[NFC-ish] Avoid repeated ReFinalize etc. when inlining (WebAssembly#6967

)

We may inline multiple times into a single function. Previously, if we did so, we
did the "fixups" such as ReFinalize and non-nullable local fixes once per such
inlining. But that is wasteful as each ReFinalize etc. scans the whole function,
and could be done after we copy all the code from all the inlinings, which is
what this PR does: it splits doInlining() into one function that inlines code and
one that does the updates after, and the update is done after all inlinings.

This turns out to be very important, a 5x speedup on two large real-world wasm
files I am looking at. The reason is that we actually inline more than once in
half the cases, and sometimes far more - in one case we inline over 1,000
times into a function! (and ReFinalized 1,000 times too many)

This is practically NFC, but it turns out that there are some tiny noticeable
differences between running ReFinalize once at the end vs. once after each
inlining. These differences are not really functional or observable in the
behavior of the code, and optimizations would remove them anyhow, but
they are noticeable in two tests here. The changes to tests are, in order:

* Different block names, just because the counter we use sees more things.
* In a testcase with unreachable code, we inline twice into a function, and
  the first inlining brings in an unreachable, and ReFinalizing early will lead
  to it propagating differently than if we wait to ReFinalize. (It actually leads
  to another cycle of inlining in that case, as a fluke.)

src/passes/Inlining.cpp

@@ -446,11 +446,11 @@ struct Updater : public TryDepthWalker<Updater> {
 };
 
 // Core inlining logic. Modifies the outside function (adding locals as
-// needed).
-static void doInlining(Module* module,
-                       Function* into,
-                       const InliningAction& action,
-                       PassOptions& options) {
+// needed) by copying the inlined code into it.
+static void doCodeInlining(Module* module,
+                           Function* into,
+                           const InliningAction& action,
+                           PassOptions& options) {
   Function* from = action.contents;
   auto* call = (*action.callSite)->cast<Call>();
 
@@ -622,6 +622,12 @@ static void doInlining(Module* module,
     }
     *action.callSite = builder.makeSequence(old, builder.makeUnreachable());
   }
+}
+
+// Updates the outer function after we inline into it. This is a general
+// operation that does not depend on what we inlined, it just makes sure that we
+// refinalize everything, have no duplicate break labels, etc.
+static void updateAfterInlining(Module* module, Function* into) {
   // Anything we inlined into may now have non-unique label names, fix it up.
   // Note that we must do this before refinalization, as otherwise duplicate
   // block labels can lead to errors (the IR must be valid before we
@@ -635,6 +641,14 @@ static void doInlining(Module* module,
   TypeUpdating::handleNonDefaultableLocals(into, *module);
 }
 
+static void doInlining(Module* module,
+                       Function* into,
+                       const InliningAction& action,
+                       PassOptions& options) {
+  doCodeInlining(module, into, action, options);
+  updateAfterInlining(module, into);
+}
+
 // A map of function names to the inlining actions we've decided to actually
 // perform in them.
 using ChosenActions = std::unordered_map<Name, std::vector<InliningAction>>;
@@ -657,9 +671,13 @@ struct DoInlining : public Pass {
     assert(iter != chosenActions.end());
     const auto& actions = iter->second;
     assert(!actions.empty());
+
+    // Inline all the code first, then update func once at the end (which saves
+    // e.g. running ReFinalize after each action, of which there might be many).
     for (auto action : actions) {
-      doInlining(module, func, action, getPassOptions());
+      doCodeInlining(module, func, action, getPassOptions());
     }
+    updateAfterInlining(module, func);
   }
 
 private:

test/lit/passes/inlining-optimizing_optimize-level=3.wast

@@ -8820,7 +8820,7 @@
  ;; CHECK-NEXT:                      (br $__rjti$8)
  ;; CHECK-NEXT:                     )
  ;; CHECK-NEXT:                     (block $label$break$L8
- ;; CHECK-NEXT:                      (block $__rjti$20
+ ;; CHECK-NEXT:                      (block $__rjti$23
  ;; CHECK-NEXT:                       (if
  ;; CHECK-NEXT:                        (i32.and
  ;; CHECK-NEXT:                         (local.tee $9
@@ -8845,7 +8845,7 @@
  ;; CHECK-NEXT:                          (local.get $5)
  ;; CHECK-NEXT:                         )
  ;; CHECK-NEXT:                         (loop $while-in5
- ;; CHECK-NEXT:                          (br_if $__rjti$20
+ ;; CHECK-NEXT:                          (br_if $__rjti$23
  ;; CHECK-NEXT:                           (i32.eqz
  ;; CHECK-NEXT:                            (i32.load8_u
  ;; CHECK-NEXT:                             (local.get $8)
@@ -8890,7 +8890,7 @@
  ;; CHECK-NEXT:                         )
  ;; CHECK-NEXT:                        )
  ;; CHECK-NEXT:                       )
- ;; CHECK-NEXT:                       (br_if $__rjti$20
+ ;; CHECK-NEXT:                       (br_if $__rjti$23
  ;; CHECK-NEXT:                        (local.get $9)
  ;; CHECK-NEXT:                       )
  ;; CHECK-NEXT:                       (local.set $9

test/lit/passes/inlining_optimize-level=3.wast

@@ -503,36 +503,23 @@
 ;; (That avoids possible validation problems, and maximizes DCE.) To keep it
 ;; unreachable we'll add an unreachable instruction after the inlined code.
 (module
- ;; CHECK:      (type $0 (func (param f32)))
-
- ;; CHECK:      (type $1 (func))
-
- ;; CHECK:      (func $A (param $0 f32)
- ;; CHECK-NEXT:  (local $1 f32)
- ;; CHECK-NEXT:  (drop
- ;; CHECK-NEXT:   (block (result f32)
- ;; CHECK-NEXT:    (block $__inlined_func$C (result f32)
- ;; CHECK-NEXT:     (local.set $1
- ;; CHECK-NEXT:      (local.get $0)
- ;; CHECK-NEXT:     )
- ;; CHECK-NEXT:     (local.get $1)
- ;; CHECK-NEXT:    )
- ;; CHECK-NEXT:   )
- ;; CHECK-NEXT:  )
- ;; CHECK-NEXT: )
  (func $A (param $0 f32)
   (drop
    (call $C
     (local.get $0)
    )
   )
  )
+ ;; CHECK:      (type $0 (func))
+
  ;; CHECK:      (func $B
  ;; CHECK-NEXT:  (local $0 f32)
- ;; CHECK-NEXT:  (call $A
- ;; CHECK-NEXT:   (block
- ;; CHECK-NEXT:    (block
- ;; CHECK-NEXT:     (drop
+ ;; CHECK-NEXT:  (local $1 f32)
+ ;; CHECK-NEXT:  (local $2 f32)
+ ;; CHECK-NEXT:  (block
+ ;; CHECK-NEXT:   (block $__inlined_func$A$3
+ ;; CHECK-NEXT:    (local.set $1
+ ;; CHECK-NEXT:     (block (result f32)
  ;; CHECK-NEXT:      (block $__inlined_func$C$2 (result f32)
  ;; CHECK-NEXT:       (local.tee $0
  ;; CHECK-NEXT:        (block
@@ -544,7 +531,19 @@
  ;; CHECK-NEXT:       (local.get $0)
  ;; CHECK-NEXT:      )
  ;; CHECK-NEXT:     )
- ;; CHECK-NEXT:     (unreachable)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:    (local.set $2
+ ;; CHECK-NEXT:     (f32.const 0)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:    (drop
+ ;; CHECK-NEXT:     (block (result f32)
+ ;; CHECK-NEXT:      (block $__inlined_func$C (result f32)
+ ;; CHECK-NEXT:       (local.set $2
+ ;; CHECK-NEXT:        (local.get $1)
+ ;; CHECK-NEXT:       )
+ ;; CHECK-NEXT:       (local.get $2)
+ ;; CHECK-NEXT:      )
+ ;; CHECK-NEXT:     )
  ;; CHECK-NEXT:    )
  ;; CHECK-NEXT:   )
  ;; CHECK-NEXT:  )