RFR: JDK-8241503: C2: Share MacroAssembler between mach nodes during code emission

[Dean Long]

On Fri, 3 Nov 2023 01:44:42 GMT, Dean Long <dlong at openjdk.org> wrote:

>> # Description
>> 
>> Please review this PR with a patch to re-use the same C2_MacroAssembler object to emit all instructions in the same compilation unit.
>> 
>> Overall, the change is pretty simple. However, due to the renaming of the variable to access C2_MacroAssembler, from `_masm.` to `masm->`, and also some method prototype changes, the patch became quite large.
>> 
>> # Help Needed for Testing
>> 
>> I don't have access to all platforms necessary to test this. I hope some other folks can help with testing on `S390`, `RISC-V` and `PPC`.
>
> src/hotspot/cpu/x86/gc/z/z_x86_64.ad line 37:
> 
>> 35: #include "gc/z/zBarrierSetAssembler.hpp"
>> 36: 
>> 37: static void z_color(MacroAssembler* masm, const MachNode* node, Register ref) {
> 
> For files already using MacroAssembler& _masm, the only change needed is this at the top:
> 
> undef __
> #define __ _masm.

I guess that doesn't work because different files are concatenated together, causing a conflict if some files expect MacroAssembler *masm.  To reduce the number of changes, couldn't we use MacroAssembler& _masm everywhere?

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PR Review Comment: https://git.openjdk.org/jdk/pull/16484#discussion_r1381098489