llvm-6502

mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-10-17 19:25:48 +00:00

History

Andrew Trick 64925c55c6 Enable LSR IV Chains with sufficient heuristics. These heuristics are sufficient for enabling IV chains by default. Performance analysis has been done for i386, x86_64, and thumbv7. The optimization is rarely important, but can significantly speed up certain cases by eliminating spill code within the loop. Unrolled loops are prime candidates for IV chains. In many cases, the final code could still be improved with more target specific optimization following LSR. The goal of this feature is for LSR to make the best choice of induction variables. Instruction selection may not completely take advantage of this feature yet. As a result, there could be cases of slight code size increase. Code size can be worse on x86 because it doesn't support postincrement addressing. In fact, when chains are formed, you may see redundant address plus stride addition in the addressing mode. GenerateIVChains tries to compensate for the common cases. On ARM, code size increase can be mitigated by using postincrement addressing, but downstream codegen currently misses some opportunities. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147826 91177308-0d34-0410-b5e6-96231b3b80d8		2012-01-10 01:45:08 +00:00
..
IPA
AliasAnalysis.cpp
AliasAnalysisCounter.cpp
AliasAnalysisEvaluator.cpp
AliasDebugger.cpp
AliasSetTracker.cpp
Analysis.cpp
BasicAliasAnalysis.cpp
BlockFrequencyInfo.cpp	Add some constantness to BranchProbabilityInfo and BlockFrequnencyInfo.	2011-12-20 20:03:10 +00:00
BranchProbabilityInfo.cpp	Make the unreachable probability much much heavier. The previous	2011-12-22 09:26:37 +00:00
CaptureTracking.cpp	Change CaptureTracking to pass a Use* instead of a Value* when a value is	2011-12-28 23:24:21 +00:00
CFGPrinter.cpp
CMakeLists.txt
ConstantFolding.cpp
DbgInfoPrinter.cpp
DebugInfo.cpp	Unweaken vtables as per http://llvm.org/docs/CodingStandards.html#ll_virtual_anch	2011-12-20 02:50:00 +00:00
DIBuilder.cpp	Update language check. Do not ignore DW_LANG_Python.	2012-01-09 17:49:47 +00:00
DominanceFrontier.cpp	Unweaken vtables as per http://llvm.org/docs/CodingStandards.html#ll_virtual_anch	2011-12-20 02:50:00 +00:00
DomPrinter.cpp
InlineCost.cpp	Continue counting intrinsics as instructions (except when they aren't, such as	2011-12-21 20:26:03 +00:00
InstCount.cpp
InstructionSimplify.cpp	PatternMatch: Introduce a matcher for instructions with the "exact" bit. Use it to simplify a few matchers.	2012-01-01 17:55:30 +00:00
Interval.cpp
IntervalPartition.cpp
IVUsers.cpp	Put all IVUsers in the processed set. Allow querying IVUsers with isIVUserOrOperand.	2012-01-06 21:41:55 +00:00
LazyValueInfo.cpp
LibCallAliasAnalysis.cpp
LibCallSemantics.cpp
Lint.cpp
LLVMBuild.txt	LLVMBuild: Introduce a common section which currently has a list of the	2011-12-12 22:45:54 +00:00
Loads.cpp
LoopDependenceAnalysis.cpp
LoopInfo.cpp	Move Instruction::isSafeToSpeculativelyExecute out of VMCore and	2011-12-14 23:49:11 +00:00
LoopPass.cpp
Makefile
MemDepPrinter.cpp	Fix a stupid typo in MemDepPrinter.	2011-12-14 02:54:39 +00:00
MemoryBuiltins.cpp
MemoryDependenceAnalysis.cpp	Change CaptureTracking to pass a Use* instead of a Value* when a value is	2011-12-28 23:24:21 +00:00
ModuleDebugInfoPrinter.cpp
NoAliasAnalysis.cpp
PathNumbering.cpp
PathProfileInfo.cpp
PathProfileVerifier.cpp
PHITransAddr.cpp	Move Instruction::isSafeToSpeculativelyExecute out of VMCore and	2011-12-14 23:49:11 +00:00
PostDominators.cpp
ProfileEstimatorPass.cpp
ProfileInfo.cpp
ProfileInfoLoader.cpp
ProfileInfoLoaderPass.cpp
ProfileVerifierPass.cpp
README.txt
RegionInfo.cpp
RegionPass.cpp
RegionPrinter.cpp
ScalarEvolution.cpp	Expose isNonConstantNegative to users of ScalarEvolution.	2012-01-07 00:27:31 +00:00
ScalarEvolutionAliasAnalysis.cpp
ScalarEvolutionExpander.cpp	Enable LSR IV Chains with sufficient heuristics.	2012-01-10 01:45:08 +00:00
ScalarEvolutionNormalization.cpp
SparsePropagation.cpp
Trace.cpp
TypeBasedAliasAnalysis.cpp
ValueTracking.cpp	Generalize isSafeToSpeculativelyExecute to work on arbitrary	2012-01-04 23:01:09 +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))

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