The form that compares against 0 is better because:
1. It removes a use of the input value.
2. It's the more standard form for this pattern: https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
3. It results in equal or better codegen (tested with x86, AArch64, ARM, PowerPC, MIPS).
This is a root cause for PR42314, but probably doesn't completely answer the codegen request:
https://bugs.llvm.org/show_bug.cgi?id=42314
Alive proof:
https://rise4fun.com/Alive/9kG
Name: is power-of-2
%neg = sub i32 0, %x
%a = and i32 %neg, %x
%r = icmp eq i32 %a, %x
=>
%dec = add i32 %x, -1
%a2 = and i32 %dec, %x
%r = icmp eq i32 %a2, 0
Name: is not power-of-2
%neg = sub i32 0, %x
%a = and i32 %neg, %x
%r = icmp ne i32 %a, %x
=>
%dec = add i32 %x, -1
%a2 = and i32 %dec, %x
%r = icmp ne i32 %a2, 0
llvm-svn: 363956
Should also be marked writeonly, but I think that would require
splitting the version with done set to a separate intrinsic
Test change is only from renumbering the attribute group numbers,
which for some reason the generated check lines consider.
llvm-svn: 363560
Fix folds of addo and subo with an undef operand to be:
`@llvm.{u,s}{add,sub}.with.overflow` all fold to `{ undef, false }`,
as per LLVM undef rules.
Same for commuted variants.
Based on the original version of the patch by @nikic.
Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=42209 | PR42209 ]]
Differential Revision: https://reviews.llvm.org/D63065
llvm-svn: 363522
I'm not 100% sure about this, since I'm worried about IR transforms
that might end up introducing divergence downstream once replaced with
a constant, but I haven't come up with an example yet.
llvm-svn: 363406
Similar to rL362909:
This isn't the ideal fix (use FMF on the select), but it's still an
improvement until we have better FMF propagation to selects and other
FP math operators.
I don't think there's much risk of regression from this change by
not including the FMF on the fcmp any more. The nsz/nnan FMF
should be the same on the fcmp and the fsub because they have the
same operand.
llvm-svn: 362943
The `icmp sgt`/`icmp sle` variants are, too, miscompiles:
https://rise4fun.com/Alive/JFNPhttps://rise4fun.com/Alive/jHvL
A precondition 'x != 0' was forgotten by me.
While ensuring test coverage for `-1`, also add test coverage
for `0` mask. Mask `0` is allowed for all the folds,
mask `-1` is allowed for all the folds with unsigned `icmp` pred.
Constant mask `0` is missed though.
https://bugs.llvm.org/show_bug.cgi?id=42198
llvm-svn: 362910
This isn't the ideal fix (use FMF on the select), but it's still an
improvement until we have better FMF propagation to selects and other
FP math operators.
I don't think there's much risk of regression from this change by
not including the FMF on the fcmp any more. The nsz/nnan FMF
should be the same on the fcmp and the fneg (fsub) because they
have the same operand.
This works around the most glaring FMF logical inconsistency cited
in PR38086:
https://bugs.llvm.org/show_bug.cgi?id=38086
llvm-svn: 362909
When the byval attribute has a type, it must match the pointee type of
any parameter; but InstCombine was not updating the attribute when
folding casts of various kinds away.
llvm-svn: 362643
When the object size argument is -1, no checking can be done, so calling the
_chk variant is unnecessary. We already did this for a bunch of these
functions.
rdar://50797197
Differential revision: https://reviews.llvm.org/D62358
llvm-svn: 362272
It looks this fold was already partially happening, indirectly
via some other folds, but with one-use limitation.
No other fold here has that restriction.
https://rise4fun.com/Alive/ftR
llvm-svn: 362217
David Bolvansky