[gcc r13-3130] aarch64: Remove redundant zero-extends with LDAR

[Kyrylo Tkachov <ktkachov@gcc.gnu.org>]

https://gcc.gnu.org/g:33b93ac3f2fb68a2da0d42fd692fe59533f7a84f

commit r13-3130-g33b93ac3f2fb68a2da0d42fd692fe59533f7a84f
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Thu Oct 6 12:09:28 2022 +0100

    aarch64: Remove redundant zero-extends with LDAR
    
    Like other loads in AArch64, the LDARB,LDARH,LDAR instructions clear out the top part of their
    destination register and we can thus avoid having to explicitly zero-extend it.
    We were missing a combine pattern that this patch adds.
    
    For one of the examples in the testcase we generated:
    load_uint8_t_ext_uint16_t:
            adrp    x0, .LANCHOR0
            add     x0, x0, :lo12:.LANCHOR0
            ldarb   w0, [x0]
            and     w0, w0, 255
            ret
    
    but now generate:
    load_uint8_t_ext_uint16_t:
            adrp    x0, .LANCHOR0
            add     x0, x0, :lo12:.LANCHOR0
            ldarb   w0, [x0]
            ret
    
    Bootstrapped and tested on aarch64-none-linux-gnu.
    
    gcc/ChangeLog:
    
            * config/aarch64/atomics.md (*atomic_load<ALLX:mode>_zext<SD_HSDI:mode>):
            New pattern.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/aarch64/ldar_2.c: New test.

Diff:
---
 gcc/config/aarch64/atomics.md             | 17 +++++++++++++++++
 gcc/testsuite/gcc.target/aarch64/ldar_2.c | 27 +++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/gcc/config/aarch64/atomics.md b/gcc/config/aarch64/atomics.md
index 90487003362..bc95f6d9d15 100644
--- a/gcc/config/aarch64/atomics.md
+++ b/gcc/config/aarch64/atomics.md
@@ -640,6 +640,23 @@
   }
 )
 
+(define_insn "*atomic_load<ALLX:mode>_zext<SD_HSDI:mode>"
+  [(set (match_operand:SD_HSDI 0 "register_operand" "=r")
+	(zero_extend:SD_HSDI
+	  (unspec_volatile:ALLX
+	    [(match_operand:ALLX 1 "aarch64_sync_memory_operand" "Q")
+	     (match_operand:SI 2 "const_int_operand")]			;; model
+	   UNSPECV_LDA)))]
+  "GET_MODE_SIZE (<SD_HSDI:MODE>mode) > GET_MODE_SIZE (<ALLX:MODE>mode)"
+  {
+    enum memmodel model = memmodel_from_int (INTVAL (operands[2]));
+    if (is_mm_relaxed (model) || is_mm_consume (model) || is_mm_release (model))
+      return "ldr<ALLX:atomic_sfx>\t%<ALLX:w>0, %1";
+    else
+      return "ldar<ALLX:atomic_sfx>\t%<ALLX:w>0, %1";
+  }
+)
+
 (define_insn "atomic_load<mode>"
   [(set (match_operand:ALLI 0 "register_operand" "=r")
     (unspec_volatile:ALLI
diff --git a/gcc/testsuite/gcc.target/aarch64/ldar_2.c b/gcc/testsuite/gcc.target/aarch64/ldar_2.c
new file mode 100644
index 00000000000..60b0717271c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/ldar_2.c
@@ -0,0 +1,27 @@
+/* Test that the zero-extending patterns for LDAR are used.  */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#include <stdint.h>
+
+uint8_t v_uint8_t;
+uint16_t v_uint16_t;
+uint32_t v_uint32_t;
+uint64_t v_uint64_t;
+
+#define FUNC(FROM, TO)						\
+TO								\
+load_##FROM##_ext_##TO (void)					\
+{								\
+  return __atomic_load_n (&v_##FROM, __ATOMIC_ACQUIRE);		\
+}
+
+FUNC (uint8_t, uint16_t)
+FUNC (uint8_t, uint32_t)
+FUNC (uint8_t, uint64_t)
+FUNC (uint16_t, uint32_t)
+FUNC (uint16_t, uint64_t)
+FUNC (uint32_t, uint64_t)
+
+/* { dg-final { scan-assembler-not {and\tw[0-9+], w[0-9]+, 255} } } */
+/* { dg-final { scan-assembler-not {uxtw\tx[0-9+], w[0-9]+} } } */