george.burgess.iv added a comment.
> Does this have any significant impact on -fsyntax-only performance?
I'm sure there are pathological cases where this hurts perf, but my intuition
tells me that we won't get bitten badly by any of them in the real world. It
should be a branch per cast + full expr for people who don't use it. For those
who do, we're walking 2 types for each cast (plus maybe constexpr evaluations
for casts from FP/vec to non-FP/vec values), and walking the types for each
FullExpr.
Again, you can likely craft code that makes this expensive (which we can likely
fix with strategically-placed caches), but being bitten by that in practice
seems somewhat unlikely to me. Happy to try and add caching and/or take numbers
with caches if you'd like.
To evaluate the build time impact of this, I did 20 builds of aarch64 Linux
with/without this patch. Of the metrics I tracked (memory, system/user/wall
time), all reported differences were < their stdev except for user time. User
time regression with this patch was 0.37%, with a stdev of 0.12%. Happy to try
to gather -fsyntax-only numbers if there's a simple way to do that.
================
Comment at: clang/lib/Driver/ToolChains/Arch/AArch64.cpp:194
Features.push_back("-crypto");
Features.push_back("-neon");
+ // FIXME: Ideally, we'd also like to pass a `+general-regs-only` feature,
----------------
efriedma wrote:
> Do we need to get rid of the "-neon" etc.?
Yeah, good call. Looks like I forgot a "RUN:" in my tests checking for whether
or not asm works, so the thing that should've caught that wasn't enabled. :)
================
Comment at: clang/lib/Sema/SemaExprCXX.cpp:7997
+ bool isRValueOfIllegalType(const Expr *E) const {
+ return E->getValueKind() != VK_LValue && !isGeneralType(E);
+ }
----------------
efriedma wrote:
> Should this be `E->isRValue()`? Not that the difference really matters for
> C, but it affects rvalue references in C++.
Yeah, flipped to that and added tests -- thanks
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D38479/new/
https://reviews.llvm.org/D38479
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