Clang implemented the _ExtInt datatype as a bit-precise integer type,
which was then proposed to WG14. WG14 has accepted the proposal
(http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2709.pdf), but Clang
requires some additional work as a result.
In the original Clang implementation, we elected to disallow implicit
conversions involving these types until after WG14 finalized the rules.
This patch implements the rules decided by WG14: no integer promotion
for bit-precise types, conversions prefer the larger of the two types
and in the event of a tie (say _ExtInt(32) and a 32-bit int), the
standard type wins.
There are more changes still needed to conform to N2709, but those will
be handled in follow-up patches.
We're (temporarily) disabling ExtInt for the '__atomic' builtins so we can better design their behavior later. The idea is until we do an audit/design for the way atomic builtins are supposed to work with _ExtInt, we should leave them restricted so they don't limit our future options, such as by binding us to a sub-optimal implementation via ABI.
Example after this change:
$ cat test.c
void f(_ExtInt(64) *ptr) {
__atomic_fetch_add(ptr, 1, 0);
}
$ clang -c test.c
test.c:2:22: error: argument to atomic builtin of type '_ExtInt' is not supported
__atomic_fetch_add(ptr, 1, 0);
^
1 error generated.
Differential Revision: https://reviews.llvm.org/D84049
As reported in PR46774, an invalid arithemetic conversion used in a C
ternary operator resulted in an assertion. This patch replaces that
assertion with a diagnostic stating that the conversion failed.
At the moment, I believe the only case of this happening is _ExtInt
types.
My test needs a requires target clause to support inline assembly. This
patch splits out the asm tests into a separate test so we don't skip the
rest of the conditions.
The backends don't seem to properly handle the _ExtInt type in inline
assembly with crashes occurring in many. While the ones I tested seem to
work for powers of 2 < 64 (and some any multiple of 64 greater than
that), it seemed like a better idea to just use of this type in inline
assembly prohibited.
I added a limit to make sure that _ExtInt isn't exposed on systems that
haven't considered it in their ABI. The ext-int.cpp Sema test didn't
have a triple, so on non x86/x86_64 it would fail with this new error.
This patch adds said triple to make sure this passes.
This reverts commit 61ba1481e2.
I'm reverting this because it breaks the lldb build with
incomplete switch coverage warnings. I would fix it forward,
but am not familiar enough with lldb to determine the correct
fix.
lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:3958:11: error: enumeration values 'DependentExtInt' and 'ExtInt' not handled in switch [-Werror,-Wswitch]
switch (qual_type->getTypeClass()) {
^
lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:4633:11: error: enumeration values 'DependentExtInt' and 'ExtInt' not handled in switch [-Werror,-Wswitch]
switch (qual_type->getTypeClass()) {
^
lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp:4889:11: error: enumeration values 'DependentExtInt' and 'ExtInt' not handled in switch [-Werror,-Wswitch]
switch (qual_type->getTypeClass()) {
Introduction/Motivation:
LLVM-IR supports integers of non-power-of-2 bitwidth, in the iN syntax.
Integers of non-power-of-two aren't particularly interesting or useful
on most hardware, so much so that no language in Clang has been
motivated to expose it before.
However, in the case of FPGA hardware normal integer types where the
full bitwidth isn't used, is extremely wasteful and has severe
performance/space concerns. Because of this, Intel has introduced this
functionality in the High Level Synthesis compiler[0]
under the name "Arbitrary Precision Integer" (ap_int for short). This
has been extremely useful and effective for our users, permitting them
to optimize their storage and operation space on an architecture where
both can be extremely expensive.
We are proposing upstreaming a more palatable version of this to the
community, in the form of this proposal and accompanying patch. We are
proposing the syntax _ExtInt(N). We intend to propose this to the WG14
committee[1], and the underscore-capital seems like the active direction
for a WG14 paper's acceptance. An alternative that Richard Smith
suggested on the initial review was __int(N), however we believe that
is much less acceptable by WG14. We considered _Int, however _Int is
used as an identifier in libstdc++ and there is no good way to fall
back to an identifier (since _Int(5) is indistinguishable from an
unnamed initializer of a template type named _Int).
[0]https://www.intel.com/content/www/us/en/software/programmable/quartus-prime/hls-compiler.html)
[1]http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2472.pdf
Differential Revision: https://reviews.llvm.org/D73967
Aaron Ballman