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| author | James Molloy <james.molloy@arm.com> | 2016-01-14 15:23:19 +0000 |
|---|---|---|
| committer | James Molloy <james.molloy@arm.com> | 2016-01-14 15:23:19 +0000 |
| commit | a9497f53c93aa3ab575b108e8cc353941e785063 (patch) | |
| tree | 4bbf3b66b76972bc5f2d131970eed19db774f08d /llvm/lib/Transforms/Utils/Local.cpp | |
| parent | b28ae10a163e4be5ef4553987d6e0104b7f806bf (diff) | |
| download | llvm-a9497f53c93aa3ab575b108e8cc353941e785063.zip llvm-a9497f53c93aa3ab575b108e8cc353941e785063.tar.gz llvm-a9497f53c93aa3ab575b108e8cc353941e785063.tar.bz2 | |
[ValueTracking] Understand more select patterns in ComputeKnownBits
Some patterns of select+compare allow us to know exactly the value of the uppermost bits in the select result. For example:
%b = icmp ugt i32 %a, 5
%c = select i1 %b, i32 2, i32 %a
Here we know that %c is bounded by 5, and therefore KnownZero = ~APInt(5).getActiveBits() = ~7.
There are several such patterns, and this patch attempts to understand a reasonable subset of them - namely when the base values are the same (as above), and when they are related by a simple (add nsw), for example (add nsw %a, 4) and %a.
llvm-svn: 257769
Diffstat (limited to 'llvm/lib/Transforms/Utils/Local.cpp')
0 files changed, 0 insertions, 0 deletions