[PATCH][GCC][Arm] Add pattern for bswap + rotate -> rev16 [Bug 108933]

[Matthieu Longo <matthieu.longo@arm.com>]

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rev16 pattern was not recognised anymore as a change in the bswap tree
pass was introducing a new GIMPLE form, not recognized by the assembly
final transformation pass.

More details in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108933

gcc/ChangeLog:

         PR target/108933
         * config/arm/arm.md (*arm_rev16si2_alt3): new pattern to convert
           a bswap + rotate by 16 bits into rev16

gcc/testsuite/ChangeLog:

         PR target/108933
         * gcc.target/arm/rev16.c: Moved to...
         * gcc.target/arm/rev16_1.c: ...here.
         * gcc.target/arm/rev16_2.c: New test to check that rev16 is
           emitted.

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diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 4a98f2d7b6251da940806b26d4c310a7f7af927b..330c0a5ce2926439760466746a68fd5f6c5b1b09 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -12601,6 +12601,18 @@
    (set_attr "type" "rev")]
 )
 
+;; Similar pattern to match (rotate (bswap) 16)
+(define_insn "*arm_rev16si2_alt3"
+  [(set (match_operand:SI 0 "register_operand" "=l,r")
+        (rotate:SI (bswap:SI (match_operand:SI 1 "register_operand" "l,r"))
+                     (const_int 16)))]
+  "arm_arch6"
+  "rev16\\t%0, %1"
+  [(set_attr "arch" "t,32")
+   (set_attr "length" "2,4")
+   (set_attr "type" "rev")]
+)
+
 (define_expand "arm_rev16si2"
   [(set (match_operand:SI 0 "s_register_operand")
 	(bswap:SI (match_operand:SI 1 "s_register_operand")))]
diff --git a/gcc/testsuite/gcc.target/arm/rev16.c b/gcc/testsuite/gcc.target/arm/rev16_1.c
similarity index 100%
rename from gcc/testsuite/gcc.target/arm/rev16.c
rename to gcc/testsuite/gcc.target/arm/rev16_1.c
diff --git a/gcc/testsuite/gcc.target/arm/rev16_2.c b/gcc/testsuite/gcc.target/arm/rev16_2.c
new file mode 100644
index 0000000000000000000000000000000000000000..90213f9b49f45340ced4f29c31446971dbc88ecd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/rev16_2.c
@@ -0,0 +1,20 @@
+/* { dg-options "-O2" } */
+/* { dg-do compile } */
+
+typedef unsigned int __u32;
+
+__u32
+__rev16_32_alt (__u32 x)
+{
+  return (((__u32)(x) & (__u32)0xff00ff00UL) >> 8)
+         | (((__u32)(x) & (__u32)0x00ff00ffUL) << 8);
+}
+
+__u32
+__rev16_32 (__u32 x)
+{
+  return (((__u32)(x) & (__u32)0x00ff00ffUL) << 8)
+         | (((__u32)(x) & (__u32)0xff00ff00UL) >> 8);
+}
+
+/* { dg-final { scan-assembler-times {rev16\tr[0-9]+, r[0-9]+} 2 } } */
\ No newline at end of file