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LowerBitSets: Align referenced globals.

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This change aligns globals to the next highest power of 2 bytes, up to a
maximum of 128. This makes it more likely that we will be able to compress
bit sets with a greater alignment. In many more cases, we can now take
advantage of a new optimization also introduced in this patch that removes
bit set checks if the bit set is all ones.

The 128 byte maximum was found to provide the best tradeoff between instruction
overhead and data overhead in a recent build of Chromium. It allows us to
remove ~2.4MB of instructions at the cost of ~250KB of data.

Differential Revision: http://reviews.llvm.org/D7873

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230540 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Peter Collingbourne
2015-02-25 20:42:41 +00:00
parent 814efef67f
commit d63e5ad9c5
6 changed files with 101 additions and 73 deletions
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11
include/llvm/Transforms/IPO/LowerBitSets.h
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@@ -48,6 +48,17 @@ struct BitSetInfo {
return Bits.size() == 1 && Bits[0] == 1;
}
bool isAllOnes() const {
for (unsigned I = 0; I != Bits.size() - 1; ++I)
if (Bits[I] != 0xFF)
return false;
if (BitSize % 8 == 0)
return Bits[Bits.size() - 1] == 0xFF;
return Bits[Bits.size() - 1] == (1 << (BitSize % 8)) - 1;
}
bool containsGlobalOffset(uint64_t Offset) const;
bool containsValue(const DataLayout *DL,