================
@@ -103,6 +103,13 @@ class TypeDescriptor {
/// representation is that of bitcasting the floating-point value to an
/// integer type.
TK_Float = 0x0001,
+ /// An _BitInt(N) type. Lowest bit is 1 for a signed value, 0 for an
+ /// unsigned value. Remaining bits are log_2(bit_width). The value
----------------
jakubjelinek wrote:
bit_width of what? The main problem is that the _BitInt ABI is only defined in
the x86-64 and aarch64 psABIs, for i686 the word was that the ABI should be
whatever GCC implemented, but nobody updated the ia32 psABI yet.
I think ARM 32-bit is defined too, some other targets are working on it.
As documented in LLVM, it implements _BitInt everywhere but notes that the ABI
can change (GCC took a different approach, only implementing it for arches
which agree on an ABI).
So, if compiler-rt implements _BitInt support, it better be able to encode the
various ABIs which will be used for _BitInt on various arches.
The current ABIs usually have some special cases for smaller number of bits,
but those generally can be encoded as normal integer (sign or zero extended say
to long long or __int128).
For the large _BitInts, x86_64 uses little endian ordered array of 64-bit
limbs, aarch64 little or big endian ordered array of 128-bit limbs, ia32 little
endian ordered array of 32-bit limbs.
But I was told the powerpc folks are considering little endian ordering of
limbs on both ppc64le and ppc64 big-endian.
So, I think you certainly want to encode the limb size and the N from
_BitInt(N) and whether it is signed or unsigned and possibly (e.g. for ppc64)
also whether the limbs are ordered from least significant to most or vice versa
(bit ordering within limb would be normally dependent on endianity).
So, I think that bit_width in the bits above sign should be the limb size, not
_BitInt size rounded up or whatever you're implementing right now. And encode
somewhere the endianity too.
https://github.com/llvm/llvm-project/pull/96240
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