[Wasm GC] SimplifyLocals: Switch local.get to use a more refined type when possible (#5194)

(local.set $refined (cast (local.get $plain)))
..
.. (local.get $plain) .. ;; we can change this to read from $refined

By using the more refined type we may be able to eliminate casts later.

To do this, look at the fallthrough value (so we can look through a cast or a block
value - this is the reason for the small wasm2js improvements in tests), and also
extend the code that picks which local index to read to look at types (previously
we just ignored any pairs of locals with different types).

6 files changed, 194 insertions, 53 deletions

diff --git a/test/lit/passes/simplify-locals-gc.wast b/test/lit/passes/simplify-locals-gc.wast
index 75be02cf2..951116a08 100644
--- a/test/lit/passes/simplify-locals-gc.wast
+++ b/test/lit/passes/simplify-locals-gc.wast
@@ -445,4 +445,168 @@
     ;; Helper function for the above.
     (unreachable)
   )
+
+  ;; CHECK:      (func $pick-refined (param $nn-any (ref any)) (result anyref)
+  ;; CHECK-NEXT:  (local $any anyref)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT:  (call $use-any
+  ;; CHECK-NEXT:   (local.get $nn-any)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (call $use-nn-any
+  ;; CHECK-NEXT:   (local.get $nn-any)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT:  (local.get $nn-any)
+  ;; CHECK-NEXT: )
+  ;; NOMNL:      (func $pick-refined (type $ref|any|_=>_anyref) (param $nn-any (ref any)) (result anyref)
+  ;; NOMNL-NEXT:  (local $any anyref)
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT:  (call $use-any
+  ;; NOMNL-NEXT:   (local.get $nn-any)
+  ;; NOMNL-NEXT:  )
+  ;; NOMNL-NEXT:  (call $use-nn-any
+  ;; NOMNL-NEXT:   (local.get $nn-any)
+  ;; NOMNL-NEXT:  )
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT:  (local.get $nn-any)
+  ;; NOMNL-NEXT: )
+  (func $pick-refined (param $nn-any (ref any)) (result anyref)
+    (local $any anyref)
+    (local.set $any
+      (local.get $nn-any)
+    )
+    ;; Use the locals so neither is trivially removed.
+    (call $use-any
+      (local.get $any)
+    )
+    (call $use-nn-any
+      (local.get $nn-any)
+    )
+    ;; This copy is not needed, as they hold the same value.
+    (local.set $any
+      (local.get $nn-any)
+    )
+    ;; This local.get might as well use the non-nullable local, which is more
+    ;; refined. In fact, all uses of locals can be switched to that one in the
+    ;; entire function (and the other local would be removed by other passes).
+    (local.get $any)
+  )
+
+  ;; CHECK:      (func $pick-casted (param $any anyref) (result anyref)
+  ;; CHECK-NEXT:  (local $nn-any (ref any))
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT:  (call $use-any
+  ;; CHECK-NEXT:   (local.tee $nn-any
+  ;; CHECK-NEXT:    (ref.as_non_null
+  ;; CHECK-NEXT:     (local.get $any)
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (call $use-nn-any
+  ;; CHECK-NEXT:   (local.get $nn-any)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT:  (local.get $nn-any)
+  ;; CHECK-NEXT: )
+  ;; NOMNL:      (func $pick-casted (type $anyref_=>_anyref) (param $any anyref) (result anyref)
+  ;; NOMNL-NEXT:  (local $nn-any (ref any))
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT:  (call $use-any
+  ;; NOMNL-NEXT:   (local.tee $nn-any
+  ;; NOMNL-NEXT:    (ref.as_non_null
+  ;; NOMNL-NEXT:     (local.get $any)
+  ;; NOMNL-NEXT:    )
+  ;; NOMNL-NEXT:   )
+  ;; NOMNL-NEXT:  )
+  ;; NOMNL-NEXT:  (call $use-nn-any
+  ;; NOMNL-NEXT:   (local.get $nn-any)
+  ;; NOMNL-NEXT:  )
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT:  (local.get $nn-any)
+  ;; NOMNL-NEXT: )
+  (func $pick-casted (param $any anyref) (result anyref)
+    (local $nn-any (ref any))
+    (local.set $nn-any
+      (ref.as_non_null
+        (local.get $any)
+      )
+    )
+    ;; Use the locals so neither is trivially removed.
+    (call $use-any
+      (local.get $any)
+    )
+    (call $use-nn-any
+      (local.get $nn-any)
+    )
+    ;; This copy is not needed, as they hold the same value.
+    (local.set $any
+      (local.get $nn-any)
+    )
+    ;; This local.get might as well use the non-nullable local.
+    (local.get $any)
+  )
+
+  ;; CHECK:      (func $pick-fallthrough (param $x i32)
+  ;; CHECK-NEXT:  (local $t i32)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (local.get $x)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (block (result i32)
+  ;; CHECK-NEXT:    (local.get $x)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  ;; NOMNL:      (func $pick-fallthrough (type $i32_=>_none) (param $x i32)
+  ;; NOMNL-NEXT:  (local $t i32)
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT:  (drop
+  ;; NOMNL-NEXT:   (local.get $x)
+  ;; NOMNL-NEXT:  )
+  ;; NOMNL-NEXT:  (drop
+  ;; NOMNL-NEXT:   (block (result i32)
+  ;; NOMNL-NEXT:    (local.get $x)
+  ;; NOMNL-NEXT:   )
+  ;; NOMNL-NEXT:  )
+  ;; NOMNL-NEXT: )
+  (func $pick-fallthrough (param $x i32)
+    (local $t i32)
+    ;; Similar to the above test wth looking through a cast, but using a non-gc
+    ;; type of fallthrough value.
+    (local.set $t
+      (block (result i32)
+        (local.get $x)
+      )
+    )
+    ;; The locals are identical, as we set $t = $x (we can look through to the
+    ;; block value). Both these gets can go to $x, and we do not need to set $t
+    ;; as it will have 0 uses.
+    (drop
+      (local.get $x)
+    )
+    (drop
+      (local.get $t)
+    )
+  )
+
+  ;; CHECK:      (func $use-nn-any (param $nn-any (ref any))
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  ;; NOMNL:      (func $use-nn-any (type $ref|any|_=>_none) (param $nn-any (ref any))
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT: )
+  (func $use-nn-any (param $nn-any (ref any))
+    ;; Helper function for the above.
+  )
+
+  ;; CHECK:      (func $use-any (param $any anyref)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  ;; NOMNL:      (func $use-any (type $anyref_=>_none) (param $any anyref)
+  ;; NOMNL-NEXT:  (nop)
+  ;; NOMNL-NEXT: )
+  (func $use-any (param $any anyref)
+    ;; Helper function for the above.
+  )
 )
diff --git a/test/wasm2js/conversions-modified.2asm.js.opt b/test/wasm2js/conversions-modified.2asm.js.opt
index 36bfda8cb..4c2b6d1ae 100644
--- a/test/wasm2js/conversions-modified.2asm.js.opt
+++ b/test/wasm2js/conversions-modified.2asm.js.opt
@@ -162,9 +162,8 @@ function asmFunc(imports) {
   $1 = wasm2js_scratch_load_i32(1) | 0;
   $2 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $1;
-  $1 = $2;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $1;
+  return $2;
  }
  
  return {
diff --git a/test/wasm2js/float_literals-modified.2asm.js.opt b/test/wasm2js/float_literals-modified.2asm.js.opt
index 1e69b6304..613e52a40 100644
--- a/test/wasm2js/float_literals-modified.2asm.js.opt
+++ b/test/wasm2js/float_literals-modified.2asm.js.opt
@@ -108,9 +108,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$32() {
@@ -119,9 +118,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$34() {
@@ -130,9 +128,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$35() {
@@ -141,9 +138,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$36() {
@@ -152,9 +148,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$37() {
@@ -163,9 +158,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$38() {
@@ -174,9 +168,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$39() {
@@ -185,9 +178,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$41() {
@@ -196,9 +188,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$42() {
@@ -207,9 +198,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$44() {
@@ -218,9 +208,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$45() {
@@ -229,9 +218,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$46() {
@@ -240,9 +228,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$47() {
@@ -251,9 +238,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$48() {
@@ -262,9 +248,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$49() {
@@ -273,9 +258,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$50() {
@@ -284,9 +268,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  function legalstub$59() {
@@ -295,9 +278,8 @@ function asmFunc(imports) {
   $0_1 = wasm2js_scratch_load_i32(1) | 0;
   $1 = wasm2js_scratch_load_i32(0) | 0;
   i64toi32_i32$HIGH_BITS = $0_1;
-  $0_1 = $1;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0_1;
+  return $1;
  }
  
  return {
diff --git a/test/wasm2js/i64-ctz.2asm.js.opt b/test/wasm2js/i64-ctz.2asm.js.opt
index c232bef7c..0d6ffd697 100644
--- a/test/wasm2js/i64-ctz.2asm.js.opt
+++ b/test/wasm2js/i64-ctz.2asm.js.opt
@@ -22,7 +22,7 @@ function asmFunc(imports) {
   while (1) {
    if ($0 | $2) {
     $1 = $0;
-    $0 = $0 - 1 & $0;
+    $0 = $1 & $1 - 1;
     $2 = $2 - !$1 & $2;
     $3 = $3 + 1 | 0;
     $4 = $3 ? $4 : $4 + 1 | 0;
@@ -31,9 +31,8 @@ function asmFunc(imports) {
    break;
   };
   i64toi32_i32$HIGH_BITS = $4;
-  $0 = $3;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0;
+  return $3;
  }
  
  function legalstub$ctz64($0, $1) {
diff --git a/test/wasm2js/stack-modified.2asm.js.opt b/test/wasm2js/stack-modified.2asm.js.opt
index c3d9d7d57..45203a50e 100644
--- a/test/wasm2js/stack-modified.2asm.js.opt
+++ b/test/wasm2js/stack-modified.2asm.js.opt
@@ -17,24 +17,21 @@ function asmFunc(imports) {
  var setTempRet0 = env.setTempRet0;
  var i64toi32_i32$HIGH_BITS = 0;
  function legalstub$0($0, $1) {
-  var $2 = 0, $3 = 0, $4 = 0;
-  $2 = $1;
-  $3 = 1;
+  var $2 = 0, $3 = 0;
+  $2 = 1;
   while (1) {
-   if ($0 | $2) {
-    $3 = __wasm_i64_mul($0, $2, $3, $4);
-    $4 = i64toi32_i32$HIGH_BITS;
-    $1 = $0;
+   if ($0 | $1) {
+    $2 = __wasm_i64_mul($0, $1, $2, $3);
+    $3 = i64toi32_i32$HIGH_BITS;
+    $1 = $1 - !$0 | 0;
     $0 = $0 - 1 | 0;
-    $2 = $2 - !$1 | 0;
     continue;
    }
    break;
   };
-  i64toi32_i32$HIGH_BITS = $4;
-  $0 = $3;
+  i64toi32_i32$HIGH_BITS = $3;
   setTempRet0(i64toi32_i32$HIGH_BITS | 0);
-  return $0;
+  return $2;
  }
  
  function __wasm_i64_mul($0, $1, $2, $3) {
diff --git a/test/wasm2js/unary-ops.2asm.js.opt b/test/wasm2js/unary-ops.2asm.js.opt
index 4da12af66..bca65089b 100644
--- a/test/wasm2js/unary-ops.2asm.js.opt
+++ b/test/wasm2js/unary-ops.2asm.js.opt
@@ -48,7 +48,7 @@ function asmFunc(imports) {
   while (1) {
    if ($1_1 | $4) {
     $0 = $4;
-    $4 = $4 - 1 & $4;
+    $4 = $0 & $0 - 1;
     $1_1 = $1_1 - !$0 & $1_1;
     $5 = $5 + 1 | 0;
     $6_1 = $5 ? $6_1 : $6_1 + 1 | 0;