Hi All,

Similar to the 1/2 patch but adds additional back-end specific folding for if
the register sequence was created as a result of RTL optimizations.

Concretely:

#include <arm_neon.h>

unsigned int foor (uint32x4_t x)
{
    return x[1] >> 16;
}

generates:

foor:
        umov    w0, v0.h[3]
        ret

instead of

foor:
        umov    w0, v0.s[1]
        lsr     w0, w0, 16
        ret

Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

	* config/aarch64/aarch64.md (*<optab>si3_insn_uxtw): Split SHIFT into
	left and right ones.
	* config/aarch64/constraints.md (Usl): New.
	* config/aarch64/iterators.md (SHIFT_NL, LSHIFTRT): New.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/shift-read.c: New test.

--- inline copy of patch -- 
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index c333fb1f72725992bb304c560f1245a242d5192d..6aa1fb4be003f2027d63ac69fd314c2bbc876258 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -5493,7 +5493,7 @@ (define_insn "*rol<mode>3_insn"
 ;; zero_extend version of shifts
 (define_insn "*<optab>si3_insn_uxtw"
   [(set (match_operand:DI 0 "register_operand" "=r,r")
-	(zero_extend:DI (SHIFT_no_rotate:SI
+	(zero_extend:DI (SHIFT_arith:SI
 	 (match_operand:SI 1 "register_operand" "r,r")
 	 (match_operand:QI 2 "aarch64_reg_or_shift_imm_si" "Uss,r"))))]
   ""
@@ -5528,6 +5528,60 @@ (define_insn "*rolsi3_insn_uxtw"
   [(set_attr "type" "rotate_imm")]
 )
 
+(define_insn "*<optab>si3_insn2_uxtw"
+  [(set (match_operand:DI 0 "register_operand" "=r,?r,r")
+	(zero_extend:DI (LSHIFTRT:SI
+	 (match_operand:SI 1 "register_operand" "w,r,r")
+	 (match_operand:QI 2 "aarch64_reg_or_shift_imm_si" "Usl,Uss,r"))))]
+  ""
+  {
+    switch (which_alternative)
+    {
+      case 0:
+	{
+	  machine_mode dest, vec_mode;
+	  int val = INTVAL (operands[2]);
+	  int size = 32 - val;
+	  if (size == 16)
+	    dest = HImode;
+	  else if (size == 8)
+	    dest = QImode;
+	  else
+	    gcc_unreachable ();
+
+	  /* Get nearest 64-bit vector mode.  */
+	  int nunits = 64 / size;
+	  auto vector_mode
+	    = mode_for_vector (as_a <scalar_mode> (dest), nunits);
+	  if (!vector_mode.exists (&vec_mode))
+	    gcc_unreachable ();
+	  operands[1] = gen_rtx_REG (vec_mode, REGNO (operands[1]));
+	  operands[2] = gen_int_mode (val / size, SImode);
+
+	  /* Ideally we just call aarch64_get_lane_zero_extend but reload gets
+	     into a weird loop due to a mov of w -> r being present most time
+	     this instruction applies.  */
+	  switch (dest)
+	  {
+	    case QImode:
+	      return "umov\\t%w0, %1.b[%2]";
+	    case HImode:
+	      return "umov\\t%w0, %1.h[%2]";
+	    default:
+	      gcc_unreachable ();
+	  }
+	}
+      case 1:
+	return "<shift>\\t%w0, %w1, %2";
+      case 2:
+	return "<shift>\\t%w0, %w1, %w2";
+      default:
+	gcc_unreachable ();
+      }
+  }
+  [(set_attr "type" "neon_to_gp,bfx,shift_reg")]
+)
+
 (define_insn "*<optab><mode>3_insn"
   [(set (match_operand:SHORT 0 "register_operand" "=r")
 	(ASHIFT:SHORT (match_operand:SHORT 1 "register_operand" "r")
diff --git a/gcc/config/aarch64/constraints.md b/gcc/config/aarch64/constraints.md
index ee7587cca1673208e2bfd6b503a21d0c8b69bf75..470510d691ee8589aec9b0a71034677534641bea 100644
--- a/gcc/config/aarch64/constraints.md
+++ b/gcc/config/aarch64/constraints.md
@@ -166,6 +166,14 @@ (define_constraint "Uss"
   (and (match_code "const_int")
        (match_test "(unsigned HOST_WIDE_INT) ival < 32")))
 
+(define_constraint "Usl"
+  "@internal
+  A constraint that matches an immediate shift constant in SImode that has an
+  exact mode available to use."
+  (and (match_code "const_int")
+       (and (match_test "satisfies_constraint_Uss (op)")
+	    (match_test "(32 - ival == 8) || (32 - ival == 16)"))))
+
 (define_constraint "Usn"
  "A constant that can be used with a CCMN operation (once negated)."
  (and (match_code "const_int")
diff --git a/gcc/config/aarch64/iterators.md b/gcc/config/aarch64/iterators.md
index e904407b2169e589b7007ff966b2d9347a6d0fd2..bf16207225e3a4f1f20ed6f54321bccbbf15d73f 100644
--- a/gcc/config/aarch64/iterators.md
+++ b/gcc/config/aarch64/iterators.md
@@ -2149,8 +2149,11 @@ (define_mode_attr sve_lane_pair_con [(VNx8HF "y") (VNx4SF "x")])
 ;; This code iterator allows the various shifts supported on the core
 (define_code_iterator SHIFT [ashift ashiftrt lshiftrt rotatert rotate])
 
-;; This code iterator allows all shifts except for rotates.
-(define_code_iterator SHIFT_no_rotate [ashift ashiftrt lshiftrt])
+;; This code iterator allows arithmetic shifts
+(define_code_iterator SHIFT_arith [ashift ashiftrt])
+
+;; Singleton code iterator for only logical right shift.
+(define_code_iterator LSHIFTRT [lshiftrt])
 
 ;; This code iterator allows the shifts supported in arithmetic instructions
 (define_code_iterator ASHIFT [ashift ashiftrt lshiftrt])
diff --git a/gcc/testsuite/gcc.target/aarch64/shift-read.c b/gcc/testsuite/gcc.target/aarch64/shift-read.c
new file mode 100644
index 0000000000000000000000000000000000000000..e6e355224c96344fe1cdabd6b0d3d5d609cd95bd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/shift-read.c
@@ -0,0 +1,85 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-O2" } */
+/* { dg-final { check-function-bodies "**" "" "" { target { le } } } } */
+
+#include <arm_neon.h>
+
+/*
+** foor:
+** 	umov	w0, v0.h\[3\]
+** 	ret
+*/
+unsigned int foor (uint32x4_t x)
+{
+    return x[1] >> 16;
+}
+
+/*
+** fool:
+** 	umov	w0, v0.s\[1\]
+** 	lsl	w0, w0, 16
+** 	ret
+*/
+unsigned int fool (uint32x4_t x)
+{
+    return x[1] << 16;
+}
+
+/*
+** foor2:
+** 	umov	w0, v0.h\[7\]
+** 	ret
+*/
+unsigned short foor2 (uint32x4_t x)
+{
+    return x[3] >> 16;
+}
+
+/*
+** fool2:
+** 	fmov	w0, s0
+** 	lsl	w0, w0, 16
+** 	ret
+*/
+unsigned int fool2 (uint32x4_t x)
+{
+    return x[0] << 16;
+}
+
+typedef int v4si __attribute__ ((vector_size (16)));
+
+/*
+** bar:
+**	addv	s0, v0.4s
+**	fmov	w0, s0
+**	lsr	w1, w0, 16
+**	add	w0, w1, w0, uxth
+**	ret
+*/
+int bar (v4si x)
+{
+  unsigned int sum = vaddvq_s32 (x);
+  return (((uint16_t)(sum & 0xffff)) + ((uint32_t)sum >> 16));
+}
+
+/*
+** foo:
+** 	lsr	w0, w0, 16
+** 	ret
+*/
+unsigned short foo (unsigned x)
+{
+  return x >> 16;
+}
+
+/*
+** foo2:
+**	...
+** 	umov	w0, v[0-8]+.h\[1\]
+** 	ret
+*/
+unsigned short foo2 (v4si x)
+{
+  int y = x[0] + x[1];
+  return y >> 16;
+}




--