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comparison graal/com.oracle.truffle.api/src/com/oracle/truffle/api/CompilerDirectives.java @ 9319:1188b7c42196

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Changed the behavior of CompilerDirectives.injectBranchProbability and added javadoc to document the new behavior. Introduced probability constants. Removed CompilerDirectives.slowpath().
author Thomas Wuerthinger <thomas.wuerthinger@oracle.com>
date Thu, 25 Apr 2013 22:44:28 +0200
parents 6369d37b37d1
children 0fccad3ce40d
comparison
equal deleted inserted replaced
9318:dc04c7e8f714 9319:1188b7c42196
29 * Directives that influence the optimizations of the Truffle compiler. All of the operations have 29 * Directives that influence the optimizations of the Truffle compiler. All of the operations have
30 * no effect when executed in the Truffle interpreter. 30 * no effect when executed in the Truffle interpreter.
31 */ 31 */
32 public class CompilerDirectives { 32 public class CompilerDirectives {
33 33
34 private static final double SLOWPATH_PROBABILITY = 0.0001; 34 public static final double LIKELY_PROBABILITY = 0.75;
35 public static final double UNLIKELY_PROBABILITY = 1.0 - LIKELY_PROBABILITY;
36
37 public static final double SLOWPATH_PROBABILITY = 0.0001;
38 public static final double FASTPATH_PROBABILITY = 1.0 - SLOWPATH_PROBABILITY;
35 39
36 /** 40 /**
37 * Directive for the compiler to discontinue compilation at this code position and instead 41 * Directive for the compiler to discontinue compilation at this code position and instead
38 * insert a transfer to the interpreter. 42 * insert a transfer to the interpreter.
39 */ 43 */
61 public static <T> T interpreterOnly(Callable<T> callable) throws Exception { 65 public static <T> T interpreterOnly(Callable<T> callable) throws Exception {
62 return callable.call(); 66 return callable.call();
63 } 67 }
64 68
65 /** 69 /**
66 * Directive for the compiler that the current path has a very low probability to be executed. 70 * Injects a probability for the given condition into the probability information of the
67 */ 71 * immediately succeeding branch instruction for the condition. The probability must be a value
68 public static void slowpath() { 72 * between 0.0 and 1.0 (inclusive). The condition should not be a combined condition.
69 injectBranchProbability(SLOWPATH_PROBABILITY); 73 *
70 } 74 * Example usage immediately before an if statement (it specifies that the likelihood for a to
71 75 * be greater than b is 90%):
72 /** 76 *
73 * Injects a probability for the current path into the probability information of the 77 * <code>
74 * immediately preceeding branch instruction. 78 * if (injectBranchProbability(0.9, a > b)) {
79 * // ...
80 * }
81 * </code>
82 *
83 * Example usage for a combined condition (it specifies that the likelihood for a to be greater
84 * than b is 90% and under the assumption that this is true, the likelihood for a being 0 is
85 * 10%):
86 *
87 * <code>
88 * if (injectBranchProbability(0.9, a > b) && injectBranchProbability(0.1, a == 0)) {
89 * // ...
90 * }
91 * </code>
92 *
93 * There are predefined constants for commonly used probabilities (see
94 * {@link #LIKELY_PROBABILITY} , {@link #UNLIKELY_PROBABILITY}, {@link #SLOWPATH_PROBABILITY},
95 * {@link #FASTPATH_PROBABILITY} ).
75 * 96 *
76 * @param probability the probability value between 0.0 and 1.0 that should be injected 97 * @param probability the probability value between 0.0 and 1.0 that should be injected
77 */ 98 */
78 public static void injectBranchProbability(double probability) { 99 public static boolean injectBranchProbability(double probability, boolean condition) {
79 assert probability >= 0.0 && probability <= 1.0; 100 assert probability >= 0.0 && probability <= 1.0;
101 return condition;
80 } 102 }
81 103
82 /** 104 /**
83 * Bails out of a compilation (e.g., for guest language features that should never be compiled). 105 * Bails out of a compilation (e.g., for guest language features that should never be compiled).
84 * 106 *