llvm-6502

mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-10-07 05:55:44 +00:00

History

Shuxin Yang 5e915e6e36 Fix a SCEV update problem. The symptom is seg-fault, and the root cause is that a SCEV contains a SCEVUnknown which has null-pointer to a llvm::Value. This is how the problem take place: =================================== 1). In the pristine input IR, there are two relevant instrutions Op1 and Op2, Op1's corresponding SCEV (denoted as SCEV(op1)) is a SCEVUnknown, and SCEV(Op2) contains SCEV(Op1). None of these instructions are dead. Op1 : V1 = ... ... Op2 : V2 = ... // directly or indirectly (data-flow) depends on Op1 2) Optimizer (LSR in my case) generates an instruction holding the equivalent value of Op1, making Op1 dead. Op1': V1' = ... Op1: V1 = ... ; now dead) Op2 : V2 = ... //Now deps on Op1', but the SCEV(Op2) still contains SCEV(Op1) 3) Op1 is deleted, and call-back function is called to reset SCEV(Op1) to indicate it is invalid. However, SCEV(Op2) is not invalidated as well. 4) Following pass get the cached, invalid SCEV(Op2), and try to manipulate it, and cause segfault. The fix: ======== It seems there is no clean yet inexpensive fix. I write to dev-list soliciting good solution, unforunately no ack. So, I decide to fix this problem in a brute-force way: When ScalarEvolution::getSCEV is called, check if the cached SCEV contains a invalid SCEVUnknow, if yes, remove the cached SCEV, and re-evaluate the SCEV from scratch. I compile buch of big .c and .cpp, fortunately, I don't see any increase in compile time. Misc: ===== The reduced test-case has 2357 lines of code+other-stuff, too big to commit. rdar://14283433 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185843 91177308-0d34-0410-b5e6-96231b3b80d8		2013-07-08 17:33:13 +00:00
..
IPA	This patch breaks up Wrap.h so that it does not have to include all of	2013-05-01 20:59:00 +00:00
AliasAnalysis.cpp	Eliminate trivial redundant loads across nocapture+readonly calls to uncaptured	2013-07-07 10:15:16 +00:00
AliasAnalysisCounter.cpp
AliasAnalysisEvaluator.cpp
AliasDebugger.cpp
AliasSetTracker.cpp
Analysis.cpp	This patch breaks up Wrap.h so that it does not have to include all of	2013-05-01 20:59:00 +00:00
BasicAliasAnalysis.cpp	Make BasicAliasAnalysis recognize the fact a noalias argument cannot alias another argument, even if the other argument is not itself marked noalias.	2013-05-28 08:17:48 +00:00
BlockFrequencyInfo.cpp	BlockFrequency: Bump up the entry frequency a bit.	2013-06-25 13:34:40 +00:00
BranchProbabilityInfo.cpp	Use SmallVectorImpl::iterator/const_iterator instead of SmallVector to avoid specifying the vector size.	2013-07-04 01:31:24 +00:00
CaptureTracking.cpp	Extend 'readonly' and 'readnone' to work on function arguments as well as	2013-07-06 00:29:58 +00:00
CFGPrinter.cpp
CMakeLists.txt
CodeMetrics.cpp
ConstantFolding.cpp
CostModel.cpp
DependenceAnalysis.cpp	git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185187 91177308-0d34-0410-b5e6-96231b3b80d8	2013-06-28 18:44:48 +00:00
DominanceFrontier.cpp
DomPrinter.cpp
InstCount.cpp
InstructionSimplify.cpp
Interval.cpp
IntervalPartition.cpp
IVUsers.cpp
LazyValueInfo.cpp	Use SmallVectorImpl::iterator/const_iterator instead of SmallVector to avoid specifying the vector size.	2013-07-04 01:31:24 +00:00
LibCallAliasAnalysis.cpp
LibCallSemantics.cpp
Lint.cpp
LLVMBuild.txt
Loads.cpp
LoopInfo.cpp	Add support for llvm.vectorizer metadata	2013-05-28 20:00:34 +00:00
LoopPass.cpp
Makefile
MemDepPrinter.cpp
MemoryBuiltins.cpp	Added support for the Builtin attribute.	2013-06-27 00:25:01 +00:00
MemoryDependenceAnalysis.cpp	Fix xemacs mode line, don't put them in .cpp files (just header files). No	2013-06-10 23:10:59 +00:00
ModuleDebugInfoPrinter.cpp
NoAliasAnalysis.cpp
PathNumbering.cpp
PathProfileInfo.cpp
PathProfileVerifier.cpp
PHITransAddr.cpp
PostDominators.cpp
ProfileDataLoader.cpp
ProfileDataLoaderPass.cpp
ProfileEstimatorPass.cpp	Use SmallVectorImpl::iterator/const_iterator instead of SmallVector to avoid specifying the vector size.	2013-07-04 01:31:24 +00:00
ProfileInfo.cpp
ProfileInfoLoader.cpp
ProfileInfoLoaderPass.cpp
ProfileVerifierPass.cpp
PtrUseVisitor.cpp
README.txt
RegionInfo.cpp	RegionInfo: Do not crash if unreachable block is found	2013-05-03 15:48:34 +00:00
RegionPass.cpp
RegionPrinter.cpp
ScalarEvolution.cpp	Fix a SCEV update problem.	2013-07-08 17:33:13 +00:00
ScalarEvolutionAliasAnalysis.cpp
ScalarEvolutionExpander.cpp
ScalarEvolutionNormalization.cpp
SparsePropagation.cpp
TargetTransformInfo.cpp	Loop Strength Reduce: Scaling factor cost.	2013-05-31 21:29:03 +00:00
Trace.cpp
TypeBasedAliasAnalysis.cpp
ValueTracking.cpp	isKnownToBeAPowerOfTwo: Fix a typo in a comment	2013-07-06 02:24:59 +00:00

README.txt

Analysis Opportunities:

//===---------------------------------------------------------------------===//

In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:

  {1,+,3,+,2}<loop>

Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as

  (-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))

In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.

//===---------------------------------------------------------------------===//

In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,

ScalarEvolution is forming this expression:

((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))

This could be folded to

(-1 * (trunc i64 undef to i32))

//===---------------------------------------------------------------------===//