Add support for trapsNeverHappen

Author: stevenfontanella

src/passes/DeadStoreElimination.cpp

@@ -139,7 +139,8 @@ struct Logic {
     //       after a trap) then we could stop assuming any trap can lead to
     //       access of global data, likely greatly reducing the number of
     //       barriers.
-    return currEffects.calls || currEffects.throws() || currEffects.trap ||
+    return currEffects.calls || currEffects.throws() ||
+           (!currEffects.trapsNeverHappen && currEffects.trap) ||
            currEffects.branchesOut;
   };
 

test/lit/passes/ldse-tnh.wast

@@ -0,0 +1,78 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; (--remove-unused-names avoids names on blocks, which would hamper the
+;; work in getFallthrough, as a name implies possible breaks)
+;; RUN: wasm-opt %s --traps-never-happen -all --remove-unused-names --ldse -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (type $A (struct (field (mut i32))))
+ (type $A (struct (field (mut i32))))
+
+ ;; CHECK:      (global $global$0 (mut i32) (i32.const 0))
+ (global $global$0 (mut i32) (i32.const 0))
+
+ ;; CHECK:      (func $simple-reaching-trap (type $0)
+ ;; CHECK-NEXT:  (local $x (ref null $A))
+ ;; CHECK-NEXT:  (block
+ ;; CHECK-NEXT:   (drop
+ ;; CHECK-NEXT:    (local.get $x)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (drop
+ ;; CHECK-NEXT:    (i32.const 10)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (block
+ ;; CHECK-NEXT:   (drop
+ ;; CHECK-NEXT:    (local.get $x)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:   (drop
+ ;; CHECK-NEXT:    (i32.const 20)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (unreachable)
+ ;; CHECK-NEXT: )
+ (func $simple-reaching-trap
+  (local $x (ref null $A))
+  (struct.set $A 0
+   (local.get $x)
+   (i32.const 10)
+  )
+  ;; a store reaching a trap may be observable from the outside later
+  (struct.set $A 0
+   (local.get $x)
+   (i32.const 20)
+  )
+  (unreachable)
+ )
+
+ ;; CHECK:      (func $global-trap (type $0)
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (i32.const 10)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (if
+ ;; CHECK-NEXT:   (i32.const 1)
+ ;; CHECK-NEXT:   (then
+ ;; CHECK-NEXT:    (unreachable)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (global.set $global$0
+ ;; CHECK-NEXT:   (i32.const 20)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $global-trap
+  (global.set $global$0
+   (i32.const 10)
+  )
+
+  ;; Conditional trap ignored when trapsNeverHappen.
+  (if
+   (i32.const 1)
+   (then
+    (unreachable)
+   )
+  )
+  (global.set $global$0
+   (i32.const 20)
+  )
+ )
+
+)

test/lit/passes/ldse.wast

@@ -12,8 +12,6 @@
  (type $B (struct (field (mut f64))))
  (type $C (struct (field (mut i32)) (field (mut i32))))
 
- (memory 10 10 shared)
-
  ;; CHECK:      (global $global$0 (mut i32) (i32.const 0))
  (global $global$0 (mut i32) (i32.const 0))
  ;; CHECK:      (global $global$1 (mut i32) (i32.const 0))