xtensa: constantsynth: Make try to find shorter instruction

This patch allows the constant synthesis to choose shorter instruction
if possible.

    /* example */
    int test(void) {
      return 128 << 8;
    }

    ;; before
    test:
	movi	a2, 0x100
	addmi	a2, a2, 0x7f00
	ret.n

    ;; after
    test:
	movi.n	a2, 1
	slli	a2, a2, 15
	ret.n

When the Code Density Option is configured, the latter is one byte smaller
than the former.

gcc/ChangeLog:

	* config/xtensa/xtensa.cc (xtensa_emit_constantsynth): Remove.
	(xtensa_constantsynth_2insn): Change to try all three synthetic
	methods and to use the one that fits the immediate value of
	the seed into a Narrow Move Immediate instruction "MOVI.N"
	when the Code Density Option is configured.

diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc
index 13f2b2b..9433745 100644 (file)
--- a/gcc/config/xtensa/xtensa.cc
+++ b/gcc/config/xtensa/xtensa.cc
@@ -1035,35 +1035,35 @@ xtensa_split_operand_pair (rtx operands[4], machine_mode mode)
    load-immediate / arithmetic ones, instead of a L32R instruction
    (plus a constant in litpool).  */
 
-static void
-xtensa_emit_constantsynth (rtx dst, enum rtx_code code,
-                          HOST_WIDE_INT imm0, HOST_WIDE_INT imm1,
-                          rtx (*gen_op)(rtx, HOST_WIDE_INT),
-                          HOST_WIDE_INT imm2)
-{
-  gcc_assert (REG_P (dst));
-  emit_move_insn (dst, GEN_INT (imm0));
-  emit_move_insn (dst, gen_rtx_fmt_ee (code, SImode,
-                                      dst, GEN_INT (imm1)));
-  if (gen_op)
-    emit_move_insn (dst, gen_op (dst, imm2));
-}
-
 static int
 xtensa_constantsynth_2insn (rtx dst, HOST_WIDE_INT srcval,
                            rtx (*gen_op)(rtx, HOST_WIDE_INT),
                            HOST_WIDE_INT op_imm)
 {
-  int shift = exact_log2 (srcval + 1);
+  HOST_WIDE_INT imm = INT_MAX;
+  rtx x = NULL_RTX;
+  int shift;
 
+  gcc_assert (REG_P (dst));
+
+  shift = exact_log2 (srcval + 1);
   if (IN_RANGE (shift, 1, 31))
     {
-      xtensa_emit_constantsynth (dst, LSHIFTRT, -1, 32 - shift,
-                                gen_op, op_imm);
-      return 1;
+      imm = -1;
+      x = gen_lshrsi3 (dst, dst, GEN_INT (32 - shift));
     }
 
-  if (IN_RANGE (srcval, (-2048 - 32768), (2047 + 32512)))
+
+  shift = ctz_hwi (srcval);
+  if ((!x || (TARGET_DENSITY && ! IN_RANGE (imm, -32, 95)))
+      && xtensa_simm12b (srcval >> shift))
+    {
+      imm = srcval >> shift;
+      x = gen_ashlsi3 (dst, dst, GEN_INT (shift));
+    }
+
+  if ((!x || (TARGET_DENSITY && ! IN_RANGE (imm, -32, 95)))
+      && IN_RANGE (srcval, (-2048 - 32768), (2047 + 32512)))
     {
       HOST_WIDE_INT imm0, imm1;
 
@@ -1076,19 +1076,19 @@ xtensa_constantsynth_2insn (rtx dst, HOST_WIDE_INT srcval,
       imm0 = srcval - imm1;
       if (TARGET_DENSITY && imm1 < 32512 && IN_RANGE (imm0, 224, 255))
        imm0 -= 256, imm1 += 256;
-      xtensa_emit_constantsynth (dst, PLUS, imm0, imm1, gen_op, op_imm);
-       return 1;
+      imm = imm0;
+      x = gen_addsi3 (dst, dst, GEN_INT (imm1));
     }
 
-  shift = ctz_hwi (srcval);
-  if (xtensa_simm12b (srcval >> shift))
-    {
-      xtensa_emit_constantsynth (dst, ASHIFT, srcval >> shift, shift,
-                                gen_op, op_imm);
-      return 1;
-    }
+  if (!x)
+    return 0;
 
-  return 0;
+  emit_move_insn (dst, GEN_INT (imm));
+  emit_insn (x);
+  if (gen_op)
+    emit_move_insn (dst, gen_op (dst, op_imm));
+
+  return 1;
 }
 
 static rtx