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(simplify_binary_operation, case PLUS, MINUS): 

Simplify such things as (X >> 1) - X.

From-SVN: r6308
This commit is contained in:
Richard Kenner 1993-12-24 21:24:39 -05:00
parent 6e7f952e96
commit 30d69925b6
1 changed files with 108 additions and 0 deletions
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108
gcc/cse.c
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@ -3477,6 +3477,60 @@ simplify_binary_operation (code, mode, op0, op1)
&& GET_CODE (op0) == CONST_INT)
return plus_constant (op1, INTVAL (op0));
/* See if this is something like X * C - X or vice versa or
if the multiplication is written as a shift. If so, we can
distribute and make a new multiply, shift, or maybe just
have X (if C is 2 in the example above). But don't make
real multiply if we didn't have one before. */
if (! FLOAT_MODE_P (mode))
{
HOST_WIDE_INT coeff0 = 1, coeff1 = 1;
rtx lhs = op0, rhs = op1;
int had_mult = 0;
if (GET_CODE (lhs) == NEG)
coeff0 = -1, lhs = XEXP (lhs, 0);
else if (GET_CODE (lhs) == MULT
&& GET_CODE (XEXP (lhs, 1)) == CONST_INT)
{
coeff0 = INTVAL (XEXP (lhs, 1)), lhs = XEXP (lhs, 0);
had_mult = 1;
}
else if (GET_CODE (lhs) == ASHIFT
&& GET_CODE (XEXP (lhs, 1)) == CONST_INT
&& INTVAL (XEXP (lhs, 1)) >= 0
&& INTVAL (XEXP (lhs, 1)) < HOST_BITS_PER_WIDE_INT)
{
coeff0 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (lhs, 1));
lhs = XEXP (lhs, 0);
}
if (GET_CODE (rhs) == NEG)
coeff1 = -1, rhs = XEXP (rhs, 0);
else if (GET_CODE (rhs) == MULT
&& GET_CODE (XEXP (rhs, 1)) == CONST_INT)
{
coeff1 = INTVAL (XEXP (rhs, 1)), rhs = XEXP (rhs, 0);
had_mult = 1;
}
else if (GET_CODE (rhs) == ASHIFT
&& GET_CODE (XEXP (rhs, 1)) == CONST_INT
&& INTVAL (XEXP (rhs, 1)) >= 0
&& INTVAL (XEXP (rhs, 1)) < HOST_BITS_PER_WIDE_INT)
{
coeff1 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (rhs, 1));
rhs = XEXP (rhs, 0);
}
if (rtx_equal_p (lhs, rhs))
{
tem = cse_gen_binary (MULT, mode, lhs,
GEN_INT (coeff0 + coeff1));
return (GET_CODE (tem) == MULT && ! had_mult) ? 0 : tem;
}
}
/* If one of the operands is a PLUS or a MINUS, see if we can
simplify this by the associative law.
Don't use the associative law for floating point.
@ -3532,6 +3586,60 @@ simplify_binary_operation (code, mode, op0, op1)
if (op1 == CONST0_RTX (mode))
return op0;
/* See if this is something like X * C - X or vice versa or
if the multiplication is written as a shift. If so, we can
distribute and make a new multiply, shift, or maybe just
have X (if C is 2 in the example above). But don't make
real multiply if we didn't have one before. */
if (! FLOAT_MODE_P (mode))
{
HOST_WIDE_INT coeff0 = 1, coeff1 = 1;
rtx lhs = op0, rhs = op1;
int had_mult = 0;
if (GET_CODE (lhs) == NEG)
coeff0 = -1, lhs = XEXP (lhs, 0);
else if (GET_CODE (lhs) == MULT
&& GET_CODE (XEXP (lhs, 1)) == CONST_INT)
{
coeff0 = INTVAL (XEXP (lhs, 1)), lhs = XEXP (lhs, 0);
had_mult = 1;
}
else if (GET_CODE (lhs) == ASHIFT
&& GET_CODE (XEXP (lhs, 1)) == CONST_INT
&& INTVAL (XEXP (lhs, 1)) >= 0
&& INTVAL (XEXP (lhs, 1)) < HOST_BITS_PER_WIDE_INT)
{
coeff0 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (lhs, 1));
lhs = XEXP (lhs, 0);
}
if (GET_CODE (rhs) == NEG)
coeff1 = - 1, rhs = XEXP (rhs, 0);
else if (GET_CODE (rhs) == MULT
&& GET_CODE (XEXP (rhs, 1)) == CONST_INT)
{
coeff1 = INTVAL (XEXP (rhs, 1)), rhs = XEXP (rhs, 0);
had_mult = 1;
}
else if (GET_CODE (rhs) == ASHIFT
&& GET_CODE (XEXP (rhs, 1)) == CONST_INT
&& INTVAL (XEXP (rhs, 1)) >= 0
&& INTVAL (XEXP (rhs, 1)) < HOST_BITS_PER_WIDE_INT)
{
coeff1 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (rhs, 1));
rhs = XEXP (rhs, 0);
}
if (rtx_equal_p (lhs, rhs))
{
tem = cse_gen_binary (MULT, mode, lhs,
GEN_INT (coeff0 - coeff1));
return (GET_CODE (tem) == MULT && ! had_mult) ? 0 : tem;
}
}
/* (a - (-b)) -> (a + b). */
if (GET_CODE (op1) == NEG)
return cse_gen_binary (PLUS, mode, op0, XEXP (op1, 0));