RemoveUnusedBrs::tablify() improvements: handle EqZ and tee (#4144)

tablify() attempts to turns a sequence of br_ifs into a single
br_table. This PR adds some flexibility to the specific pattern it
looks for, specifically:

  *  Accept i32.eqz as a comparison to zero, and not just to look
     for i32.eq against a constant.
  *  Allow the first condition to be a tee. If it is, compare later
     conditions to local.get of that local.

This will allow more br_tables to be emitted in j2cl output.

2 files changed, 190 insertions, 0 deletions

diff --git a/test/passes/remove-unused-brs_enable-multivalue.txt b/test/passes/remove-unused-brs_enable-multivalue.txt
index 29b5eca5e..46938f784 100644
--- a/test/passes/remove-unused-brs_enable-multivalue.txt
+++ b/test/passes/remove-unused-brs_enable-multivalue.txt
@@ -1669,6 +1669,109 @@
   )
   (unreachable)
  )
+ (func $br-to-table-initial-tee (param $a i32)
+  (block $x
+   (block $y
+    (block $z
+     (nop)
+     (nop)
+     (block $tablify|0
+      (br_table $x $y $z $tablify|0
+       (i32.sub
+        (local.tee $a
+         (i32.add
+          (i32.const 10)
+          (i32.const 1)
+         )
+        )
+        (i32.const 10)
+       )
+      )
+     )
+     (unreachable)
+    )
+    (unreachable)
+   )
+   (unreachable)
+  )
+  (unreachable)
+ )
+ (func $br-to-table-initial-tee-wrong-index (param $a i32)
+  (local $b i32)
+  (block $x
+   (block $y
+    (block $z
+     (br_if $x
+      (i32.eq
+       (local.tee $a
+        (i32.const 99)
+       )
+       (i32.const 10)
+      )
+     )
+     (br_if $y
+      (i32.eq
+       (local.get $b)
+       (i32.const 11)
+      )
+     )
+     (br_if $z
+      (i32.eq
+       (local.get $b)
+       (i32.const 12)
+      )
+     )
+     (unreachable)
+    )
+    (unreachable)
+   )
+   (unreachable)
+  )
+  (unreachable)
+ )
+ (func $br-to-table-eqz (param $a i32)
+  (block $x
+   (block $y
+    (block $z
+     (nop)
+     (nop)
+     (block $tablify|0
+      (br_table $x $y $z $tablify|0
+       (local.get $a)
+      )
+     )
+     (unreachable)
+    )
+    (unreachable)
+   )
+   (unreachable)
+  )
+  (unreachable)
+ )
+ (func $br-to-table-tee-eqz (param $a i32)
+  (block $x
+   (block $y
+    (block $z
+     (nop)
+     (nop)
+     (block $tablify|0
+      (br_table $x $y $z $tablify|0
+       (local.tee $a
+        (i32.add
+         (i32.const 0)
+         (i32.const 1)
+        )
+       )
+      )
+     )
+     (unreachable)
+    )
+    (unreachable)
+   )
+   (unreachable)
+  )
+  (unreachable)
+ )
  (func $tiny-switch
   (if
    (i32.const 0)
diff --git a/test/passes/remove-unused-brs_enable-multivalue.wast b/test/passes/remove-unused-brs_enable-multivalue.wast
index afc8c3836..ae8878e00 100644
--- a/test/passes/remove-unused-brs_enable-multivalue.wast
+++ b/test/passes/remove-unused-brs_enable-multivalue.wast
@@ -1353,6 +1353,93 @@
     )
     (unreachable)
   )
+  (func $br-to-table-initial-tee (param $a i32)
+    (block $x
+      (block $y
+        (block $z
+          (br_if $x
+            (i32.eq
+              (local.tee $a
+                (i32.add
+                  (i32.const 10)
+                  (i32.const 1)
+                )
+              )
+              (i32.const 10)
+            )
+          )
+          (br_if $y (i32.eq (local.get $a) (i32.const 11)))
+          (br_if $z (i32.eq (local.get $a) (i32.const 12)))
+          (unreachable)
+        )
+        (unreachable)
+      )
+      (unreachable)
+    )
+    (unreachable)
+  )
+  (func $br-to-table-initial-tee-wrong-index (param $a i32)
+    (local $b i32)
+    (block $x
+      (block $y
+        (block $z
+          (br_if $x
+            (i32.eq
+              (local.tee $a (i32.const 99))
+              (i32.const 10)
+            )
+          )
+          ;; The subsequent conditions use a different local, $b, so we cannot
+          ;; optimize here.
+          (br_if $y (i32.eq (local.get $b) (i32.const 11)))
+          (br_if $z (i32.eq (local.get $b) (i32.const 12)))
+          (unreachable)
+        )
+        (unreachable)
+      )
+      (unreachable)
+    )
+    (unreachable)
+  )
+  (func $br-to-table-eqz (param $a i32)
+    (block $x
+      (block $y
+        (block $z
+          (br_if $x (i32.eqz (local.get $a)))
+          (br_if $y (i32.eq (local.get $a) (i32.const 1)))
+          (br_if $z (i32.eq (local.get $a) (i32.const 2)))
+          (unreachable)
+        )
+        (unreachable)
+      )
+      (unreachable)
+    )
+    (unreachable)
+  )
+  (func $br-to-table-tee-eqz (param $a i32)
+    (block $x
+      (block $y
+        (block $z
+          (br_if $x
+            (i32.eqz
+              (local.tee $a
+                (i32.add
+                  (i32.const 0)
+                  (i32.const 1)
+                )
+              )
+            )
+          )
+          (br_if $y (i32.eq (local.get $a) (i32.const 1)))
+          (br_if $z (i32.eq (local.get $a) (i32.const 2)))
+          (unreachable)
+        )
+        (unreachable)
+      )
+      (unreachable)
+    )
+    (unreachable)
+  )
   (func $tiny-switch
     (block $x
       (block $y