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path: root/llvm/lib/CodeGen/SpillPlacement.cpp
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* Give a small negative bias to giant edge bundles.Jakob Stoklund Olesen2012-05-211-0/+11
| | | | | | | | | | | | | | | | This helps compile time when the greedy register allocator splits live ranges in giant functions. Without the bias, we would try to grow regions through the giant edge bundles, usually to find out that the region became too big and expensive. If a live range has many uses in blocks near the giant bundle, the small negative bias doesn't make a big difference, and we still consider regions including the giant edge bundle. Giant edge bundles are usually connected to landing pads or indirect branches. llvm-svn: 157174
* Be more conservative when forming compact regions.Jakob Stoklund Olesen2011-08-031-1/+3
| | | | | | | | | | | | | | | Apply twice the negative bias on transparent blocks when computing the compact regions. This excludes loop backedges from the region when only one of the loop blocks uses the register. Previously, we would include the backedge in the region if the loop preheader and the loop latch both used the register, but the loop header didn't. When both the header and latch blocks use the register, we still keep it live on the backedge. llvm-svn: 136832
* Extend the SpillPlacement interface with two new features.Jakob Stoklund Olesen2011-08-021-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | The PrefBoth constraint is used for blocks that ideally want a live-in value both on the stack and in a register. This would be used by a block that has a use before interference forces a spill. Secondly, add the ChangesValue flag to BlockConstraint. This tells SpillPlacement if a live-in value on the stack can be reused as a live-out stack value for free. If the block redefines the virtual register, a spill would be required for that. This extra information will be used by SpillPlacement to more accurately calculate spill costs when a value can exist both on the stack and in a register. The simplest example is a basic block that reads the virtual register, but doesn't change its value. Spilling around such a block requires a reload, but no spill in the block. The spiller already knows this, but the spill placer doesn't. That can sometimes lead to suboptimal regions. llvm-svn: 136731
* Add a simple method for marking blocks with interference in and out.Jakob Stoklund Olesen2011-07-231-0/+14
| | | | | | | | | | This method matches addLinks - All the listed blocks are considered to have interference, so they add a negative bias to their bundles. This could also be done by addConstraints, but that requires building a separate BlockConstraint array. llvm-svn: 135844
* Build the Hopfield network incrementally when splitting global live ranges.Jakob Stoklund Olesen2011-04-091-27/+44
| | | | | | | | | It is common for large live ranges to have few basic blocks with register uses and many live-through blocks without any uses. This approach grows the Hopfield network incrementally around the use blocks, completely avoiding checking interference for some through blocks. llvm-svn: 129188
* Prefer multiplications to divisions.Jakob Stoklund Olesen2011-04-071-7/+13
| | | | llvm-svn: 129080
* Extract SpillPlacement::addLinks for handling the special transparent blocks.Jakob Stoklund Olesen2011-04-071-17/+18
| | | | llvm-svn: 129079
* Keep track of the number of positively biased nodes when adding constraints.Jakob Stoklund Olesen2011-04-061-3/+8
| | | | | | If there are no positive nodes, the algorithm can be aborted early. llvm-svn: 129021
* Break the spill placement algorithm into three parts: prepare, ↵Jakob Stoklund Olesen2011-04-061-14/+13
| | | | | | | | addConstraints, and finish. This will allow us to abort the algorithm early if it is determined to be futile. llvm-svn: 129020
* Precompute block frequencies, pow() isn't free.Jakob Stoklund Olesen2011-03-041-11/+5
| | | | llvm-svn: 126975
* Trim debugging output.Jakob Stoklund Olesen2011-02-181-25/+0
| | | | llvm-svn: 125802
* Silence an MSVC warningJakob Stoklund Olesen2011-02-031-1/+1
| | | | llvm-svn: 124798
* Divert Hopfield network debug output. It is very noisy.Jakob Stoklund Olesen2011-01-191-1/+1
| | | | llvm-svn: 123859
* Add RAGreedy methods for splitting live ranges around regions.Jakob Stoklund Olesen2011-01-181-0/+1
| | | | | | | | | | Analyze the live range's behavior entering and leaving basic blocks. Compute an interference pattern for each allocation candidate, and use SpillPlacement to find an optimal region where that register can be live. This code is still not enabled. llvm-svn: 123774
* Add the SpillPlacement analysis pass.Jakob Stoklund Olesen2011-01-061-0/+354
This pass precomputes CFG block frequency information that can be used by the register allocator to find optimal spill code placement. Given an interference pattern, placeSpills() will compute which basic blocks should have the current variable enter or exit in a register, and which blocks prefer the stack. The algorithm is ready to consume block frequencies from profiling data, but for now it gets by with the static estimates used for spill weights. This is a work in progress and still not hooked up to RegAllocGreedy. llvm-svn: 122938
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