1.1 --- a/src/cpu/x86/vm/vm_version_x86.cpp Mon Oct 20 16:37:02 2014 -0400
1.2 +++ b/src/cpu/x86/vm/vm_version_x86.cpp Fri Oct 17 15:35:25 2014 -0700
1.3 @@ -873,14 +873,19 @@
1.4 if (supports_bmi1()) {
1.5 // tzcnt does not require VEX prefix
1.6 if (FLAG_IS_DEFAULT(UseCountTrailingZerosInstruction)) {
1.7 - UseCountTrailingZerosInstruction = true;
1.8 + if (!UseBMI1Instructions && !FLAG_IS_DEFAULT(UseBMI1Instructions)) {
1.9 + // Don't use tzcnt if BMI1 is switched off on command line.
1.10 + UseCountTrailingZerosInstruction = false;
1.11 + } else {
1.12 + UseCountTrailingZerosInstruction = true;
1.13 + }
1.14 }
1.15 } else if (UseCountTrailingZerosInstruction) {
1.16 warning("tzcnt instruction is not available on this CPU");
1.17 FLAG_SET_DEFAULT(UseCountTrailingZerosInstruction, false);
1.18 }
1.19
1.20 - // BMI instructions use an encoding with VEX prefix.
1.21 + // BMI instructions (except tzcnt) use an encoding with VEX prefix.
1.22 // VEX prefix is generated only when AVX > 0.
1.23 if (supports_bmi1() && supports_avx()) {
1.24 if (FLAG_IS_DEFAULT(UseBMI1Instructions)) {
