+ /// VarInfo - This represents the regions where a virtual register is live in
+ /// the program. We represent this with three different pieces of
+ /// information: the set of blocks in which the instruction is live
+ /// throughout, the set of blocks in which the instruction is actually used,
+ /// and the set of non-phi instructions that are the last users of the value.
+ ///
+ /// In the common case where a value is defined and killed in the same block,
+ /// There is one killing instruction, and AliveBlocks is empty.
+ ///
+ /// Otherwise, the value is live out of the block. If the value is live
+ /// throughout any blocks, these blocks are listed in AliveBlocks. Blocks
+ /// where the liveness range ends are not included in AliveBlocks, instead
+ /// being captured by the Kills set. In these blocks, the value is live into
+ /// the block (unless the value is defined and killed in the same block) and
+ /// lives until the specified instruction. Note that there cannot ever be a
+ /// value whose Kills set contains two instructions from the same basic block.
+ ///
+ /// PHI nodes complicate things a bit. If a PHI node is the last user of a
+ /// value in one of its predecessor blocks, it is not listed in the kills set,
+ /// but does include the predecessor block in the AliveBlocks set (unless that
+ /// block also defines the value). This leads to the (perfectly sensical)
+ /// situation where a value is defined in a block, and the last use is a phi
+ /// node in the successor. In this case, AliveBlocks is empty (the value is
+ /// not live across any blocks) and Kills is empty (phi nodes are not
+ /// included). This is sensical because the value must be live to the end of
+ /// the block, but is not live in any successor blocks.
+ struct VarInfo {
+ /// AliveBlocks - Set of blocks in which this value is alive completely