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Update VarInfo's comments to reflect the current code. LiveVar
no longer records a unique defining instruction, and virtual registers may have multiple kills while still being defined and killed in the same block. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59145 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -47,20 +47,17 @@ public:
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/// VarInfo - This represents the regions where a virtual register is live in
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/// the program. We represent this with three different pieces of
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/// information: the instruction that uniquely defines the value, the set of
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/// blocks the instruction is live into and live out of, and the set of
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/// non-phi instructions that are the last users of the value.
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/// information: the set of blocks in which the instruction is live
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/// throughout, the set of blocks in which the instruction is actually used,
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/// and the set of non-phi instructions that are the last users of the value.
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///
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/// In the common case where a value is defined and killed in the same block,
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/// There is one killing instruction, and AliveBlocks is empty.
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///
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/// Otherwise, the value is live out of the block. If the value is live
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/// across any blocks, these blocks are listed in AliveBlocks. Blocks where
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/// the liveness range ends are not included in AliveBlocks, instead being
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/// captured by the Kills set. In these blocks, the value is live into the
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/// block (unless the value is defined and killed in the same block) and lives
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/// until the specified instruction. Note that there cannot ever be a value
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/// whose Kills set contains two instructions from the same basic block.
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/// If the value is live throughout any blocks, these blocks are listed in
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/// AliveBlocks. Blocks where the liveness range ends are not included in
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/// AliveBlocks, instead being captured by the Kills set. In these blocks,
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/// the value is live into the block (unless the value is defined and killed
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/// in the same block) and lives until the specified instruction. Note that
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/// there cannot ever be a value whose Kills set contains two instructions
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/// from the same basic block.
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///
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/// PHI nodes complicate things a bit. If a PHI node is the last user of a
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/// value in one of its predecessor blocks, it is not listed in the kills set,
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@ -72,13 +69,13 @@ public:
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/// included). This is sensical because the value must be live to the end of
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/// the block, but is not live in any successor blocks.
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struct VarInfo {
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/// AliveBlocks - Set of blocks of which this value is alive completely
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/// AliveBlocks - Set of blocks in which this value is alive completely
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/// through. This is a bit set which uses the basic block number as an
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/// index.
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///
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BitVector AliveBlocks;
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/// UsedBlocks - Set of blocks of which this value is actually used. This
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/// UsedBlocks - Set of blocks in which this value is actually used. This
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/// is a bit set which uses the basic block number as an index.
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BitVector UsedBlocks;
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