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changeset 13946:28b59501c7b2

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Documentation for jump emission logic.
author Roland Schatz <roland.schatz@oracle.com>
date Thu, 13 Feb 2014 11:18:11 +0100
parents 285d38e44ae5
children 1ea1566100bf
files graal/com.oracle.graal.lir.amd64/src/com/oracle/graal/lir/amd64/AMD64ControlFlow.java
diffstat 1 files changed, 8 insertions(+), 0 deletions(-) [+]
line wrap: on
line diff
--- a/graal/com.oracle.graal.lir.amd64/src/com/oracle/graal/lir/amd64/AMD64ControlFlow.java	Wed Feb 12 23:57:22 2014 -0800
+++ b/graal/com.oracle.graal.lir.amd64/src/com/oracle/graal/lir/amd64/AMD64ControlFlow.java	Thu Feb 13 11:18:11 2014 +0100
@@ -76,6 +76,14 @@
 
         @Override
         public void emitCode(CompilationResultBuilder crb, AMD64MacroAssembler masm) {
+            /*
+             * The strategy for emitting jumps is: If either trueDestination or falseDestination is
+             * the successor block, assume the block scheduler did the correct thing and jcc to the
+             * other. Otherwise, we need a jcc followed by a jmp. Use the branch probability to make
+             * sure it is more likely to branch on the jcc (= less likely to execute both the jcc
+             * and the jmp instead of just the jcc). In the case of loops, that means the jcc is the
+             * back-edge.
+             */
             if (crb.isSuccessorEdge(trueDestination)) {
                 jcc(masm, true, falseDestination);
             } else if (crb.isSuccessorEdge(falseDestination)) {