quickly avoid all unreachable branching in ifs

kripken · kripken · commit fe618683f2c8 · 2017-08-25T16:04:36.000-07:00
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
@@ -173,6 +173,11 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> {
     auto* iff = (*currp)->dynCast<If>();
 
     if (iff) {
+      if (iff->condition->type == unreachable) {
+        // avoid all the branching, we never reach it anyhow
+        *currp = iff->condition;
+        return;
+      }
       self->pushTask(doVisitIf, currp);
       if (iff->ifFalse) {
       // we need to join up if-else control flow, and clear after the condition
diff --git a/test/passes/remove-unused-brs.txt b/test/passes/remove-unused-brs.txt
@@ -1062,12 +1062,13 @@
  )
  (func $unreachable-if-that-could-be-a-br_if (type $7) (result i64)
   (loop $label$3
-   (if
-    (unreachable)
-    (f64.const 1)
-    (br $label$3)
-   )
+   (unreachable)
    (i64.const 1)
   )
  )
+ (func $nop-br-might-update-type (type $1)
+  (block $label$39
+   (unreachable)
+  )
+ )
 )
diff --git a/test/passes/remove-unused-brs.wast b/test/passes/remove-unused-brs.wast
@@ -953,5 +953,18 @@
     (i64.const 1)
    )
   )
+  (func $nop-br-might-update-type
+   (block $label$39
+    (if
+     (unreachable)
+     (if (result i32)
+      (i32.const 1)
+      (br $label$39) ;; if we nop this, then the parent type must change
+      (i32.const 0)
+     )
+     (i32.const 0)
+    )
+   )
+  )
 )
 

Original file line number	Diff line number	Diff line change
`@@ -1062,12 +1062,13 @@`
`1062`	`1062`	`)`
`1063`	`1063`	`(func $unreachable-if-that-could-be-a-br_if (type $7) (result i64)`
`1064`	`1064`	`(loop $label$3`
`1065`		`- (if`
`1066`		`- (unreachable)`
`1067`		`- (f64.const 1)`
`1068`		`- (br $label$3)`
`1069`		`- )`
	`1065`	`+ (unreachable)`
`1070`	`1066`	`(i64.const 1)`
`1071`	`1067`	`)`
`1072`	`1068`	`)`
	`1069`	`+ (func $nop-br-might-update-type (type $1)`
	`1070`	`+ (block $label$39`
	`1071`	`+ (unreachable)`
	`1072`	`+ )`
	`1073`	`+ )`
`1073`	`1074`	`)`
Original file line number	Diff line number	Diff line change
`@@ -953,5 +953,18 @@`
`953`	`953`	`(i64.const 1)`
`954`	`954`	`)`
`955`	`955`	`)`
	`956`	`+ (func $nop-br-might-update-type`
	`957`	`+ (block $label$39`
	`958`	`+ (if`
	`959`	`+ (unreachable)`
	`960`	`+ (if (result i32)`
	`961`	`+ (i32.const 1)`
	`962`	`+ (br $label$39) ;; if we nop this, then the parent type must change`
	`963`	`+ (i32.const 0)`
	`964`	`+ )`
	`965`	`+ (i32.const 0)`
	`966`	`+ )`
	`967`	`+ )`
	`968`	`+ )`
`956`	`969`	`)`
`957`	`970`