Re: RISC-V: Support XTheadVector extensions

["juzhe.zhong@rivai.ai" <juzhe.zhong@rivai.ai>]

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Ok. I just read the theadvector extension.

https://github.com/T-head-Semi/thead-extension-spec/blob/master/xtheadvector.adoc 

Theadvector is not custom extension. Just a uarch to disable some of the RVV1.0 extension
Theadvector can be considered as subextension of 'V' extension with disabling some of the
instructions and adding some new thead vector target load/store (This is another story).

So, for disabling the instruction that theadvector doesn't support. 
You don't need to touch such many codes.

Here is a much simpler approach to do (I think it's definitely working):
1. Don't change any codes in vector.md and keep GCC generates ASM with "th." prefix.
2. Add !TARGET_THEADVECTOR into vector-iterator.md to disable the mode you don't want.
For example , theadvector doesn't support fractional vector.

Then it's pretty simple:

RVVMF2SI "TARGET_VECTOR && !TARGET_THEADVECTOR".

3. Remove all the tests you add in this patch.
4. You can add theadvector specific load/store for example, th.vlb instructions they are allowed.
5. Modify binutils, and make th.vmulh.vv as the pseudo instruction of vmulh.vv
6. So with compile option "-S", you will still see ASM as  "vmulh.vv". but with objdump, you will see th.vmulh.vv.

After this change, you can send V2, then I can continue to review on GCC-15.

Thanks.



juzhe.zhong@rivai.ai
 
From: juzhe.zhong@rivai.ai
Date: 2023-11-17 19:39
To: gcc-patches
CC: kito.cheng; kito.cheng; cooper.joshua; Robin Dapp; jeffreyalaw
Subject: RISC-V: Support XTheadVector extensions
90% theadvector extension reusing current RVV 1.0 instructions patterns:
Just change ASM, For example:

@@ -2923,7 +2923,7 @@ (define_insn "*pred_mulh<v_su><mode>_scalar"
 	     (match_operand:VFULLI_D 3 "register_operand"  "vr,vr, vr, vr")] VMULH)
 	  (match_operand:VFULLI_D 2 "vector_merge_operand" "vu, 0, vu,  0")))]
   "TARGET_VECTOR"
-  "vmulh<v_su>.vx\t%0,%3,%z4%p1"
+  "%^vmulh<v_su>.vx\t%0,%3,%z4%p1"
   [(set_attr "type" "vimul")
    (set_attr "mode" "<MODE>")])
+  if (letter == '^')
+    {
+      if (TARGET_XTHEADVECTOR)
+	fputs ("th.", file);
+      return;
+    }

For almost all patterns, you just simply append "th." in the ASM prefix.
like change "vmulh.vv" -> "th.vmulh.vv"

Almost all theadvector instructions are not new features,  all same as RVV1.0.
Why do you invent the such ISA doesn't include any features that RVV1.0 doesn't satisfy ?

I am not explicitly object this patch. But I should know the reason.

Btw, stage 1 will close soon.  So I will review this patch on GCC-15 as long as all other RISC-V maintainers agree.




juzhe.zhong@rivai.ai