[9] RFR(S): 8075798: Allow ADLC register class to depend on runtime conditions also for cisc-spillable classes

[Zoltán Majó]

Hi,


please review the following patch.

Bug: https://bugs.openjdk.java.net/browse/JDK-8075798


Problem: In .ad files, it is difficult to have register classes that 
depend on runtime conditions. JDK-7090968 partially solves the problem, 
but it does not work in cases when not only a register mask, but also a
"stack mask" is generated for a register class (i.e., the register class 
is "cisc-spillable"). (If a stack mask is needed for classes dependant 
on runtime conditions, the assert on line 155 in 
src/share/vm/adlc/output_c.cpp fails.)

The goal of this enhancement is to extend ADLC parsing to allow 
cisc-spillable register classes to depend on runtime conditions.


Solution: Introduce a new register class, reg_class_dynamic. The new 
register class is used with the following syntax:

reg_class_dynamic actual_dflt_reg(dflt_reg, low_reg, %{ 
VM_Version::has_vfp3_32() }% );

where dflt_reg and low_reg are two existing "static" register classes 
and actual_dflt_reg is the newly defined register class.

The functionality of the actual_dflt_reg defined with reg_class_dynamic 
is equivalent to the existing syntax

reg_class actual_dflt_reg %{
     if (VM_Version::has_vfp3_32()) {
         return DFLT_REG_mask();
     } else {
         return DFLT_LOW_REG_mask();
     }
}

The difference between the two register class declarations is that the 
declaration with reg_class_dynamic allows the declared register class to 
be "cisc-spillable", whereas a declaration with reg_class does not. The 
code attached to a reg_class can be, however, more elaborate than a 
simple if-then-else allowed with reg_class_dynamic.


Webrev: http://cr.openjdk.java.net/~zmajo/8075798/webrev.00/


Testing:
- JPRT testing on all supported platforms
- manual testing on x86_64 with a .ad file that includes a reg_class 
definition with a code snippet as well as a reg_class_dynamic definition.


Thank you and best regards,


Zoltan