Mercurial > hg > truffle
comparison src/cpu/x86/vm/vm_version_x86.cpp @ 20555:e48395e6a91b
8059139: It should be possible to explicitly disable usage of TZCNT instr w/ -XX:-UseBMI1Instructions
Reviewed-by: iveresov
author | kvn |
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date | Fri, 17 Oct 2014 15:35:25 -0700 |
parents | 166d744df0de |
children | 7848fc12602b |
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20554:af6ff94a005d | 20555:e48395e6a91b |
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871 | 871 |
872 // Use count trailing zeros instruction if available | 872 // Use count trailing zeros instruction if available |
873 if (supports_bmi1()) { | 873 if (supports_bmi1()) { |
874 // tzcnt does not require VEX prefix | 874 // tzcnt does not require VEX prefix |
875 if (FLAG_IS_DEFAULT(UseCountTrailingZerosInstruction)) { | 875 if (FLAG_IS_DEFAULT(UseCountTrailingZerosInstruction)) { |
876 UseCountTrailingZerosInstruction = true; | 876 if (!UseBMI1Instructions && !FLAG_IS_DEFAULT(UseBMI1Instructions)) { |
877 // Don't use tzcnt if BMI1 is switched off on command line. | |
878 UseCountTrailingZerosInstruction = false; | |
879 } else { | |
880 UseCountTrailingZerosInstruction = true; | |
881 } | |
877 } | 882 } |
878 } else if (UseCountTrailingZerosInstruction) { | 883 } else if (UseCountTrailingZerosInstruction) { |
879 warning("tzcnt instruction is not available on this CPU"); | 884 warning("tzcnt instruction is not available on this CPU"); |
880 FLAG_SET_DEFAULT(UseCountTrailingZerosInstruction, false); | 885 FLAG_SET_DEFAULT(UseCountTrailingZerosInstruction, false); |
881 } | 886 } |
882 | 887 |
883 // BMI instructions use an encoding with VEX prefix. | 888 // BMI instructions (except tzcnt) use an encoding with VEX prefix. |
884 // VEX prefix is generated only when AVX > 0. | 889 // VEX prefix is generated only when AVX > 0. |
885 if (supports_bmi1() && supports_avx()) { | 890 if (supports_bmi1() && supports_avx()) { |
886 if (FLAG_IS_DEFAULT(UseBMI1Instructions)) { | 891 if (FLAG_IS_DEFAULT(UseBMI1Instructions)) { |
887 UseBMI1Instructions = true; | 892 UseBMI1Instructions = true; |
888 } | 893 } |