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[arm] Correct cost calculations involving borrow for subtracts.

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The rtx_cost calculations when a borrow operation was being performed were
not being calculated correctly.  The borrow is free as part of the
subtract-with-carry instructions.  This patch recognizes the various
idioms that can describe this and returns the correct costs.

	* config/arm/arm.c (arm_rtx_costs_internal, case MINUS): Handle
	borrow operations.

From-SVN: r277173
This commit is contained in:
Richard Earnshaw 2019-10-18 19:02:50 +00:00 committed by Richard Earnshaw
parent 0a67306e3c
commit bbead5babc
2 changed files with 47 additions and 7 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2019-10-18 Richard Earnshaw <rearnsha@arm.com>
* config/arm/arm.c (arm_rtx_costs_internal, case MINUS): Handle
borrow operations.
2019-10-18 Richard Earnshaw <rearnsha@arm.com>
* config/arm/arm.c (strip_carry_operation): New function.

49
gcc/config/arm/arm.c
View File

@ -10049,15 +10049,46 @@ arm_rtx_costs_internal (rtx x, enum rtx_code code, enum rtx_code outer_code,
rtx shift_by_reg = NULL;
rtx shift_op;
rtx non_shift_op;
rtx op0 = XEXP (x, 0);
rtx op1 = XEXP (x, 1);
shift_op = shifter_op_p (XEXP (x, 0), &shift_by_reg);
/* Factor out any borrow operation. There's more than one way
of expressing this; try to recognize them all. */
if (GET_CODE (op0) == MINUS)
{
if (arm_borrow_operation (op1, SImode))
{
op1 = XEXP (op0, 1);
op0 = XEXP (op0, 0);
}
else if (arm_borrow_operation (XEXP (op0, 1), SImode))
op0 = XEXP (op0, 0);
}
else if (GET_CODE (op1) == PLUS
&& arm_borrow_operation (XEXP (op1, 0), SImode))
op1 = XEXP (op1, 0);
else if (GET_CODE (op0) == NEG
&& arm_borrow_operation (op1, SImode))
{
/* Negate with carry-in. For Thumb2 this is done with
SBC R, X, X lsl #1 (ie X - 2X - C) as Thumb lacks the
RSC instruction that exists in Arm mode. */
if (speed_p)
*cost += (TARGET_THUMB2
? extra_cost->alu.arith_shift
: extra_cost->alu.arith);
*cost += rtx_cost (XEXP (op0, 0), mode, MINUS, 0, speed_p);
return true;
}
shift_op = shifter_op_p (op0, &shift_by_reg);
if (shift_op == NULL)
{
shift_op = shifter_op_p (XEXP (x, 1), &shift_by_reg);
non_shift_op = XEXP (x, 0);
shift_op = shifter_op_p (op1, &shift_by_reg);
non_shift_op = op0;
}
else
non_shift_op = XEXP (x, 1);
non_shift_op = op1;
if (shift_op != NULL)
{
@ -10087,10 +10118,10 @@ arm_rtx_costs_internal (rtx x, enum rtx_code code, enum rtx_code outer_code,
return true;
}
if (CONST_INT_P (XEXP (x, 0)))
if (CONST_INT_P (op0))
{
int insns = arm_gen_constant (MINUS, SImode, NULL_RTX,
INTVAL (XEXP (x, 0)), NULL_RTX,
INTVAL (op0), NULL_RTX,
NULL_RTX, 1, 0);
*cost = COSTS_N_INSNS (insns);
if (speed_p)
@ -10101,7 +10132,11 @@ arm_rtx_costs_internal (rtx x, enum rtx_code code, enum rtx_code outer_code,
else if (speed_p)
*cost += extra_cost->alu.arith;
return false;
/* Don't recurse as we don't want to cost any borrow that
we've stripped. */
*cost += rtx_cost (op0, mode, MINUS, 0, speed_p);
*cost += rtx_cost (op1, mode, MINUS, 1, speed_p);
return true;
}
if (GET_MODE_CLASS (mode) == MODE_INT