thakis closed this revision.
thakis added a comment.
r337619, thanks! The hoisting point is a good one; will rewrite using
funnelshift once that's possible :-)
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spatel added a comment.
In https://reviews.llvm.org/D49606#1170448, @thakis wrote:
> Isn't implementing this in plain old C the nicest approach anyhow, even once
> funnel shift exists?
No, the primary reason for creating the intrinsic is that we can’t guarantee
that we’ll recognize the
craig.topper accepted this revision.
craig.topper added a comment.
This revision is now accepted and ready to land.
LGTM. I'm inclined to let this go in now since we have a requested use for it.
We can change it to funnel shift once we're confident in the backend.
craig.topper added a comment.
The only weird thing that I can really think of with the C version is that the
'and' on the shift amount might get hoisted out of a loop and not get dropped
during isel.
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thakis added a comment.
Isn't implementing this in plain old C the nicest approach anyhow, even once
funnel shift exists?
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craig.topper added a comment.
@spatel, yes its exactly funnel shift. I wasn't sure if we were ready for clang
to create it yet or not. Can we let this go as is and change it to funnel shift
once we have the variable case fixed in the backend?
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thakis added a comment.
Now with C builtins which get nicely optimized.
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thakis updated this revision to Diff 156596.
thakis edited the summary of this revision.
https://reviews.llvm.org/D49606
Files:
clang/lib/Headers/intrin.h
clang/test/Headers/ms-intrin.cpp
Index: clang/test/Headers/ms-intrin.cpp
spatel added a comment.
In https://reviews.llvm.org/D49606#1170278, @craig.topper wrote:
> Here are the IR patterns for this that work. Not sure if we can do this
> directly in C, we need a 128 bit type, but maybe we can emit it from
> CGBuiltin.cpp?
>
> define i64 @__shiftleft128(i64 %x,
craig.topper added a comment.
I'd prefer the pattern over inline assembly. It'll give us more flexibility in
the backend if we should be using some other instruction on different targets.
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thakis added a comment.
We have __int128. If you think hitting the pattern is preferable to inline asm,
I can try to give that a try, either via C or via CGBuiltin.cpp.
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craig.topper added a comment.
Here are the IR patterns for this that work. Not sure if we can do this
directly in C, we need a 128 bit type, but maybe we can emit it from
CGBuiltin.cpp?
define i64 @__shiftleft128(i64 %x, i64 %y, i8 %amt) {
%a = zext i64 %x to i128
%b = zext i64 %y to
craig.topper added a comment.
@spatel, should this ultimately use funnel shift?
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thakis created this revision.
thakis added a reviewer: craig.topper.
cl.exe maps these to shld / shrd, so let's do the same. ISel has
`Subtarget->isSHLDSlow()` to prevent use of these intrinsics on some machines,
but honoring them feels a bit like trying to outsmart the intrinsics user, and
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