Compile incrementors in for loops within the initializer's flow

It turns out that incrementors were compiled with the body's flow, which
meant that the incrementor had access to local variables declared in the
body. Now, incrementors no longer have access to such variables.

Fixes AssemblyScript#2825.

src/compiler.ts

@@ -2600,6 +2600,7 @@ export class Compiler extends DiagnosticEmitter {
     if (possiblyLoops) {
       let incrementor = statement.incrementor;
       if (incrementor) {
+        this.currentFlow = flow;
         bodyStmts.push(
           this.compileExpression(incrementor, Type.void, Constraints.ConvImplicit | Constraints.WillDrop)
         );

tests/compiler/issues/2825.debug.wat

@@ -0,0 +1,55 @@
+(module
+ (type $0 (func))
+ (type $1 (func (param i32 i32 i32 i32)))
+ (type $2 (func (param i32) (result i32)))
+ (import "env" "abort" (func $~lib/builtins/abort (param i32 i32 i32 i32)))
+ (global $~lib/memory/__data_end i32 (i32.const 60))
+ (global $~lib/memory/__stack_pointer (mut i32) (i32.const 32828))
+ (global $~lib/memory/__heap_base i32 (i32.const 32828))
+ (memory $0 1)
+ (data $0 (i32.const 12) ",\00\00\00\00\00\00\00\00\00\00\00\02\00\00\00\1c\00\00\00i\00s\00s\00u\00e\00s\00/\002\008\002\005\00.\00t\00s\00")
+ (table $0 1 1 funcref)
+ (elem $0 (i32.const 1))
+ (export "memory" (memory $0))
+ (start $~start)
+ (func $issues/2825/increment (param $x i32) (result i32)
+  local.get $x
+  i32.const 1234
+  i32.ne
+  i32.eqz
+  if
+   i32.const 0
+   i32.const 32
+   i32.const 2
+   i32.const 3
+   call $~lib/builtins/abort
+   unreachable
+  end
+  local.get $x
+  i32.const 1
+  i32.add
+  return
+ )
+ (func $start:issues/2825
+  (local $i i32)
+  (local $i|1 i32)
+  i32.const 0
+  local.set $i
+  loop $for-loop|0
+   local.get $i
+   i32.const 10
+   i32.lt_s
+   if
+    i32.const 1234
+    local.set $i|1
+    local.get $i
+    call $issues/2825/increment
+    local.set $i
+    br $for-loop|0
+   end
+  end
+ )
+ (func $~start
+  call $start:issues/2825
+ )
+)

tests/compiler/issues/2825.json

@@ -0,0 +1 @@
+{}

tests/compiler/issues/2825.release.wat

@@ -0,0 +1,36 @@
+(module
+ (type $0 (func (param i32 i32 i32 i32)))
+ (type $1 (func))
+ (import "env" "abort" (func $~lib/builtins/abort (param i32 i32 i32 i32)))
+ (memory $0 1)
+ (data $0 (i32.const 1036) ",")
+ (data $0.1 (i32.const 1048) "\02\00\00\00\1c\00\00\00i\00s\00s\00u\00e\00s\00/\002\008\002\005\00.\00t\00s")
+ (export "memory" (memory $0))
+ (start $~start)
+ (func $~start
+  (local $0 i32)
+  loop $for-loop|0
+   local.get $0
+   i32.const 10
+   i32.lt_s
+   if
+    local.get $0
+    i32.const 1234
+    i32.eq
+    if
+     i32.const 0
+     i32.const 1056
+     i32.const 2
+     i32.const 3
+     call $~lib/builtins/abort
+     unreachable
+    end
+    local.get $0
+    i32.const 1
+    i32.add
+    local.set $0
+    br $for-loop|0
+   end
+  end
+ )
+)

tests/compiler/issues/2825.ts

@@ -0,0 +1,8 @@
+function increment(x: i32): i32 {
+  assert(x !== 1234);
+  return x + 1;
+}
+
+for (let i = 0; i < 10; i = increment(i)) {
+  let i = 1234;
+}