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Optimizations of When expression with int constants: heuristics from openJDK for decision about using tableswitch/lookupswitch

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Denis Zharkov
2014-04-09 15:36:41 +04:00
committed by Evgeny Gerashchenko
parent a83d600f5e
commit 298742ae69
1 changed files with 14 additions and 4 deletions
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compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java
+14 -4
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@@ -3820,12 +3820,22 @@ The "returned" value of try expression with no finally is either the last expres
i++; i++;
} }
int hi = keys[keys.length - 1]; int nlabels = keys.length;
int hi = keys[nlabels - 1];
int lo = keys[0]; int lo = keys[0];
long emptyCells = ((long) hi - (long) lo + 1) - keys.length;
boolean useTableSwitch = keys.length > 0 && /*
10L * emptyCells <= (long) keys.length; // less then 10% of empty cells * Heuristic estimation if it's better to use tableswitch or lookupswitch.
* From OpenJDK sources
*/
long table_space_cost = 4 + ((long) hi - lo + 1); // words
long table_time_cost = 3; // comparisons
long lookup_space_cost = 3 + 2 * (long) nlabels;
long lookup_time_cost = nlabels;
boolean useTableSwitch = nlabels > 0 &&
table_space_cost + 3 * table_time_cost <=
lookup_space_cost + 3 * lookup_time_cost;
if (!useTableSwitch) { if (!useTableSwitch) {
v.lookupswitch(defaultLabel, keys, labels); v.lookupswitch(defaultLabel, keys, labels);