MSP430: Implement TARGET_INSN_COST

The length of an insn can be used to calculate its cost, when optimizing
for size. When optimizing for speed, this is a good estimate, since the
cycle cost of an MSP430 instruction increases with its length.

gcc/ChangeLog:

	* config/msp430/msp430.c (TARGET_INSN_COST): Define.
	(msp430_insn_cost): New function.
	* config/msp430/msp430.h (BRANCH_COST): Define.
	(LOGICAL_OP_NON_SHORT_CIRCUIT): Define.

gcc/testsuite/ChangeLog:

	* gcc.target/msp430/rtx-cost-O3-default.c: New test.
	* gcc.target/msp430/rtx-cost-O3-f5series.c: New test.
	* gcc.target/msp430/rtx-cost-Os-default.c: New test.
	* gcc.target/msp430/rtx-cost-Os-f5series.c: New test.

Author: jozefl-mitto

gcc/config/msp430/msp430.c

@@ -1181,11 +1181,6 @@ msp430_memory_move_cost (machine_mode mode ATTRIBUTE_UNUSED,
   return 2 * cost;
 }
 
-/* BRANCH_COST
-   Changing from the default of 1 doesn't affect code generation, presumably
-   because there are no conditional move insns - when a condition is involved,
-   the only option is to use a cbranch.  */
-
 /* For X, which must be a MEM RTX, return TRUE if it is an indirect memory
    reference, @Rn or @Rn+.  */
 static bool
@@ -1650,6 +1645,26 @@ msp430_rtx_costs (rtx x,
       return false;
     }
 }
+
+#undef TARGET_INSN_COST
+#define TARGET_INSN_COST msp430_insn_cost
+
+static int
+msp430_insn_cost (rtx_insn *insn, bool speed ATTRIBUTE_UNUSED)
+{
+  if (recog_memoized (insn) < 0)
+    return 0;
+
+  /* The returned cost must be relative to COSTS_N_INSNS (1). An insn with a
+     length of 2 bytes is the smallest possible size and so must be equivalent
+     to COSTS_N_INSNS (1).  */
+  return COSTS_N_INSNS (get_attr_length (insn) / 2);
+
+  /* FIXME Add more detailed costs when optimizing for speed.
+     For now the length of the instruction is a good approximiation and roughly
+     correlates with cycle cost.  */
+}
+
 
 /* Function Entry and Exit */
 

gcc/config/msp430/msp430.h

@@ -243,6 +243,14 @@ extern const char *msp430_get_linker_devices_include_path (int, const char **);
 #define HAS_LONG_COND_BRANCH		0
 #define HAS_LONG_UNCOND_BRANCH		0
 
+/* The cost of a branch sequence is roughly 3 "cheap" instructions.  */
+#define BRANCH_COST(speed_p, predictable_p) 3
+
+/* Override the default BRANCH_COST heuristic to indicate that it is preferable
+   to retain short-circuit operations, this results in significantly better
+   codesize and performance.  */
+#define LOGICAL_OP_NON_SHORT_CIRCUIT 0
+
 #define LOAD_EXTEND_OP(M)		ZERO_EXTEND
 #define WORD_REGISTER_OPERATIONS	1
 

gcc/testsuite/gcc.target/msp430/rtx-cost-O3-default.c

@@ -0,0 +1,42 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+/* Verify the MSP430 cost model is working as expected for the default ISA
+   (msp430x) and hwmult (none), when compiling at -O3.  */
+
+char arr[2];
+char a;
+char *ptr;
+
+/*
+** foo:
+** ...
+**	MOV.B	\&a, \&arr\+1
+**	MOV.*	#arr\+2, \&ptr
+** ...
+*/
+
+void
+foo (void)
+{
+  arr[1] = a;
+  ptr = arr + 2;
+}
+
+extern void ext (void);
+
+/*
+** bar:
+** ...
+**	CALL.*	#ext
+**	CALL.*	#ext
+** ...
+*/
+
+void
+bar (void)
+{
+  ext ();
+  ext ();
+}

gcc/testsuite/gcc.target/msp430/rtx-cost-O3-f5series.c

@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -mhwmult=f5series" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+/* Verify the MSP430 cost model is working as expected for the default ISA
+   (msp430x) and f5series hwmult, when compiling at -O3.  */
+
+volatile unsigned long a;
+volatile unsigned int b;
+volatile unsigned long c;
+unsigned long res1;
+unsigned long res2;
+unsigned long res3;
+
+/*
+** foo:
+** ...
+**	MOV.B	#16, R14
+**	CALL.*	#__mspabi_slll
+** ...
+**	MOV.*	\&res2.*
+** ...
+**	RLA.*RLC.*
+** ...
+**	MOV.*	\&res3.*
+** ...
+**	RLA.*RLC.*
+** ...
+*/
+void foo (void)
+{
+  /* Use the shift library function for this.  */
+  res1 = (a << 16) | b;
+  /* Emit 7 inline shifts for this.  */
+  res2 *= 128;
+  /* Perform this multiplication inline, using addition and shifts.  */
+  res3 *= 100;
+}

gcc/testsuite/gcc.target/msp430/rtx-cost-Os-default.c

@@ -0,0 +1,43 @@
+/* { dg-do compile } */
+/* { dg-options "-Os" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+/* Verify the MSP430 cost model is working as expected for the default ISA
+   (msp430x) and hwmult (none), when compiling at -Os.  */
+
+char arr[2];
+char a;
+char *ptr;
+
+/*
+** foo:
+** ...
+**	MOV.B	\&a, \&arr\+1
+**	MOV.*	#arr\+2, \&ptr
+** ...
+*/
+
+void
+foo (void)
+{
+  arr[1] = a;
+  ptr = arr + 2;
+}
+
+extern void ext (void);
+
+/*
+** bar:
+** ...
+**	MOV.*	#ext, R10
+**	CALL.*	R10
+**	CALL.*	R10
+** ...
+*/
+
+void
+bar (void)
+{
+  ext ();
+  ext ();
+}

gcc/testsuite/gcc.target/msp430/rtx-cost-Os-f5series.c

@@ -0,0 +1,38 @@
+/* { dg-do compile } */
+/* { dg-options "-Os -mhwmult=f5series" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+/* Verify the MSP430 cost model is working as expected for the default ISA
+   (msp430x) and f5series hwmult, when compiling at -Os.  */
+
+volatile unsigned long a;
+volatile unsigned int b;
+volatile unsigned long c;
+unsigned long res1;
+unsigned long res2;
+unsigned long res3;
+
+/*
+** foo:
+** ...
+**	MOV.B	#16, R14
+**	CALL.*	#__mspabi_slll
+** ...
+**	MOV.B	#7, R14
+**	CALL.*	#__mspabi_slll
+** ...
+**	MOV.B	#100, R14
+**	MOV.B	#0, R15
+** ...
+**	CALL.*	#__mulsi2_f5
+** ...
+*/
+void foo (void)
+{
+  /* Use the shift library function for this.  */
+  res1 = (a << 16) | b;
+  /* Likewise.  */
+  res2 *= 128;
+  /* Use the hardware multiply library function for this.  */
+  res3 *= 100;
+}