Self

The following is a list of simplifications done by the tree folder and the rtl simplifier (note this is not the C expressions but the tree/rtl based ones). Combine transforms marked as n/a are because combine_simplify_rtx calls simplify_binary_operation and friends.

Simplification

Tree Folder
(fold-const.c)

RTL Simplifier
(simplify-rtx.c)

Combine
(combine.c)

 i - C > i   -> false

yes in fold_binary (PR20922)

yes

n/a

 - (NOT A) -> A + 1

yes in fold_unary

yes in simplify_unary_operation_1

n/a

- (A + 1) -> NOT A

yes in fold_unary

yes in simplify_unary_operation_1

n/a

- (X - Y) -> Y - X

yes in negate_expr

yes in simplify_unary_operation_1

n/a

NOT (-A) -> A - 1

yes in fold_unary

yes in simplify_unary_operation_1 as A + -1.

n/a

NOT (NOT A) -> A

yes in fold_unary

yes in simplify_unary_operation_1

n/a

NOT (A - 1) -> -A

yes in fold_unary

yes in simplify_unary_operation_1

ABS (ABS X) -> ABS X

yes in fold_unary since ABS is nonnegative

no

yes in combine_simplify_rtx

ABS (-x) -> ABS X

yes in fold_unary

no

yes in combine_simplify_rtx

ABS X >= 0 -> true

yes in fold_binary

yes in simplify_const_relational_operation

n/a

ABS X < 0 -> false

yes in fold_binary

yes in simplify_const_relational_operation

n/a

x +/- 0 -> x

yes in fold_binary

yes in simplify_binary_operation_1

n/a

MIN (X, X) -> X

yes in fold_binary

yes in simplify_binary_operation_1

n/a

MAX (X, X) -> X

yes in fold_binary

yes in simplify_binary_operation_1

n/a

X % +/- 1 -> 0

yes in fold_binary

yes in simplify_binary_operation_1

n/a

0 % X -> 0

yes in fold_binary

yes in simplify_binary_operation_1

n/a

X & -1 -> X

yes in fold_binary

yes by X & NOT constant_with_bits_off_in_X in simplify_binary_operation_1

n/a

X & 0 -> 0

yes in fold_binary

yes in simplify_binary_operation_1

n/a

X & X -> X

yes in fold_binary

yes in simplify_binary_operation_1

n/a

NOT X & X -> 0

yes in fold_binary

yes in simplify_binary_operation_1

n/a

X & NOT X -> 0

yes in fold_binary

yes in simplify_binary_operation_1

n/a

NOT X & NOT Y -> NOT (X IOR Y)

yes in fold_binary

no

no

(NOT X) XOR (NOT Y) -> (X XOR Y)

yes in fold_binary

no

yes in simplify_logical

NOT (X XOR Y) -> (NOT X) XOR Y
or X XOR (NOT Y)

yes in fold_binary (To NOT (X XOR Y) is not done.)

no

yes in simplify_logical as (NOT X) XOR Y or X XOR (NOT Y) to NOT (X XOR Y)

((int)b & 1) != 0 -> (b & 1) != 0

PR14792

yes in simplify_relational_operation_1

n/a

(a >> c1)>>c2 -> a >> (c1 + c2)

yes in fold_binary, PR14796

yes

n/a

(a >> c) << c -> a & (-1 << c)

yes in fold_binary

?

?

(a << c) >> c -> a & (-1 >> c)
for unsigned a

yes in fold_binary

?

?

(int)(a+b) -> (int)a + (int)b

PR14844, is done also in the C/C++ front-ends

kinda, done after reload

no

a & b & ~a & ~b -> 0

PR15878

no

yes, re-associative

*&a->b -> a->b

PR17141

yes by expand, CSE, and others

n/a

x * -1 -> -x

yes in fold_binary

yes

n/a

&a["b"] - &a["c"] -> (b - c)*sizeof(*a)

yes in fold_binary PR21082

n/a

yes but because we expand it to be &a + b*sizeof(*a) - (&a + c*sizeof(*a))

(X >> C) & 1 != 0 -> X & C' != 0

PR21137

n/a

n/a

bool_var != 0 -> bool_var

yes in fold_binary PR15618

no and cannot be done, unless in BImode

n/a

A % (2**N) -> A & (2**N - 1)
for positive values of A

yes, in fold_binary

?

?

~X CMP ~Y -> Y CMP X

yes, in fold_comparison

?

?

x & ((~x) | y) -> y & x

NO PR33512

NO PR33512

n/a

None: Simplifications (last edited 2010-06-02 16:03:13 by PaoloBonzini)