     )
                   )
-                  (i32.const 6)
+                  (drop
+                    (i32.const 6)
+                  )
                 )
               )
               (i32.const 7)
@@ -718,13 +726,17 @@
                         (i32.const 4)
                       )
                     )
-                    (call $lb
-                      (i32.const 5)
+                    (drop
+                      (call $lb
+                        (i32.const 5)
+                      )
                     )
                   )
                 )
-                (call $lb
-                  (i32.const 6)
+                (drop
+                  (call $lb
+                    (i32.const 6)
+                  )
                 )
               )
             )