[#CLJ-740] Unnecessary boxing of primitives in case form - Clojure JIRA

Details

Type: Defect
Status: Open
Priority: Major
Resolution: Unresolved
Affects Version/s: Release 1.3
Fix Version/s: None
Component/s: None
Labels:
None

Description

Found this while profiling some performance-critical code.

Consider the following Clojure function:

(defn test-case ^double [^long i ^double d1 ^double d2]
  (case (int i)
    0 d1
    d2))

Current Clojure 1.3 snapshot compiles it to:

public final double invokePrim(long, double, double)   throws java.lang.Exception;
  Code:
   0:	lload_1
   1:	invokestatic	#67; //Method clojure/lang/RT.intCast:(J)I
   4:	istore	7
   6:	iload	7
   8:	i2l
   9:	invokestatic	#73; //Method clojure/lang/Numbers.num:(J)Ljava/lang/Number;
   12:	invokestatic	#79; //Method clojure/lang/Util.hash:(Ljava/lang/Object;)I
   15:	iconst_0
   16:	ishr
   17:	iconst_1
   18:	iand
   19:	tableswitch{ //0 to 0
		0: 36;
		default: 58 }
   36:	iload	7
   38:	i2l
   39:	invokestatic	#73; //Method clojure/lang/Numbers.num:(J)Ljava/lang/Number;
   42:	getstatic	#45; //Field const__3:Ljava/lang/Object;
   45:	invokestatic	#83; //Method clojure/lang/Util.equals:(Ljava/lang/Object;Ljava/lang/Object;)Z
   48:	ifeq	58
   51:	dload_3
   52:	invokestatic	#88; //Method java/lang/Double.valueOf:(D)Ljava/lang/Double;
   55:	goto	63
   58:	dload	5
   60:	invokestatic	#88; //Method java/lang/Double.valueOf:(D)Ljava/lang/Double;
   63:	checkcast	#92; //class java/lang/Number
   66:	invokevirtual	#96; //Method java/lang/Number.doubleValue:()D
   69:	dreturn
}

This bytecode contains boxing of primitives (calls to clojure/lang/Numbers.num and java/lang/Double.valueOf) and calls to clojure/lang/Util.hash and clojure/lang/Util.equals that does not seem necessary.

At 60-66 primitive double is boxed into Double only to be converted back into primitive.

The equivalent Java code compiles to much simpler and faster bytecode:

public double testCase(long, double, double);
  Code:
   0:	lload_1
   1:	l2i
   2:	lookupswitch{ //1
		0: 20;
		default: 22 }
   20:	dload_3
   21:	dreturn
   22:	dload	5
   24:	dreturn
}

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Alexander Taggart added a comment - 28/Feb/11 2:16 PM - edited

Improved via patch on ~~CLJ-426~~.

(defn test-case ^double [^long i ^double d1 ^double d2]
  (case (int i)
    0 d1
    d2))

now emits as

 0  lload_1 [i]
 1  invokestatic clojure.lang.RT.intCast(long) : int [67]
 4  istore 7 [G__7903] // let-bound expression
 6  iload 7 [G__7903]
 8  tableswitch default: 32
      case 0: 28
28  dload_3 [d2]
29  goto 34
32  dload 5 [arg2]
34  dreturn

or if the int cast of the expression is omitted:

 0  lload_1 [i]
 1  lstore 7 [G__7903] // let-bound expression
 3  lload 7 [G__7903]
 5  l2i
 6  tableswitch default: 35
      case 0: 24
24  lconst_0           // match, verify long expr wasn't truncated
25  lload 7 [G__7903]
27  lcmp
28  ifne 35
31  dload_3 [d2]
32  goto 37
35  dload 5 [arg2]
37  dreturn

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Alexander Taggart added a comment - 28/Feb/11 2:16 PM - edited Improved via patch on ~~CLJ-426~~.

(defn test-case ^double [^long i ^double d1 ^double d2]
  (case (int i)
    0 d1
    d2))

now emits as

 0  lload_1 [i]
 1  invokestatic clojure.lang.RT.intCast(long) : int [67]
 4  istore 7 [G__7903] // let-bound expression
 6  iload 7 [G__7903]
 8  tableswitch default: 32
      case 0: 28
28  dload_3 [d2]
29  goto 34
32  dload 5 [arg2]
34  dreturn

or if the int cast of the expression is omitted:

 0  lload_1 [i]
 1  lstore 7 [G__7903] // let-bound expression
 3  lload 7 [G__7903]
 5  l2i
 6  tableswitch default: 35
      case 0: 24
24  lconst_0           // match, verify long expr wasn't truncated
25  lload 7 [G__7903]
27  lcmp
28  ifne 35
31  dload_3 [d2]
32  goto 37
35  dload 5 [arg2]
37  dreturn

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Unnecessary boxing of primitives in case form

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