[PATCH][committed] aarch64: Remove redundant zero-extends with LDAR

[Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>]

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Hi all,

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.
Pushing to trunk.
Thanks,
Kyrill

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.

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diff --git a/gcc/config/aarch64/atomics.md b/gcc/config/aarch64/atomics.md
index 904870033621598da3c12138e4287083dff6ea3a..bc95f6d9d15f190a3e33704b4def2860d5f339bd 100644
--- a/gcc/config/aarch64/atomics.md
+++ b/gcc/config/aarch64/atomics.md
@@ -640,6 +640,23 @@ (define_insn_and_split "atomic_nand_fetch<mode>"
   }
 )
 
+(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 0000000000000000000000000000000000000000..60b0717271c32d1fcc87358cfbaf2ed6f23fa382
--- /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]+} } } */