Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-09 Thread Jan Beulich
>>> On 09.07.18 at 10:33, wrote: > Anyway, normally assembler is the one who chooses instruction > encoding. There are different possible views here, and I personally think that while it is a compiler's job to chose optimal encodings, assemblers shouldn't by default alter what the programmer (or

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-09 Thread Jan Beulich
>>> On 09.07.18 at 10:33, wrote: > Anyway, normally assembler is the one who chooses instruction > encoding. There are different possible views here, and I personally think that while it is a compiler's job to chose optimal encodings, assemblers shouldn't by default alter what the programmer (or

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-09 Thread Pavel Machek
On Thu 2018-07-05 09:12:16, Ingo Molnar wrote: > > * Pavel Machek wrote: > > > On Mon 2018-07-02 04:31:54, Jan Beulich wrote: > > > Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing > > > idioms don't require execution bandwidth, as they're being taken care > > > of in the

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-09 Thread Pavel Machek
On Thu 2018-07-05 09:12:16, Ingo Molnar wrote: > > * Pavel Machek wrote: > > > On Mon 2018-07-02 04:31:54, Jan Beulich wrote: > > > Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing > > > idioms don't require execution bandwidth, as they're being taken care > > > of in the

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-05 Thread Ingo Molnar
* Pavel Machek wrote: > On Mon 2018-07-02 04:31:54, Jan Beulich wrote: > > Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing > > idioms don't require execution bandwidth, as they're being taken care > > of in the frontend (through register renaming). Use 32-bit XORs

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-05 Thread Ingo Molnar
* Pavel Machek wrote: > On Mon 2018-07-02 04:31:54, Jan Beulich wrote: > > Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing > > idioms don't require execution bandwidth, as they're being taken care > > of in the frontend (through register renaming). Use 32-bit XORs

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-04 Thread Pavel Machek
On Mon 2018-07-02 04:31:54, Jan Beulich wrote: > Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing > idioms don't require execution bandwidth, as they're being taken care > of in the frontend (through register renaming). Use 32-bit XORs instead. > > Signed-off-by: Jan Beulich

Re: [PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-04 Thread Pavel Machek
On Mon 2018-07-02 04:31:54, Jan Beulich wrote: > Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing > idioms don't require execution bandwidth, as they're being taken care > of in the frontend (through register renaming). Use 32-bit XORs instead. > > Signed-off-by: Jan Beulich

[PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-02 Thread Jan Beulich
Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing idioms don't require execution bandwidth, as they're being taken care of in the frontend (through register renaming). Use 32-bit XORs instead. Signed-off-by: Jan Beulich --- v2: Explain what zeroing idioms are/do in the

[PATCH v2] x86-64: use 32-bit XOR to zero registers

2018-07-02 Thread Jan Beulich
Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms. Zeroing idioms don't require execution bandwidth, as they're being taken care of in the frontend (through register renaming). Use 32-bit XORs instead. Signed-off-by: Jan Beulich --- v2: Explain what zeroing idioms are/do in the