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Sanjay Patel d66607bd8c [CodeGenPrepare] use branch weight metadata to decide if a select should be turned into a branch 
This is part of solving PR27344:
https://llvm.org/bugs/show_bug.cgi?id=27344

CGP should undo the SimplifyCFG transform for the same reason that earlier patches have used this
same mechanism: it's possible that passes between SimplifyCFG and CGP may be able to optimize the
IR further with a select in place.

For the TLI hook default, >99% taken or not taken is chosen as the default threshold for a highly
predictable branch. Even the most limited HW branch predictors will be correct on this branch almost
all the time, so even a massive mispredict penalty perf loss would be overcome by the win from all
the times the branch was predicted correctly.

As a follow-up, we could make the default target hook less conservative by using the SchedMachineModel's
MispredictPenalty. Or we could just let targets override the default by implementing the hook with that
and other target-specific options. Note that trying to statically determine mispredict rates for 
close-to-balanced profile weight data is generally impossible if the HW is sufficiently advanced. Ie, 
50/50 taken/not-taken might still be 100% predictable.

Finally, note that this patch as-is will not solve PR27344 because the current __builtin_unpredictable()
branch weight default values are 4 and 64. A proposal to change that is in D19435.

Differential Revision: http://reviews.llvm.org/D19488

llvm-svn: 267572
 		2016-04-26 17:11:17 +00:00
..
AsmWriter.cpp IR: Avoid mallocs in constructor of ModuleSlotTracker 2016-04-20 19:05:59 +00:00
AttributeImpl.h Add the allocsize attribute to LLVM. 2016-04-12 01:05:35 +00:00
Attributes.cpp Attempt to make buildbot happier with r266032. 2016-04-12 01:44:13 +00:00
AttributesCompatFunc.td Provide a way to specify inliner's attribute compatibility and merging. 2015-12-22 23:57:37 +00:00
AutoUpgrade.cpp [AArch64] [ARM] Make a target-independent llvm.thread.pointer intrinsic. 2016-04-19 20:51:05 +00:00
BasicBlock.cpp Introduce @llvm.experimental.deoptimize 2016-03-11 19:08:34 +00:00
CMakeLists.txt Re-commit optimization bisect support (r267022) without new pass manager support. 2016-04-22 22:06:11 +00:00
Comdat.cpp
…
ConstantFold.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
ConstantFold.h [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
ConstantRange.cpp [ConstantRange] Generalize makeGuaranteedNoWrapRegion to work on ranges 2016-03-03 18:31:16 +00:00
Constants.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
ConstantsContext.h Increase SmallVector size for ConstantUniqueMap::getHashValue() (NFC) 2016-04-19 00:17:55 +00:00
Core.cpp Reformat LLVMConstPointerNull. NFC 2016-04-25 22:23:35 +00:00
DIBuilder.cpp DebugInfo: Change DIBuilder to make distinct DIGlobalVariables 2016-04-23 22:29:09 +00:00
DataLayout.cpp Replace Type::getInt32Ty() and comparison by isIntegerTy(32). NFC. 2016-01-22 03:30:27 +00:00
DebugInfo.cpp DebugInfo: Remove MDString-based type references 2016-04-23 21:08:00 +00:00
DebugInfoMetadata.cpp DebugInfo: Remove MDString-based type references 2016-04-23 21:08:00 +00:00
DebugLoc.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
DiagnosticInfo.cpp Refactor backend diagnostics for unsupported features 2016-02-02 13:52:43 +00:00
DiagnosticPrinter.cpp MIR Serialization: Connect the machine function analysis pass to the MIR parser. 2015-06-15 20:30:22 +00:00
Dominators.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
Function.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
GCOV.cpp llvm-cov: Fix reading gcov data that does not have function names 2016-02-08 22:49:40 +00:00
GVMaterializer.cpp
…
Globals.cpp [GCC] Attribute ifunc support in llvm 2016-04-07 12:32:19 +00:00
IRBuilder.cpp Revert "Support arbitrary addrspace pointers in masked load/store intrinsics" 2016-04-14 08:47:17 +00:00
IRPrintingPasses.cpp Recommit r256952 "Filtering IR printing for print-after-all/print-before-all" 2016-01-06 22:55:03 +00:00
InlineAsm.cpp Fix SEGV in InlineAsm::ConstraintInfo::Parse. 2015-09-03 15:41:37 +00:00
Instruction.cpp [GVN] Respect fast-math-flags on fcmps 2016-04-22 06:37:51 +00:00
Instructions.cpp [CodeGenPrepare] use branch weight metadata to decide if a select should be turned into a branch 2016-04-26 17:11:17 +00:00
IntrinsicInst.cpp IR: Add DbgInfoIntrinsic::getVariableLocation 2016-03-29 18:56:03 +00:00
LLVMBuild.txt
…
LLVMContext.cpp Re-commit optimization bisect support (r267022) without new pass manager support. 2016-04-22 22:06:11 +00:00
LLVMContextImpl.cpp Re-commit optimization bisect support (r267022) without new pass manager support. 2016-04-22 22:06:11 +00:00
LLVMContextImpl.h DebugInfo: Remove MDString-based type references 2016-04-23 21:08:00 +00:00
LegacyPassManager.cpp Annotate dump() methods with LLVM_DUMP_METHOD, addressing Richard Smith r259192 post commit comment. 2016-01-29 20:50:44 +00:00
MDBuilder.cpp [MDBuilder] Simplify code using initializer lists. NFC. 2015-11-22 18:03:17 +00:00
Mangler.cpp Update to use new name alignTo(). 2016-01-14 21:06:47 +00:00
Metadata.cpp [CodeGenPrepare] use branch weight metadata to decide if a select should be turned into a branch 2016-04-26 17:11:17 +00:00
MetadataImpl.h DI: Disallow uniquable DICompileUnits 2015-08-03 17:26:41 +00:00
Module.cpp [ThinLTO] Prevent importing of "llvm.used" values 2016-04-20 14:39:45 +00:00
ModuleSummaryIndex.cpp [ThinLTO] Introduce typedef for commonly-used map type (NFC) 2016-04-25 21:09:51 +00:00
Operator.cpp [opaque pointer types] [NFC] GEP: replace get(Pointer)ElementType uses with get{Source,Result}ElementType. 2016-01-19 17:28:00 +00:00
OptBisect.cpp Removing unused function. 2016-04-22 22:24:20 +00:00
Pass.cpp Re-commit optimization bisect support (r267022) without new pass manager support. 2016-04-22 22:06:11 +00:00
PassManager.cpp [PM] Implement the final conclusion as to how the analysis IDs should 2016-03-11 10:22:49 +00:00
PassRegistry.cpp [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
Statepoint.cpp Introduce an GCRelocateInst class [NFC] 2016-04-12 18:05:10 +00:00
SymbolTableListTraitsImpl.h IR: Remove implicit iterator conversions from lib/IR, NFC 2015-10-08 23:49:46 +00:00
Type.cpp [IR] Mark the Type subclass helper methods 'inline' and move their definitions to DerivedTypes.h so they can be inlined by the compiler. 2015-12-25 04:06:20 +00:00
TypeFinder.cpp Re-reapply "[IR] Move optional data in llvm::Function into a hungoff uselist" 2015-12-19 08:52:49 +00:00
Use.cpp Revert r240137 (Fixed/added namespace ending comments using clang-tidy. NFC) 2015-06-23 09:49:53 +00:00
User.cpp [IR] Teach `llvm::User` to co-allocate a descriptor. 2015-09-24 01:00:49 +00:00
Value.cpp Don't IPO over functions that can be de-refined 2016-04-08 00:48:30 +00:00
ValueSymbolTable.cpp Annotate dump() methods with LLVM_DUMP_METHOD, addressing Richard Smith r259192 post commit comment. 2016-01-29 20:50:44 +00:00
ValueTypes.cpp Add isScalarInteger helper to EVT/MVT 2016-03-01 18:01:28 +00:00
Verifier.cpp Verifier: Verify that each inlinable callsite of a debug-info-bearing function 2016-04-24 22:23:13 +00:00