Effects: Differentiate mutable from immutable globals (#4286)

Similar to what we do with structs, if a global is immutable then we know it
cannot interact with calls.

This changes the JS API for getSideEffects(). That was actually broken,
as passing in the optional module param would just pass it along to the
compiled C code, so it was coerced to 0 or 1, and not a pointer to a module.
To fix that, this now does module.ptr to actually get the pointer, and this is
now actually tested as without a module we cannot compute the effects of a
global. This PR also makes the module param mandatory in the JS API,
as again, without a module we can't compute global effects. (The module
param has already been mandatory in the C++ API for some time.)

1 files changed, 51 insertions, 0 deletions

diff --git a/test/lit/passes/simplify-locals-global.wast b/test/lit/passes/simplify-locals-global.wast
new file mode 100644
index 000000000..215b32a3c
--- /dev/null
+++ b/test/lit/passes/simplify-locals-global.wast
@@ -0,0 +1,51 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+;; RUN: wasm-opt %s --simplify-locals -S -o - | filecheck %s
+
+(module
+  ;; CHECK:      (global $imm-glob i32 (i32.const 1234))
+  (global $imm-glob i32 (i32.const 1234))
+
+  ;; CHECK:      (global $mut-glob (mut i32) (i32.const 5678))
+  (global $mut-glob (mut i32) (i32.const 5678))
+
+  ;; CHECK:      (func $reorder-of-immmutable-global (result i32)
+  ;; CHECK-NEXT:  (local $temp i32)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT:  (call $helper)
+  ;; CHECK-NEXT:  (global.get $imm-glob)
+  ;; CHECK-NEXT: )
+  (func $reorder-of-immmutable-global (result i32)
+    (local $temp i32)
+    ;; As the global is immutable, it cannot be modified in the call, and we can
+    ;; reorder here.
+    (local.set $temp
+      (global.get $imm-glob)
+    )
+    (call $helper)
+    (local.get $temp)
+  )
+
+  ;; CHECK:      (func $no-reorder-of-mutable-global (result i32)
+  ;; CHECK-NEXT:  (local $temp i32)
+  ;; CHECK-NEXT:  (local.set $temp
+  ;; CHECK-NEXT:   (global.get $mut-glob)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (call $helper)
+  ;; CHECK-NEXT:  (local.get $temp)
+  ;; CHECK-NEXT: )
+  (func $no-reorder-of-mutable-global (result i32)
+    (local $temp i32)
+    ;; As the global is mutable, it can be modified in the call, and we cannot
+    ;; reorder here.
+    (local.set $temp
+      (global.get $mut-glob)
+    )
+    (call $helper)
+    (local.get $temp)
+  )
+
+  ;; CHECK:      (func $helper
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $helper)
+)