llvm-6502

mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-12-12 13:30:51 +00:00

History

Andrew Trick 6f2ae41d21 Merge 183060: Prevent loop-unroll from making assumptions about undefined behavior. Fixes rdar:14036816, PR16130. There is an opportunity to compute precise trip counts for 'or' expressions and multi-exit loops. rdar:14038809: Optimize trip count computation for multi-exit loops. To do this we need to record the fact that ExitLimit assumes NSW. When it does not we can safely assume that the loop trip count is the minimum ExitLimt across all subexpressions and loop exits. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183060 91177308-0d34-0410-b5e6-96231b3b80d8 git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_33@183066 91177308-0d34-0410-b5e6-96231b3b80d8		2013-06-01 01:37:44 +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
AliasAnalysisCounter.cpp
AliasAnalysisEvaluator.cpp	Support in AAEvaluator to print alias queries of loads/stores with TBAA tags.	2013-03-22 22:34:41 +00:00
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	Revert r176408 and r176407 to address PR15540.	2013-04-09 18:16:05 +00:00
BlockFrequencyInfo.cpp
BranchProbabilityInfo.cpp
CaptureTracking.cpp
CFGPrinter.cpp
CMakeLists.txt
CodeMetrics.cpp
ConstantFolding.cpp	ConstantFolding: ComputeMaskedBits wants the scalar size for vectors.	2013-04-19 16:56:24 +00:00
CostModel.cpp	CostModel: Add parameter to instruction cost to further classify operand values	2013-04-04 23:26:21 +00:00
DependenceAnalysis.cpp
DominanceFrontier.cpp
DomPrinter.cpp
InstCount.cpp
InstructionSimplify.cpp	InstructionSimplify.cpp: Fix a ligature, "fi", to get rid of utf8 in comment.	2013-04-08 23:05:21 +00:00
Interval.cpp
IntervalPartition.cpp
IVUsers.cpp
LazyValueInfo.cpp
LibCallAliasAnalysis.cpp
LibCallSemantics.cpp
Lint.cpp
LLVMBuild.txt
Loads.cpp
LoopInfo.cpp
LoopPass.cpp
Makefile
MemDepPrinter.cpp
MemoryBuiltins.cpp	Revert r176408 and r176407 to address PR15540.	2013-04-09 18:16:05 +00:00
MemoryDependenceAnalysis.cpp	Fix unchecked uses of DominatorTree in MemoryDependenceAnalysis.	2013-05-06 02:07:24 +00:00
ModuleDebugInfoPrinter.cpp
NoAliasAnalysis.cpp
PathNumbering.cpp
PathProfileInfo.cpp
PathProfileVerifier.cpp	Build fixes for STLPort + GCC	2013-03-29 18:48:45 +00:00
PHITransAddr.cpp
PostDominators.cpp
ProfileDataLoader.cpp
ProfileDataLoaderPass.cpp
ProfileEstimatorPass.cpp
ProfileInfo.cpp	Build fixes for STLPort + GCC	2013-03-29 18:48:45 +00:00
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	Merge 183060: Prevent loop-unroll from making assumptions about undefined behavior.	2013-06-01 01:37:44 +00:00
ScalarEvolutionAliasAnalysis.cpp
ScalarEvolutionExpander.cpp
ScalarEvolutionNormalization.cpp
SparsePropagation.cpp
TargetTransformInfo.cpp	CostModel: Add parameter to instruction cost to further classify operand values	2013-04-04 23:26:21 +00:00
Trace.cpp
TypeBasedAliasAnalysis.cpp	Struct-path aware TBAA: change the format of TBAAStructType node.	2013-04-27 00:26:11 +00:00
ValueTracking.cpp

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))

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