https://codereview.chromium.org/209933003/diff/1/src/arm64/lithium-codegen-arm64.h
File src/arm64/lithium-codegen-arm64.h (right):
https://codereview.chromium.org/209933003/diff/1/src/arm64/lithium-codegen-arm64.h#newcode385
src/arm64/lithium-codegen-arm64.h:385:
codegen_->masm_->Mov(to_be_pushed_lr, lr);
On 2014/03/24 11:43:28, vincent.belliard.arm wrote:
On 2014/03/24 11:31:26, ulan wrote:
> On 2014/03/24 11:16:59, vincent.belliard.arm wrote:
> > On 2014/03/24 11:09:25, ulan wrote:
> > > to_be_pushed_lr is ip0, how do we guarantee that this doesn't
get
clobbered
> > from
> > > this point until the StoreRegistersStateStub gets control?
> >
> > This register is reserved by the UseScratchRegisterScope so it
cannot be
used
> by
> > the call (which will use the next register: ip1).
> >
> > After the call, we jump directly to the stub code (which has its
own
context)
> > which starts also by a UseScratchRegisterScope which also reserves
> > to_be_pushed_lr.
> Right, and what if the ip0 is not available in the current scope
because it
was
> already reserved before PushSafepointRegistersScope?
In debug, Acquire checks that the register is available. If each
instruction
which use a PushSafepointRegistersScope is used by the at least one
test (I hope
all are used) and if the tests are run in debug, it will ensure that
the
register will be available.
In release, the register could be unavailable and still acquired (no
test is
done during acquire). If it's not available, we will clobber it.
However, it
doesn't matter because as we enter PushSafepointRegistersScope, only
the
safepoint registers must be saved and ip0, ip1 can be cloberred.
OK, thank you for explanation. I went through the call sites of
PushSafepointRegistersScope, and they seem safe to me. Since
Acquire(reg) is unsafe in general case, let's rename it to UnsafeAcquire
and add a comment there explaining when one can use it.
https://codereview.chromium.org/209933003/diff/1/src/arm64/macro-assembler-arm64.h
File src/arm64/macro-assembler-arm64.h (right):
https://codereview.chromium.org/209933003/diff/1/src/arm64/macro-assembler-arm64.h#newcode2218
src/arm64/macro-assembler-arm64.h:2218: Register Acquire(const Register&
reg) {
Please rename to UnsafeAcquire or something similar.
https://codereview.chromium.org/209933003/diff/1/src/arm64/macro-assembler-arm64.h#newcode2222
src/arm64/macro-assembler-arm64.h:2222: return
AcquireFixed(availablefp_, reg);
It is not used and unsafe, please remove.
https://codereview.chromium.org/209933003/
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