Probe the symbol table for two character strings in native code...

Probe the symbol table for two character strings in native code

All two character string results from adding two strings and from sub string used to be handled in the runtime system as a lookup in the symbol table was done before allocating a new string. The native code for string add and sub string now probes the symbol cache for two character strings to avoid the runtime call. If the result string is not found in the symbol table within a fixed number of probes a new string is just allocated. Newly allocated two character strings are not added to the symbol table immediately.

Committed: http://code.google.com/p/v8/source/detail?r=3842

[Mads Ager (chromium), 2010-02-12 10:24:05]

LGTM

http://codereview.chromium.org/598062/diff/1/2
File src/ia32/codegen-ia32.cc (right):

http://codereview.chromium.org/598062/diff/1/2#newcode9904
src/ia32/codegen-ia32.cc:9904: Label *not_found) {
Label * -> Label*

http://codereview.chromium.org/598062/diff/1/2#newcode9910
src/ia32/codegen-ia32.cc:9910: Label not_aray_index;
not_aray_index -> not_array_index

http://codereview.chromium.org/598062/diff/1/2#newcode9929
src/ia32/codegen-ia32.cc:9929: __ shl(c2, 8);
kBitsInByte?

http://codereview.chromium.org/598062/diff/1/2#newcode9952
src/ia32/codegen-ia32.cc:9952: // chars:        two character string (al first
char and ah second char)
al and ah -> byte 0 and byte 1?  Nothing guarentees that the register will be
eax, right?

http://codereview.chromium.org/598062/diff/1/2#newcode9985
src/ia32/codegen-ia32.cc:9985: // If length is not 2 the string is no a
candidate.
no -> not

http://codereview.chromium.org/598062/diff/1/2#newcode10000
src/ia32/codegen-ia32.cc:10000: __ push(scratch);  // Save candidate.
On the fast path we do push,pop,push,pop - can we make another entry label for
pop_next_probe[i]?  That should be the right fall-through label, so I think it
would be easy to avoid the extra push/pop?

http://codereview.chromium.org/598062/diff/1/3
File src/ia32/codegen-ia32.h (right):

http://codereview.chromium.org/598062/diff/1/3#newcode775
src/ia32/codegen-ia32.h:775: void
Generate2CharacterSymbolTableProbe(MacroAssembler* masm,
2 -> Two?

http://codereview.chromium.org/598062/diff/1/3#newcode781
src/ia32/codegen-ia32.h:781: Label *not_found);
Label * -> Label*

[Søren Thygesen Gjesse, 2010-02-12 11:41:32]

http://codereview.chromium.org/598062/diff/1/2
File src/ia32/codegen-ia32.cc (right):

http://codereview.chromium.org/598062/diff/1/2#newcode9904
src/ia32/codegen-ia32.cc:9904: Label *not_found) {
On 2010/02/12 10:24:05, Mads Ager wrote:
> Label * -> Label*
> 

Done.

http://codereview.chromium.org/598062/diff/1/2#newcode9910
src/ia32/codegen-ia32.cc:9910: Label not_aray_index;
On 2010/02/12 10:24:05, Mads Ager wrote:
> not_aray_index -> not_array_index

Done.

http://codereview.chromium.org/598062/diff/1/2#newcode9929
src/ia32/codegen-ia32.cc:9929: __ shl(c2, 8);
On 2010/02/12 10:24:05, Mads Ager wrote:
> kBitsInByte?

Done (kBitsPerByte).

http://codereview.chromium.org/598062/diff/1/2#newcode9952
src/ia32/codegen-ia32.cc:9952: // chars:        two character string (al first
char and ah second char)
On 2010/02/12 10:24:05, Mads Ager wrote:
> al and ah -> byte 0 and byte 1?  Nothing guarentees that the register will be
> eax, right?

Done.

http://codereview.chromium.org/598062/diff/1/2#newcode9985
src/ia32/codegen-ia32.cc:9985: // If length is not 2 the string is no a
candidate.
On 2010/02/12 10:24:05, Mads Ager wrote:
> no -> not

Done.

http://codereview.chromium.org/598062/diff/1/2#newcode10000
src/ia32/codegen-ia32.cc:10000: __ push(scratch);  // Save candidate.
On 2010/02/12 10:24:05, Mads Ager wrote:
> On the fast path we do push,pop,push,pop - can we make another entry label for
> pop_next_probe[i]?  That should be the right fall-through label, so I think it
> would be easy to avoid the extra push/pop?

Good point. Ended up pushing mask and used that as a temporary to keep the
candidate unchanged in a register.

http://codereview.chromium.org/598062/diff/1/3
File src/ia32/codegen-ia32.h (right):

http://codereview.chromium.org/598062/diff/1/3#newcode775
src/ia32/codegen-ia32.h:775: void
Generate2CharacterSymbolTableProbe(MacroAssembler* masm,
On 2010/02/12 10:24:05, Mads Ager wrote:
> 2 -> Two?

Done.

http://codereview.chromium.org/598062/diff/1/3#newcode781
src/ia32/codegen-ia32.h:781: Label *not_found);
On 2010/02/12 10:24:05, Mads Ager wrote:
> Label * -> Label*

Done.