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author | Roman Lebedev <lebedev.ri@gmail.com> | 2018-06-06 19:38:16 +0000 |
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committer | Roman Lebedev <lebedev.ri@gmail.com> | 2018-06-06 19:38:16 +0000 |
commit | 488d28d4e5d083caf8353e6df726897bf23fa1ad (patch) | |
tree | f7acb6a1e0e297687cb994a13a8ec32a986e76d4 /lldb/packages/Python/lldbsuite/test/python_api/frame/main.c | |
parent | cb56f7a5502ca5029557e5f8a90c4a149021c33f (diff) | |
download | bcm5719-llvm-488d28d4e5d083caf8353e6df726897bf23fa1ad.tar.gz bcm5719-llvm-488d28d4e5d083caf8353e6df726897bf23fa1ad.zip |
[X86] Emit BZHI when mask is ~(-1 << nbits))
Summary:
In D47428, i propose to choose the `~(-(1 << nbits))` as the canonical form of low-bit-mask formation.
As it is seen from these tests, there is a reason for that.
AArch64 currently better handles `~(-(1 << nbits))`, but not the more traditional `(1 << nbits) - 1` (sic!).
The other way around for X86.
It would be much better to canonicalize.
This patch is completely monkey-typing.
I don't really understand how this works :)
I have based it on `// x & (-1 >> (32 - y))` pattern.
Also, when we only have `BMI`, i wonder if we could use `BEXTR` with `start=0` ?
Related links:
https://bugs.llvm.org/show_bug.cgi?id=36419
https://bugs.llvm.org/show_bug.cgi?id=37603
https://bugs.llvm.org/show_bug.cgi?id=37610
https://rise4fun.com/Alive/idM
Reviewers: craig.topper, spatel, RKSimon, javed.absar
Reviewed By: craig.topper
Subscribers: kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D47453
llvm-svn: 334125
Diffstat (limited to 'lldb/packages/Python/lldbsuite/test/python_api/frame/main.c')
0 files changed, 0 insertions, 0 deletions