fix coalesce-locals handling of set/tee local of an unreachable; we still need the value, as it may do things

Author: kripken

src/passes/CoalesceLocals.cpp

@@ -168,9 +168,13 @@ struct CoalesceLocals : public WalkerPass<CFGWalker<CoalesceLocals, Visitor<Coal
 
   static void doVisitSetLocal(CoalesceLocals* self, Expression** currp) {
     auto* curr = (*currp)->cast<SetLocal>();
-    // if in unreachable code, ignore
+    // if in unreachable code, we don't need the tee (but might need the value, if it has side effects)
     if (!self->currBasicBlock) {
-      *currp = Builder(*self->getModule()).replaceWithIdenticalType(curr);
+      if (curr->isTee()) {
+        *currp = curr->value;
+      } else {
+        *currp = Builder(*self->getModule()).makeDrop(curr->value);
+      }
       return;
     }
     self->currBasicBlock->contents.actions.emplace_back(Action::Set, curr->index, currp);

test/passes/coalesce-locals-learning.txt

@@ -108,11 +108,15 @@
   )
   (block $block
    (br $block)
-   (nop)
    (drop
     (i32.const 0)
    )
-   (nop)
+   (drop
+    (i32.const 0)
+   )
+   (drop
+    (i32.const -1)
+   )
   )
   (drop
    (get_local $0)

test/passes/coalesce-locals.txt

@@ -6,6 +6,7 @@
  (type $4 (func (param i32)))
  (type $FUNCSIG$i (func (result i32)))
  (type $FUNCSIG$vi (func (param i32)))
+ (type $7 (func (param i32) (result i32)))
  (import "env" "_emscripten_autodebug_i32" (func $_emscripten_autodebug_i32 (param i32 i32) (result i32)))
  (import "env" "get" (func $get (result i32)))
  (import "env" "set" (func $set (param i32)))
@@ -112,11 +113,15 @@
   )
   (block $block
    (br $block)
-   (nop)
    (drop
     (i32.const 0)
    )
-   (nop)
+   (drop
+    (i32.const 0)
+   )
+   (drop
+    (i32.const -1)
+   )
   )
   (drop
    (get_local $0)
@@ -902,37 +907,53 @@
   (local $0 i32)
   (block $x
    (return)
-   (nop)
+   (drop
+    (i32.const 1)
+   )
+   (drop
+    (i32.const 0)
+   )
    (drop
     (i32.const 0)
    )
-   (nop)
   )
   (block $y
    (unreachable)
-   (nop)
+   (drop
+    (i32.const 1)
+   )
+   (drop
+    (i32.const 0)
+   )
    (drop
     (i32.const 0)
    )
-   (nop)
   )
   (block $z
    (br $z)
-   (nop)
+   (drop
+    (i32.const 1)
+   )
+   (drop
+    (i32.const 0)
+   )
    (drop
     (i32.const 0)
    )
-   (nop)
   )
   (block $z14
    (br_table $z14 $z14
     (i32.const 100)
    )
-   (nop)
+   (drop
+    (i32.const 1)
+   )
+   (drop
+    (i32.const 0)
+   )
    (drop
     (i32.const 0)
    )
-   (nop)
   )
  )
  (func $nop-in-unreachable (type $2)
@@ -1083,4 +1104,12 @@
    (br $top)
   )
  )
+ (func $tee_br (type $7) (param $0 i32) (result i32)
+  (block $b
+   (return
+    (br $b)
+   )
+  )
+  (i32.const 1)
+ )
 )

test/passes/coalesce-locals.wast

@@ -1075,4 +1075,14 @@
       (br $top)
     )
   )
+  (func $tee_br (param $x i32) (result i32)
+    (block $b
+      (return
+        (tee_local $x
+          (br $b)
+        )
+      )
+    )
+    (i32.const 1)
+  )
 )