Improve const folding via early precompute (#1439)

Author: MaxGraey

src/module.ts

@@ -1514,6 +1514,7 @@ export class Module {
         passes.push("remove-unused-brs");
         passes.push("remove-unused-names");
         passes.push("merge-blocks");
+        passes.push("precompute");
       }
       if (optimizeLevel >= 3) {
         passes.push("flatten");
@@ -1545,7 +1546,6 @@ export class Module {
       } else {
         passes.push("precompute");
       }
-      passes.push("vacuum");
       if (optimizeLevel >= 2 || shrinkLevel >= 1) {
         passes.push("pick-load-signs");
         passes.push("simplify-globals-optimizing");
@@ -1633,7 +1633,6 @@ export class Module {
           passes.push("vacuum");
 
           passes.push("precompute-propagate");
-          passes.push("vacuum");
 
           // replace indirect with direct calls again and inline
           passes.push("inlining-optimizing");

tests/compiler/const-folding.json

@@ -0,0 +1,5 @@
+{
+  "asc_flags": [
+    "--runtime none"
+  ]
+}

tests/compiler/const-folding.optimized.wat

@@ -0,0 +1,15 @@
+(module
+ (type $i64_=>_i64 (func (param i64) (result i64)))
+ (memory $0 0)
+ (export "memory" (memory $0))
+ (export "test" (func $const-folding/test))
+ (func $const-folding/test (param $0 i64) (result i64)
+  local.get $0
+  i64.const 1
+  i64.shl
+  local.get $0
+  i64.const 63
+  i64.shr_u
+  i64.add
+ )
+)

tests/compiler/const-folding.ts

@@ -0,0 +1,11 @@
+export function test(value: u64): u64 {
+  var mod1: u64 = -1;
+  var mod2: u64 = -1;
+
+  var rlo = value << 1;
+  var rhi = rlo & ~mod2;
+
+  rhi |= rhi << 1;
+  rhi |= (value >> 63) & mod1;
+  return rlo + rhi;
+}

tests/compiler/const-folding.untouched.wat

@@ -0,0 +1,44 @@
+(module
+ (type $i64_=>_i64 (func (param i64) (result i64)))
+ (memory $0 0)
+ (table $0 1 funcref)
+ (export "memory" (memory $0))
+ (export "test" (func $const-folding/test))
+ (func $const-folding/test (param $0 i64) (result i64)
+  (local $1 i64)
+  (local $2 i64)
+  (local $3 i64)
+  (local $4 i64)
+  i64.const -1
+  local.set $1
+  i64.const -1
+  local.set $2
+  local.get $0
+  i64.const 1
+  i64.shl
+  local.set $3
+  local.get $3
+  local.get $2
+  i64.const -1
+  i64.xor
+  i64.and
+  local.set $4
+  local.get $4
+  local.get $4
+  i64.const 1
+  i64.shl
+  i64.or
+  local.set $4
+  local.get $4
+  local.get $0
+  i64.const 63
+  i64.shr_u
+  local.get $1
+  i64.and
+  i64.or
+  local.set $4
+  local.get $3
+  local.get $4
+  i64.add
+ )
+)