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b19a7319a9
LCSSA from it caused a crasher with the LoopUnroll pass. This crasher is really nasty. We destroy LCSSA form in a suprising way. When unrolling a loop into an outer loop, we not only need to restore LCSSA form for the outer loop, but for all children of the outer loop. This is somewhat obvious in retrospect, but hey! While this seems pretty heavy-handed, it's not that bad. Fundamentally, we only do this when we unroll a loop, which is already a heavyweight operation. We're unrolling all of these hypothetical inner loops as well, so their size and complexity is already on the critical path. This is just adding another pass over them to re-canonicalize. I have a test case from PR18616 that is great for reproducing this, but pretty useless to check in as it relies on many 10s of nested empty loops that get unrolled and deleted in just the right order. =/ What's worse is that investigating this has exposed another source of failure that is likely to be even harder to test. I'll try to come up with test cases for these fixes, but I want to get the fixes into the tree first as they're causing crashes in the wild. llvm-svn: 200273
64 lines
2.0 KiB
C++
64 lines
2.0 KiB
C++
//===- llvm/Transforms/Utils/LoopUtils.h - Loop utilities -*- C++ -*-=========//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines some loop transformation utilities.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_UTILS_LOOPUTILS_H
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#define LLVM_TRANSFORMS_UTILS_LOOPUTILS_H
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namespace llvm {
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class AliasAnalysis;
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class BasicBlock;
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class DominatorTree;
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class Loop;
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class LoopInfo;
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class Pass;
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class ScalarEvolution;
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BasicBlock *InsertPreheaderForLoop(Loop *L, Pass *P);
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/// \brief Simplify each loop in a loop nest recursively.
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///
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/// This takes a potentially un-simplified loop L (and its children) and turns
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/// it into a simplified loop nest with preheaders and single backedges. It
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/// will optionally update \c AliasAnalysis and \c ScalarEvolution analyses if
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/// passed into it.
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bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
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AliasAnalysis *AA = 0, ScalarEvolution *SE = 0);
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/// \brief Put loop into LCSSA form.
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///
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/// Looks at all instructions in the loop which have uses outside of the
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/// current loop. For each, an LCSSA PHI node is inserted and the uses outside
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/// the loop are rewritten to use this node.
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///
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/// LoopInfo and DominatorTree are required and preserved.
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///
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/// If ScalarEvolution is passed in, it will be preserved.
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///
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/// Returns true if any modifications are made to the loop.
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bool formLCSSA(Loop &L, DominatorTree &DT, ScalarEvolution *SE = 0);
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/// \brief Put a loop nest into LCSSA form.
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///
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/// This recursively forms LCSSA for a loop nest.
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///
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/// LoopInfo and DominatorTree are required and preserved.
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///
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/// If ScalarEvolution is passed in, it will be preserved.
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///
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/// Returns true if any modifications are made to the loop.
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bool formLCSSARecursively(Loop &L, DominatorTree &DT, ScalarEvolution *SE = 0);
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}
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#endif
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