Optimize repeat loop

Author: MaxGraey

std/assembly/string.ts

@@ -396,15 +396,18 @@ export class String {
  if (count === 0 || !this.length) return EMPTY;
  if (count === 1) return this;
 
- var str  = changetype<String>(this);
- var result = EMPTY;
+ var result = changetype<String>(this);
+ var isOdd = count & 1;
 
- while (count) {
- if (count & 1) result = result.concat(str);
- if (count > 1) str = str.concat(str);
+ while (count > 1) {
+ result = result.concat(result);
  count >>= 1;
  }
 
+ if (isOdd) {
+ return result.concat(this);
+ }
+
  return result;
  }
 

tests/compiler/std/string.optimized.wat

@@ -1088,7 +1088,7 @@
  (call $abort
  (i32.const 0)
  (i32.const 72)
- (i32.const 590)
+ (i32.const 593)
  (i32.const 10)
  )
  (unreachable)
@@ -3664,6 +3664,7 @@
  )
  (func $~lib/string/String#repeat (; 28 ;) (type $iii) (param $0 i32) (param $1 i32) (result i32)
  (local $2 i32)
+ (local $3 i32)
  (if
  (i32.eqz
  (get_local $0)
@@ -3744,34 +3745,25 @@
  )
  )
  (set_local $2
- (i32.const 332)
+ (get_local $0)
+ )
+ (set_local $3
+ (i32.and
+ (get_local $1)
+ (i32.const 1)
+ )
  )
  (loop $continue|0
  (if
- (get_local $1)
+ (i32.gt_s
+ (get_local $1)
+ (i32.const 1)
+ )
  (block
- (if
- (i32.and
- (get_local $1)
- (i32.const 1)
- )
- (set_local $2
- (call $~lib/string/String#concat
- (get_local $2)
- (get_local $0)
- )
- )
- )
- (if
- (i32.gt_s
- (get_local $1)
- (i32.const 1)
- )
- (set_local $0
- (call $~lib/string/String#concat
- (get_local $0)
- (get_local $0)
- )
+ (set_local $2
+ (call $~lib/string/String#concat
+ (get_local $2)
+ (get_local $2)
  )
  )
  (set_local $1
@@ -3784,6 +3776,15 @@
  )
  )
  )
+ (if
+ (get_local $3)
+ (return
+ (call $~lib/string/String#concat
+ (get_local $2)
+ (get_local $0)
+ )
+ )
+ )
  (get_local $2)
  )
  (func $~lib/string/String#repeat|trampoline (; 29 ;) (type $iii) (param $0 i32) (param $1 i32) (result i32)

tests/compiler/std/string.untouched.wat

@@ -1266,7 +1266,7 @@
  (call $abort
  (i32.const 0)
  (i32.const 72)
- (i32.const 590)
+ (i32.const 593)
  (i32.const 10)
  )
  (unreachable)
@@ -4320,36 +4320,24 @@
  (get_local $0)
  )
  (set_local $4
- (i32.const 332)
+ (i32.and
+ (get_local $1)
+ (i32.const 1)
+ )
  )
  (block $break|0
  (loop $continue|0
  (if
- (get_local $1)
+ (i32.gt_s
+ (get_local $1)
+ (i32.const 1)
+ )
  (block
  (block
- (if
- (i32.and
- (get_local $1)
- (i32.const 1)
- )
- (set_local $4
- (call $~lib/string/String#concat
- (get_local $4)
- (get_local $3)
- )
- )
- )
- (if
- (i32.gt_s
- (get_local $1)
- (i32.const 1)
- )
- (set_local $3
- (call $~lib/string/String#concat
- (get_local $3)
- (get_local $3)
- )
+ (set_local $3
+ (call $~lib/string/String#concat
+ (get_local $3)
+ (get_local $3)
  )
  )
  (set_local $1
@@ -4364,8 +4352,17 @@
  )
  )
  )
- (return
+ (if
  (get_local $4)
+ (return
+ (call $~lib/string/String#concat
+ (get_local $3)
+ (get_local $0)
+ )
+ )
+ )
+ (return
+ (get_local $3)
  )
  )
  (func $~lib/string/String#repeat|trampoline (; 29 ;) (type $iii) (param $0 i32) (param $1 i32) (result i32)