xtensa: Improve constant synthesis for both integer and floating-point

This patch revises the previous implementation of constant synthesis.

First, changed to use define_split machine description pattern and to run
after reload pass, in order not to interfere some optimizations such as
the loop invariant motion.

Second, not only integer but floating-point is subject to processing.

Third, several new synthesis patterns - when the constant cannot fit into
a "MOVI Ax, simm12" instruction, but:

I.   can be represented as a power of two minus one (eg. 32767, 65535 or
     0x7fffffffUL)
       => "MOVI(.N) Ax, -1" + "SRLI Ax, Ax, 1 ... 31" (or "EXTUI")
II.  is between -34816 and 34559
       => "MOVI(.N) Ax, -2048 ... 2047" + "ADDMI Ax, Ax, -32768 ... 32512"
III. (existing case) can fit into a signed 12-bit if the trailing zero bits
     are stripped
       => "MOVI(.N) Ax, -2048 ... 2047" + "SLLI Ax, Ax, 1 ... 31"

The above sequences consist of 5 or 6 bytes and have latency of 2 clock cycles,
in contrast with "L32R Ax, <litpool>" (3 bytes and one clock latency, but may
suffer additional one clock pipeline stall and implementation-specific
InstRAM/ROM access penalty) plus 4 bytes of constant value.

In addition, 3-instructions synthesis patterns (8 or 9 bytes, 3 clock latency)
are also provided when optimizing for speed and L32R instruction has
considerable access penalty:

IV.  2-instructions synthesis (any of I ... III) followed by
     "SLLI Ax, Ax, 1 ... 31"
V.   2-instructions synthesis followed by either "ADDX[248] Ax, Ax, Ax"
     or "SUBX8 Ax, Ax, Ax" (multiplying by 3, 5, 7 or 9)

gcc/ChangeLog:

	* config/xtensa/xtensa-protos.h (xtensa_constantsynth):
	New prototype.
	* config/xtensa/xtensa.cc (xtensa_emit_constantsynth,
	xtensa_constantsynth_2insn, xtensa_constantsynth_rtx_SLLI,
	xtensa_constantsynth_rtx_ADDSUBX, xtensa_constantsynth):
	New backend functions that process the abovementioned logic.
	(xtensa_emit_move_sequence): Revert the previous changes.
	* config/xtensa/xtensa.md: New split patterns for integer
	and floating-point, as the frontend part.

gcc/testsuite/ChangeLog:

	* gcc.target/xtensa/constsynth_2insns.c: New.
	* gcc.target/xtensa/constsynth_3insns.c: Ditto.
	* gcc.target/xtensa/constsynth_double.c: Ditto.

6 files changed, 247 insertions, 16 deletions

diff --git a/gcc/config/xtensa/xtensa-protos.h b/gcc/config/xtensa/xtensa-protos.h
index 30e4b54..c2fd750c 100644
--- a/gcc/config/xtensa/xtensa-protos.h
+++ b/gcc/config/xtensa/xtensa-protos.h
@@ -44,6 +44,7 @@ extern int xtensa_expand_block_move (rtx *);
 extern int xtensa_expand_block_set_unrolled_loop (rtx *);
 extern int xtensa_expand_block_set_small_loop (rtx *);
 extern void xtensa_split_operand_pair (rtx *, machine_mode);
+extern int xtensa_constantsynth (rtx, HOST_WIDE_INT);
 extern int xtensa_emit_move_sequence (rtx *, machine_mode);
 extern rtx xtensa_copy_incoming_a7 (rtx);
 extern void xtensa_expand_nonlocal_goto (rtx *);
diff --git a/gcc/config/xtensa/xtensa.cc b/gcc/config/xtensa/xtensa.cc
index 597a36e..3477e98 100644
--- a/gcc/config/xtensa/xtensa.cc
+++ b/gcc/config/xtensa/xtensa.cc
@@ -1037,6 +1037,123 @@ xtensa_split_operand_pair (rtx operands[4], machine_mode mode)
 }
 
 
+/* Try to emit insns to load srcval (that cannot fit into signed 12-bit)
+   into dst with synthesizing a such constant value from a sequence of
+   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);
+
+  if (IN_RANGE (shift, 1, 31))
+    {
+      xtensa_emit_constantsynth (dst, LSHIFTRT, -1, 32 - shift,
+				 gen_op, op_imm);
+      return 1;
+    }
+
+  if (IN_RANGE (srcval, (-2048 - 32768), (2047 + 32512)))
+    {
+      HOST_WIDE_INT imm0, imm1;
+
+      if (srcval < -32768)
+	imm1 = -32768;
+      else if (srcval > 32512)
+	imm1 = 32512;
+      else
+	imm1 = srcval & ~255;
+      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;
+    }
+
+  shift = ctz_hwi (srcval);
+  if (xtensa_simm12b (srcval >> shift))
+    {
+      xtensa_emit_constantsynth (dst, ASHIFT, srcval >> shift, shift,
+				 gen_op, op_imm);
+      return 1;
+    }
+
+  return 0;
+}
+
+static rtx
+xtensa_constantsynth_rtx_SLLI (rtx reg, HOST_WIDE_INT imm)
+{
+  return gen_rtx_ASHIFT (SImode, reg, GEN_INT (imm));
+}
+
+static rtx
+xtensa_constantsynth_rtx_ADDSUBX (rtx reg, HOST_WIDE_INT imm)
+{
+  return imm == 7
+	 ? gen_rtx_MINUS (SImode, gen_rtx_ASHIFT (SImode, reg, GEN_INT (3)),
+			  reg)
+	 : gen_rtx_PLUS (SImode, gen_rtx_ASHIFT (SImode, reg,
+						 GEN_INT (floor_log2 (imm - 1))),
+			 reg);
+}
+
+int
+xtensa_constantsynth (rtx dst, HOST_WIDE_INT srcval)
+{
+  /* No need for synthesizing for what fits into MOVI instruction.  */
+  if (xtensa_simm12b (srcval))
+    return 0;
+
+  /* 2-insns substitution.  */
+  if ((optimize_size || (optimize && xtensa_extra_l32r_costs >= 1))
+      && xtensa_constantsynth_2insn (dst, srcval, NULL, 0))
+    return 1;
+
+  /* 3-insns substitution.  */
+  if (optimize > 1 && !optimize_size && xtensa_extra_l32r_costs >= 2)
+    {
+      int shift, divisor;
+
+      /* 2-insns substitution followed by SLLI.  */
+      shift = ctz_hwi (srcval);
+      if (IN_RANGE (shift, 1, 31) &&
+	  xtensa_constantsynth_2insn (dst, srcval >> shift,
+				      xtensa_constantsynth_rtx_SLLI,
+				      shift))
+	return 1;
+
+      /* 2-insns substitution followed by ADDX[248] or SUBX8.  */
+      if (TARGET_ADDX)
+	for (divisor = 3; divisor <= 9; divisor += 2)
+	  if (srcval % divisor == 0 &&
+	      xtensa_constantsynth_2insn (dst, srcval / divisor,
+					  xtensa_constantsynth_rtx_ADDSUBX,
+					  divisor))
+	    return 1;
+    }
+
+  return 0;
+}
+
+
 /* Emit insns to move operands[1] into operands[0].
    Return 1 if we have written out everything that needs to be done to
    do the move.  Otherwise, return 0 and the caller will emit the move
@@ -1074,22 +1191,6 @@ xtensa_emit_move_sequence (rtx *operands, machine_mode mode)
 
       if (! TARGET_AUTO_LITPOOLS && ! TARGET_CONST16)
 	{
-	  /* Try to emit MOVI + SLLI sequence, that is smaller
-	     than L32R + literal.  */
-	  if (optimize_size && mode == SImode && CONST_INT_P (src)
-	      && register_operand (dst, mode))
-	    {
-	      HOST_WIDE_INT srcval = INTVAL (src);
-	      int shift = ctz_hwi (srcval);
-
-	      if (xtensa_simm12b (srcval >> shift))
-		{
-		  emit_move_insn (dst, GEN_INT (srcval >> shift));
-		  emit_insn (gen_ashlsi3_internal (dst, dst, GEN_INT (shift)));
-		  return 1;
-		}
-	    }
-
 	  src = force_const_mem (SImode, src);
 	  operands[1] = src;
 	}
diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index f6c6be4..d806d43 100644
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -937,6 +937,19 @@
    (set_attr "mode"	"SI")
    (set_attr "length"	"2,2,2,2,2,2,3,3,3,3,6,3,3,3,3,3")])
 
+(define_split
+  [(set (match_operand:SI 0 "register_operand")
+	(match_operand:SI 1 "constantpool_operand"))]
+  "! optimize_debug && reload_completed"
+  [(const_int 0)]
+{
+  rtx x = avoid_constant_pool_reference (operands[1]);
+  if (! CONST_INT_P (x))
+    FAIL;
+  if (! xtensa_constantsynth (operands[0], INTVAL (x)))
+    emit_move_insn (operands[0], x);
+})
+
 ;; 16-bit Integer moves
 
 (define_expand "movhi"
@@ -1139,6 +1152,43 @@
    (set_attr "mode"	"SF")
    (set_attr "length"	"3")])
 
+(define_split
+  [(set (match_operand:SF 0 "register_operand")
+	(match_operand:SF 1 "constantpool_operand"))]
+  "! optimize_debug && reload_completed"
+  [(const_int 0)]
+{
+  int i = 0;
+  rtx x = XEXP (operands[1], 0);
+  long l[2];
+  if (GET_CODE (x) == SYMBOL_REF
+      && CONSTANT_POOL_ADDRESS_P (x))
+    x = get_pool_constant (x);
+  else if (GET_CODE (x) == CONST)
+    {
+      x = XEXP (x, 0);
+      gcc_assert (GET_CODE (x) == PLUS
+		  && GET_CODE (XEXP (x, 0)) == SYMBOL_REF
+		  && CONSTANT_POOL_ADDRESS_P (XEXP (x, 0))
+		  && CONST_INT_P (XEXP (x, 1)));
+      i = INTVAL (XEXP (x, 1));
+      gcc_assert (i == 0 || i == 4);
+      i /= 4;
+      x = get_pool_constant (XEXP (x, 0));
+    }
+  else
+    gcc_unreachable ();
+  if (GET_MODE (x) == SFmode)
+    REAL_VALUE_TO_TARGET_SINGLE (*CONST_DOUBLE_REAL_VALUE (x), l[0]);
+  else if (GET_MODE (x) == DFmode)
+    REAL_VALUE_TO_TARGET_DOUBLE (*CONST_DOUBLE_REAL_VALUE (x), l);
+  else
+    FAIL;
+  x = gen_rtx_REG (SImode, REGNO (operands[0]));
+  if (! xtensa_constantsynth (x, l[i]))
+    emit_move_insn (x, GEN_INT (l[i]));
+})
+
 ;; 64-bit floating point moves
 
 (define_expand "movdf"
diff --git a/gcc/testsuite/gcc.target/xtensa/constsynth_2insns.c b/gcc/testsuite/gcc.target/xtensa/constsynth_2insns.c
new file mode 100644
index 0000000..43c85a2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/xtensa/constsynth_2insns.c
@@ -0,0 +1,44 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+int test_0(void)
+{
+  return 4095;
+}
+
+int test_1(void)
+{
+  return 2147483647;
+}
+
+int test_2(void)
+{
+  return -34816;
+}
+
+int test_3(void)
+{
+  return -2049;
+}
+
+int test_4(void)
+{
+  return 2048;
+}
+
+int test_5(void)
+{
+  return 34559;
+}
+
+int test_6(void)
+{
+  return 43680;
+}
+
+void test_7(int *p)
+{
+  *p = -1432354816;
+}
+
+/* { dg-final { scan-assembler-not "l32r" } } */
diff --git a/gcc/testsuite/gcc.target/xtensa/constsynth_3insns.c b/gcc/testsuite/gcc.target/xtensa/constsynth_3insns.c
new file mode 100644
index 0000000..f3c4a1c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/xtensa/constsynth_3insns.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mextra-l32r-costs=3" } */
+
+int test_0(void)
+{
+  return 134217216;
+}
+
+int test_1(void)
+{
+  return -27604992;
+}
+
+int test_2(void)
+{
+  return -162279;
+}
+
+void test_3(int *p)
+{
+  *p = 192437;
+}
+
+/* { dg-final { scan-assembler-not "l32r" } } */
diff --git a/gcc/testsuite/gcc.target/xtensa/constsynth_double.c b/gcc/testsuite/gcc.target/xtensa/constsynth_double.c
new file mode 100644
index 0000000..890ca50
--- /dev/null
+++ b/gcc/testsuite/gcc.target/xtensa/constsynth_double.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+
+void test(unsigned int count, double array[])
+{
+  unsigned int i;
+  for (i = 0; i < count; ++i)
+    array[i] = 1.0;
+}
+
+/* { dg-final { scan-assembler-not "l32r" } } */