[NFC] Move optimizeSubsequentStructSet() to a new pass, HeapStoreOptimization (#6882)

This just moves code out of OptimizeInstructions to the new pass. The existing
test is renamed and now runs the new pass instead. The new pass is run right
after each --optimize-instructions invocation, so it should not cause any
noticeable effects whatsoever, making this NFC.

The motivation here is that there is a bug in the pass, see the new testcase
added at the end, which shows the bug. It is not practical to fix that bug in
OptimizeInstructions since we need more than peephole optimizations to do
so. This PR moves the code to a new pass so we can fix it there properly,
later.

The new pass is named HeapStoreOptimization since the same infrastructure
we will need to fix the bug will also help dead store elimination and related
things.

5 files changed, 62 insertions, 2 deletions

diff --git a/test/lit/help/wasm-metadce.test b/test/lit/help/wasm-metadce.test
index 665d78746..41a43bf1b 100644
--- a/test/lit/help/wasm-metadce.test
+++ b/test/lit/help/wasm-metadce.test
@@ -190,6 +190,8 @@
 ;; CHECK-NEXT:   --gufa-optimizing                             GUFA plus local optimizations in
 ;; CHECK-NEXT:                                                 functions we modified
 ;; CHECK-NEXT:
+;; CHECK-NEXT:   --heap-store-optimization                     optimize heap (GC) stores
+;; CHECK-NEXT:
 ;; CHECK-NEXT:   --heap2local                                  replace GC allocations with
 ;; CHECK-NEXT:                                                 locals
 ;; CHECK-NEXT:
diff --git a/test/lit/help/wasm-opt.test b/test/lit/help/wasm-opt.test
index 4eea3c431..e5b30e304 100644
--- a/test/lit/help/wasm-opt.test
+++ b/test/lit/help/wasm-opt.test
@@ -199,6 +199,8 @@
 ;; CHECK-NEXT:   --gufa-optimizing                             GUFA plus local optimizations in
 ;; CHECK-NEXT:                                                 functions we modified
 ;; CHECK-NEXT:
+;; CHECK-NEXT:   --heap-store-optimization                     optimize heap (GC) stores
+;; CHECK-NEXT:
 ;; CHECK-NEXT:   --heap2local                                  replace GC allocations with
 ;; CHECK-NEXT:                                                 locals
 ;; CHECK-NEXT:
diff --git a/test/lit/help/wasm2js.test b/test/lit/help/wasm2js.test
index 501d1d3f1..2d933984e 100644
--- a/test/lit/help/wasm2js.test
+++ b/test/lit/help/wasm2js.test
@@ -153,6 +153,8 @@
 ;; CHECK-NEXT:   --gufa-optimizing                             GUFA plus local optimizations in
 ;; CHECK-NEXT:                                                 functions we modified
 ;; CHECK-NEXT:
+;; CHECK-NEXT:   --heap-store-optimization                     optimize heap (GC) stores
+;; CHECK-NEXT:
 ;; CHECK-NEXT:   --heap2local                                  replace GC allocations with
 ;; CHECK-NEXT:                                                 locals
 ;; CHECK-NEXT:
diff --git a/test/lit/passes/O1.wast b/test/lit/passes/O1.wast
index 8ffc29301..49271699d 100644
--- a/test/lit/passes/O1.wast
+++ b/test/lit/passes/O1.wast
@@ -40,4 +40,3 @@
  )
 )
 
-
diff --git a/test/lit/passes/optimize-instructions-gc-heap.wast b/test/lit/passes/heap-store-optimization.wast
index 2988b1bd8..635963523 100644
--- a/test/lit/passes/optimize-instructions-gc-heap.wast
+++ b/test/lit/passes/heap-store-optimization.wast
@@ -1,5 +1,5 @@
 ;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
-;; RUN: wasm-opt %s --remove-unused-names --optimize-instructions -all -S -o - \
+;; RUN: wasm-opt %s --remove-unused-names --heap-store-optimization -all -S -o - \
 ;; RUN:   | filecheck %s
 ;;
 ;; --remove-unused-names allows the optimizer to see that the blocks have no
@@ -822,4 +822,59 @@
   (func $helper-i32 (param $x i32) (result i32)
     (i32.const 42)
   )
+
+  ;; CHECK:      (func $control-flow-in-set-value (type $5) (result i32)
+  ;; CHECK-NEXT:  (local $ref (ref null $struct))
+  ;; CHECK-NEXT:  (block $label
+  ;; CHECK-NEXT:   (local.set $ref
+  ;; CHECK-NEXT:    (struct.new $struct
+  ;; CHECK-NEXT:     (if (result i32)
+  ;; CHECK-NEXT:      (i32.const 1)
+  ;; CHECK-NEXT:      (then
+  ;; CHECK-NEXT:       (br $label)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:      (else
+  ;; CHECK-NEXT:       (i32.const 42)
+  ;; CHECK-NEXT:      )
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (struct.get $struct 0
+  ;; CHECK-NEXT:   (local.get $ref)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $control-flow-in-set-value (result i32)
+    ;; Test we handle control flow in the struct.set's value when we combine a
+    ;; struct.set with a struct.new.
+    ;; XXX The output above is wrong atm, and the pass needs fixing!
+    (local $ref (ref null $struct))
+    (block $label
+      (struct.set $struct 0
+        (local.tee $ref
+          (struct.new $struct
+            (i32.const 1)
+          )
+        )
+        (if (result i32)
+          (i32.const 1)
+          (then
+            ;; This conditional break happens *after* the local.tee of $ref. We
+            ;; must not move code around that reorders it, since there is a use
+            ;; of the local below that could notice changes.
+            (br $label)
+          )
+          (else
+            (i32.const 42)
+          )
+        )
+      )
+    )
+    ;; We did not reach the struct.set, but we did reach the local.tee, so this
+    ;; reads the initial value of 1 (and does not trap on a nullref).
+    (struct.get $struct 0
+      (local.get $ref)
+    )
+  )
 )
+