Expand description
index dialect.
The Index dialect contains operations for manipulating values of the builtin
index type. The index type models target-specific values of pointer width,
like intptr_t. Index values are typically used as loop bounds, array
subscripts, tensor dimensions, etc.
The operations in this dialect operate exclusively on scalar index types. The dialect and its operations treat the index type as signless and contains signed and unsigned versions of certain operations where the distinction is meaningful. In particular, the operations and transformations are careful to be aware of the target-independent-ness of the index type, such as when folding.
The folding semantics of the Index dialect operations ensure that folding
produces the same results irrespective of the eventual target pointer width.
All index constants are stored in APInts of maximum index bitwidth: 64.
Operations are folded using 64-bit integer arithmetic.
For operations where the values of the upper 32 bits don’t impact the values of the lower 32 bits, no additional handling is required because if the target is 32-bit, the truncated folded result will be the same as if the operation were computed with 32-bit arithmetic, and if the target is 64-bit, the fold result is valid by default.
Consider addition: an overflow in 32-bit is the same as truncating the
result computed in 64-bit. For example, add(0x800000008, 0x800000008) is
0x1000000010 in 64-bit, which truncates to 0x10, the same result as
truncating the operands first: add(0x08, 0x08). Specifically, an operation
f can always be folded if it satisfies the following for all 64-bit values
of a and b:
trunc(f(a, b)) = f(trunc(a), trunc(b))
When materializing target-specific code, constants just need to be truncated as appropriate.
Operations where the values of the upper 32 bits do impact the values of the
lower 32 bits are not folded if the results would be different in 32-bit.
These are operations that right shift – division, remainder, etc. These
operations are only folded for subsets of a and b for which the above
property is satisfied. This is checked per fold attempt.
Consider division: the 32-bit computation will differ from 64-bit if the
latter results in a high bit shifted into the lower 32 bits. For example,
div(0x100000002, 2) is 0x80000001 in 64-bit but 0x01 in 32-bit; it
cannot be folded. However, div(0x200000002, 2) can be folded. The 64-bit
result is 0x100000001, which truncated to 32 bits is 0x01. The 32-bit
result of the operation with truncated operands div(0x02, 2) which is
0x01, the same as truncating the 64-bit result.
Structs§
- An
addoperation. Index addition. - A builder for an
addoperation. - An
andoperation. Index bitwise and. - A builder for an
andoperation. - A
bool.constantoperation. Boolean constant. - A builder for a
bool.constantoperation. - A
castsoperation. Index signed cast. - A builder for a
castsoperation. - A
castuoperation. Index unsigned cast. - A builder for a
castuoperation. - A
ceildivsoperation. Index signed ceil division. - A builder for a
ceildivsoperation. - A
ceildivuoperation. Index unsigned ceil division. - A builder for a
ceildivuoperation. - A
cmpoperation. Index compare. - A builder for a
cmpoperation. - A
constantoperation. Index constant. - A builder for a
constantoperation. - A
divsoperation. Index signed division. - A builder for a
divsoperation. - A
divuoperation. Index unsigned division. - A builder for a
divuoperation. - A
floordivsoperation. Index signed floor division. - A builder for a
floordivsoperation. - A
maxsoperation. Index signed maximum. - A builder for a
maxsoperation. - A
maxuoperation. Index unsigned maximum. - A builder for a
maxuoperation. - A
minsoperation. Index signed minimum. - A builder for a
minsoperation. - A
minuoperation. Index unsigned minimum. - A builder for a
minuoperation. - A
muloperation. Index multiplication. - A builder for a
muloperation. - An
oroperation. Index bitwise or. - A builder for an
oroperation. - A
remsoperation. Index signed remainder. - A builder for a
remsoperation. - A
remuoperation. Index unsigned remainder. - A builder for a
remuoperation. - A
shloperation. Index shift left. - A builder for a
shloperation. - A
shrsoperation. Signed index shift right. - A builder for a
shrsoperation. - A
shruoperation. Unsigned index shift right. - A builder for a
shruoperation. - A
sizeofoperation. Size in bits of the index type. - A builder for a
sizeofoperation. - A
suboperation. Index subtraction. - A builder for a
suboperation. - A
xoroperation. Index bitwise xor. - A builder for a
xoroperation.
Functions§
- Creates an
addoperation. - Creates an
andoperation. - Creates a
bool.constantoperation. - Creates a
castsoperation. - Creates a
castuoperation. - Creates a
ceildivsoperation. - Creates a
ceildivuoperation. - Creates a
cmpoperation. - Creates a
constantoperation. - Creates a
divsoperation. - Creates a
divuoperation. - Creates a
floordivsoperation. - Creates a
maxsoperation. - Creates a
maxuoperation. - Creates a
minsoperation. - Creates a
minuoperation. - Creates a
muloperation. - Creates an
oroperation. - Creates a
remsoperation. - Creates a
remuoperation. - Creates a
shloperation. - Creates a
shrsoperation. - Creates a
shruoperation. - Creates a
sizeofoperation. - Creates a
suboperation. - Creates a
xoroperation.