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8059139: It should be possible to explicitly disable usage of TZCNT instr w/ -XX:-UseBMI1Instructions

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Reviewed-by: iveresov
This commit is contained in:
Vladimir Kozlov 2014-10-17 15:35:25 -07:00
parent 4b046500b7
commit 44d1787a26
1 changed files with 7 additions and 2 deletions
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9
hotspot/src/cpu/x86/vm/vm_version_x86.cpp
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@ -865,14 +865,19 @@ void VM_Version::get_processor_features() {
if (supports_bmi1()) { if (supports_bmi1()) {
// tzcnt does not require VEX prefix // tzcnt does not require VEX prefix
if (FLAG_IS_DEFAULT(UseCountTrailingZerosInstruction)) { if (FLAG_IS_DEFAULT(UseCountTrailingZerosInstruction)) {
UseCountTrailingZerosInstruction = true; if (!UseBMI1Instructions && !FLAG_IS_DEFAULT(UseBMI1Instructions)) {
// Don't use tzcnt if BMI1 is switched off on command line.
UseCountTrailingZerosInstruction = false;
} else {
UseCountTrailingZerosInstruction = true;
}
} }
} else if (UseCountTrailingZerosInstruction) { } else if (UseCountTrailingZerosInstruction) {
warning("tzcnt instruction is not available on this CPU"); warning("tzcnt instruction is not available on this CPU");
FLAG_SET_DEFAULT(UseCountTrailingZerosInstruction, false); FLAG_SET_DEFAULT(UseCountTrailingZerosInstruction, false);
} }
// BMI instructions use an encoding with VEX prefix. // BMI instructions (except tzcnt) use an encoding with VEX prefix.
// VEX prefix is generated only when AVX > 0. // VEX prefix is generated only when AVX > 0.
if (supports_bmi1() && supports_avx()) { if (supports_bmi1() && supports_avx()) {
if (FLAG_IS_DEFAULT(UseBMI1Instructions)) { if (FLAG_IS_DEFAULT(UseBMI1Instructions)) {