Re: [PATCH 1/2][GCC][AArch64] Implement hint intrinsics for AArch64

[Sudakshina Das <Sudi.Das@arm.com>]

Hi Srinath

On 10/01/19 19:20, Srinath Parvathaneni wrote:
> Hi All,
> 
> This patch implements the ACLE hint intrinsics (nop, yield, wfe, wfi,
> sev and sevl), for AArch64.
> 
> The instructions are documented in the ArmARM[1] and the intrinsics
> specification will be
> published on the Arm website [2].
> 
> [1]
> https://developer.arm.com/docs/ddi0487/latest/arm-architecture-reference-manual-armv8-for-armv8-a-architecture-profile
> [2]
> http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf
> 
> Bootstrapped on aarch64-none-linux-gnu and regression tested on
> aarch64-none-elf with no regressions.
> 
> Ok for trunk? If ok, could someone commit the patch on my behalf, I
> don't have commit rights.
> 
> Thanks,
> Srinath
> 
> gcc/ChangeLog:
> 
> 2019-01-10  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>
> 
> 	* config/aarch64/aarch64.md (yield): New pattern name.
> 	(wfe): Likewise.
> 	(wfi): Likewise.
> 	(sev): Likewise.
> 	(sevl): Likewise.
> 	(UNSPECV_YIELD): New volatile unspec.
> 	(UNSPECV_WFE): Likewise.
> 	(UNSPECV_WFI): Likewise.
> 	(UNSPECV_SEV): Likewise.
> 	(UNSPECV_SEVL): Likewise.
> 	* config/aarch64/aarch64-builtins.c (aarch64_builtins):
> 	AARCH64_SYSHINTOP_BUILTIN_NOP: New builtin.
> 	AARCH64_SYSHINTOP_BUILTIN_YIELD: Likewise.
> 	AARCH64_SYSHINTOP_BUILTIN_WFE: Likewise.
> 	AARCH64_SYSHINTOP_BUILTIN_WFI: Likewise.
> 	AARCH64_SYSHINTOP_BUILTIN_SEV: Likewise.
> 	AARCH64_SYSHINTOP_BUILTIN_SEVL: Likewise.
> 	(aarch64_init_syshintop_builtins): New function.
> 	(aarch64_init_builtins): New call statement.
> 	(aarch64_expand_builtin): New case.
> 	* config/aarch64/arm_acle.h (__nop ): New inline function.
> 	(__yield): Likewise.
> 	(__sev): Likewise.
> 	(__sevl): Likewise.
> 	(__wfi): Likewise.
> 	(__wfe): Likewise.
> 
> gcc/testsuite/ChangeLog:
> 
> 2019-01-10  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>
> 
> 	* gcc.target/aarch64/acle/hint-1.c: New test.
> 	* gcc.target/aarch64/acle/hint-2.c: Likewise.
> 
> 

Thank you for doing this and I am not a maintainer. I have some comments 
bellow:

diff --git a/gcc/config/aarch64/aarch64-builtins.c 
b/gcc/config/aarch64/aarch64-builtins.c
index 
8cced94567008e28b1761ec8771589a3925f2904..d5424f98df1f5c8f206cbded097bdd2dfcd1ca8e 
100644
--- a/gcc/config/aarch64/aarch64-builtins.c
+++ b/gcc/config/aarch64/aarch64-builtins.c
@@ -399,6 +399,13 @@ enum aarch64_builtins
    AARCH64_PAUTH_BUILTIN_AUTIA1716,
    AARCH64_PAUTH_BUILTIN_PACIA1716,
    AARCH64_PAUTH_BUILTIN_XPACLRI,
+  /* System Hint Operation Builtins for AArch64.  */
+  AARCH64_SYSHINTOP_BUILTIN_NOP,
+  AARCH64_SYSHINTOP_BUILTIN_YIELD,
+  AARCH64_SYSHINTOP_BUILTIN_WFE,
+  AARCH64_SYSHINTOP_BUILTIN_WFI,
+  AARCH64_SYSHINTOP_BUILTIN_SEV,
+  AARCH64_SYSHINTOP_BUILTIN_SEVL,
    AARCH64_BUILTIN_MAX
  };

Is there any reason for the naming? They don't seem to be part of any 
extensions? IMHO AARCH64_BUILTIN_NOP, etc looks cleaner and follows 
other builtins which are not part of any extensions.

...
@@ -1395,6 +1436,29 @@ aarch64_expand_builtin (tree exp,
  	}

        return target;
+    case AARCH64_SYSHINTOP_BUILTIN_NOP:
+      emit_insn (GEN_FCN (CODE_FOR_nop) ());
+      return gen_reg_rtx (VOIDmode);
+

Needs a newline before the new case.

...
+(define_insn "yield"
+  [(unspec_volatile [(const_int 0)] UNSPECV_YIELD)]
+  ""
+  "yield"
+  [(set_attr "type" "coproc")]
+)

I don't believe setting the type to coproc in AArch64 is correct. 
Likewise for the other instructions.

...
+/* Test the nop ACLE hint intrinsic */
+/* { dg-do compile } */
+/* { dg-additional-options "-O0" } */
+/* { dg-options "-march=armv8-a" } */
+
+#include "arm_acle.h"
+
+void
+test_hint (void)
+{
+ __nop ();
+}
+
+/* { dg-final { scan-assembler-times "\tnop" 3 } } */

Just curious, why are there 3 nops here?

Thanks
Sudi

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