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| author | Matthias Braun <matthiasb@fb.com> | 2021-09-27 17:57:22 -0700 |
|---|---|---|
| committer | Matthias Braun <matthiasb@fb.com> | 2021-10-28 10:33:56 -0700 |
| commit | e2c7ee0743592e39274e28dbe0d0c213ba342317 (patch) | |
| tree | fdd0059b62ab09fe7a1480a16ceac32a2fc6bdd8 /llvm/lib/CodeGen/TwoAddressInstructionPass.cpp | |
| parent | 97a1570d8c31dc3bff12dd77b1ee824e1872bb69 (diff) | |
| download | llvm-e2c7ee0743592e39274e28dbe0d0c213ba342317.zip llvm-e2c7ee0743592e39274e28dbe0d0c213ba342317.tar.gz llvm-e2c7ee0743592e39274e28dbe0d0c213ba342317.tar.bz2 | |
X86InstrInfo: Support immediates that are +1/-1 different in optimizeCompareInstr
This extends `optimizeCompareInstr` to re-use previous comparison
results if the previous comparison was with an immediate that was 1
bigger or smaller. Example:
CMP x, 13
...
CMP x, 12 ; can be removed if we change the SETg
SETg ... ; x > 12 changed to `SETge` (x >= 13) removing CMP
Motivation: This often happens because SelectionDAG canonicalization
tends to add/subtract 1 often when optimizing for fallthrough blocks.
Example for `x > C` the fallthrough optimization switches true/false
blocks with `!(x > C)` --> `x <= C` and canonicalization turns this into
`x < C + 1`.
Differential Revision: https://reviews.llvm.org/D110867
Diffstat (limited to 'llvm/lib/CodeGen/TwoAddressInstructionPass.cpp')
0 files changed, 0 insertions, 0 deletions