MergeBlocks: Optimize all dropped blocks (WebAssembly#6984)

Just call optimizeDroppedBlock from visitDrop to handle that. Followup to WebAssembly#6982. This optimizes the new testcase added there. Some older tests also improve.
aheejin · Oct 4, 2024 · 0be8d5e · 0be8d5e
1 parent cbad8ec
commit 0be8d5e
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Showing 7 changed files with 76 additions and 82 deletions.
diff --git a/src/passes/MergeBlocks.cpp b/src/passes/MergeBlocks.cpp
@@ -434,6 +434,15 @@ struct MergeBlocks
     optimizeBlock(curr, getModule(), getPassOptions(), branchInfo);
   }
 
+  void visitDrop(Drop* curr) {
+    if (auto* block = curr->value->dynCast<Block>()) {
+      if (optimizeDroppedBlock(
+            curr, block, *getModule(), getPassOptions(), branchInfo)) {
+        replaceCurrent(block);
+      }
+    }
+  }
+
   // given
   // (curr
   //  (block=child

diff --git a/test/lit/passes/merge-blocks.wast b/test/lit/passes/merge-blocks.wast
@@ -405,17 +405,16 @@
  )
 
  ;; CHECK:      (func $toplevel (type $4)
- ;; CHECK-NEXT:  (drop
- ;; CHECK-NEXT:   (block $label (result i32)
- ;; CHECK-NEXT:    (br $label
- ;; CHECK-NEXT:     (i32.const 42)
- ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:  (block $label
+ ;; CHECK-NEXT:   (drop
+ ;; CHECK-NEXT:    (i32.const 42)
  ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (br $label)
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )
  (func $toplevel
   ;; Test we can remove a block value even when the drop is at the toplevel of
-  ;; a function. This is not done yet TODO
+  ;; a function.
   (drop
    (block $label (result i32)
     (br $label

diff --git a/test/lit/passes/merge-blocks_names.wast b/test/lit/passes/merge-blocks_names.wast
@@ -0,0 +1,28 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --merge-blocks -all -S -o - | filecheck %s
+;;
+;; Similar to merge-blocks.wast, but without --remove-unused-names. This tests
+;; the pass entirely by itself.
+
+(module
+ ;; CHECK:      (func $nested-dropped-blocks (type $0)
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (i32.const 42)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $nested-dropped-blocks
+  ;; Fully removing unneeded blocks here requires multiple operations to happen.
+  ;; Specifically, we remove all the outer blocks first, and only then get to
+  ;; the inner named block, which we can then infer is not needed either.
+  (block
+   (drop
+    (block (result i32)
+     (block $named (result i32)
+      (i32.const 42)
+     )
+    )
+   )
+  )
+ )
+)
+
diff --git a/test/lit/passes/monomorphize-drop.wast b/test/lit/passes/monomorphize-drop.wast
@@ -672,12 +672,7 @@
 
 ;; CAREFUL:      (func $return-normal_4 (type $1)
 ;; CAREFUL-NEXT:  (drop
-;; CAREFUL-NEXT:   (block
-;; CAREFUL-NEXT:    (drop
-;; CAREFUL-NEXT:     (call $import)
-;; CAREFUL-NEXT:    )
-;; CAREFUL-NEXT:    (return)
-;; CAREFUL-NEXT:   )
+;; CAREFUL-NEXT:   (call $import)
 ;; CAREFUL-NEXT:  )
 ;; CAREFUL-NEXT: )
 

diff --git a/test/passes/Oz_fuzz-exec_all-features.txt b/test/passes/Oz_fuzz-exec_all-features.txt
@@ -183,14 +183,10 @@
   (nop)
  )
  (func $br-on_non_null-2 (type $void_func)
-  (drop
-   (block
-    (call $log
-     (i32.const 1)
-    )
-    (unreachable)
-   )
+  (call $log
+   (i32.const 1)
   )
+  (unreachable)
  )
  (func $cast-on-func (type $void_func)
   (call $log

diff --git a/test/passes/merge-blocks.txt b/test/passes/merge-blocks.txt
@@ -10,11 +10,12 @@
   )
  )
  (func $drop-block-br
-  (drop
-   (block $x (result i32)
-    (br $x
-     (i32.const 1)
-    )
+  (block $x
+   (drop
+    (i32.const 1)
+   )
+   (br $x)
+   (drop
     (i32.const 0)
    )
   )
@@ -77,15 +78,9 @@
   )
  )
  (func $drop-block-squared-iloop
-  (drop
-   (block $label$0 (result i32)
-    (drop
-     (block $label$1
-      (loop $label$2
-       (br $label$2)
-      )
-     )
-    )
+  (block $label$0
+   (loop $label$2
+    (br $label$2)
    )
   )
  )
@@ -109,11 +104,7 @@
  (func $loop-block-drop-block-return
   (loop $label$4
    (block $label$5
-    (drop
-     (block $label$6 (result i32)
-      (return)
-     )
-    )
+    (return)
    )
   )
  )

diff --git a/test/passes/remove-unused-names_merge-blocks_all-features.txt b/test/passes/remove-unused-names_merge-blocks_all-features.txt
@@ -286,15 +286,11 @@
    (i32.const 30)
   )
   (drop
-   (block
-    (drop
-     (i32.const 10)
-    )
-    (i32.add
-     (unreachable)
-     (i32.const 20)
-    )
-   )
+   (i32.const 10)
+  )
+  (i32.add
+   (unreachable)
+   (i32.const 20)
   )
   (drop
    (i32.const 20)
@@ -822,40 +818,30 @@
  )
  (func $drop-unreachable (type $2) (result i32)
   (local $0 i32)
-  (drop
-   (block (result i32)
-    (unreachable)
-   )
-  )
+  (unreachable)
   (unreachable)
  )
  (func $concrete_finale_in_unreachable (type $5) (result f64)
-  (drop
-   (block (result f64)
-    (unreachable)
+  (block
+   (unreachable)
+   (drop
     (f64.const 6.322092475576799e-96)
    )
   )
   (f64.const -1)
  )
  (func $dont-move-unreachable (type $3)
   (loop $label$0
+   (br $label$0)
    (drop
-    (block (result i32)
-     (br $label$0)
-     (i32.const 1)
-    )
+    (i32.const 1)
    )
   )
  )
  (func $dont-move-unreachable-last (type $3)
   (loop $label$0
-   (drop
-    (block (result i32)
-     (call $dont-move-unreachable-last)
-     (br $label$0)
-    )
-   )
+   (call $dont-move-unreachable-last)
+   (br $label$0)
   )
  )
  (func $move-around-unreachable-in-middle (type $3)
@@ -876,16 +862,10 @@
  )
  (func $drop-unreachable-block-with-concrete-final (type $3)
   (drop
-   (block (result i32)
-    (drop
-     (block
-      (drop
-       (return)
-      )
-     )
-    )
-    (i32.const -452)
-   )
+   (return)
+  )
+  (drop
+   (i32.const -452)
   )
  )
  (func $merging-with-unreachable-in-middle (type $2) (result i32)
@@ -901,13 +881,9 @@
  )
  (func $remove-br-after-unreachable (type $3)
   (block $label$9
-   (drop
-    (block
-     (block
-      (return)
-      (br $label$9)
-     )
-    )
+   (block
+    (return)
+    (br $label$9)
    )
   )
  )