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llvm-project/llvm/lib/CodeGen/SelectionDAG
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Reid Kleckner f7c0980c10 Elide argument copies during instruction selection 
Summary:
Avoids tons of prologue boilerplate when arguments are passed in memory
and left in memory. This can happen in a debug build or in a release
build when an argument alloca is escaped.  This will dramatically affect
the code size of x86 debug builds, because X86 fast isel doesn't handle
arguments passed in memory at all. It only handles the x86_64 case of up
to 6 basic register parameters.

This is implemented by analyzing the entry block before ISel to identify
copy elision candidates. A copy elision candidate is an argument that is
used to fully initialize an alloca before any other possibly escaping
uses of that alloca. If an argument is a copy elision candidate, we set
a flag on the InputArg. If the the target generates loads from a fixed
stack object that matches the size and alignment requirements of the
alloca, the SelectionDAG builder will delete the stack object created
for the alloca and replace it with the fixed stack object. The load is
left behind to satisfy any remaining uses of the argument value. The
store is now dead and is therefore elided. The fixed stack object is
also marked as mutable, as it may now be modified by the user, and it
would be invalid to rematerialize the initial load from it.

Supersedes D28388

Fixes PR26328

Reviewers: chandlerc, MatzeB, qcolombet, inglorion, hans

Subscribers: igorb, llvm-commits

Differential Revision: https://reviews.llvm.org/D29668

llvm-svn: 296683
 		2017-03-01 21:42:00 +00:00
..
CMakeLists.txt [CMake] NFC. Updating CMake dependency specifications 2016-11-17 04:36:50 +00:00
DAGCombiner.cpp [DAG] Prevent Stale nodes from entering worklist 2017-03-01 20:19:38 +00:00
FastISel.cpp [CodeGen] Fix some Clang-tidy modernize and Include What You Use warnings; other minor fixes (NFC). 2017-02-27 22:45:06 +00:00
FunctionLoweringInfo.cpp Simplify FunctionLoweringInfo.cpp with range for loops 2016-12-30 00:21:38 +00:00
InstrEmitter.cpp Removing a redundant assignment 2017-02-14 14:44:01 +00:00
InstrEmitter.h Pass DebugLoc and SDLoc by const ref. 2016-06-12 15:39:02 +00:00
LLVMBuild.txt
…
LegalizeDAG.cpp Use SelectionDAG::getBuildVector helper function where possible. NFCI. 2017-01-30 18:53:45 +00:00
LegalizeFloatTypes.cpp [legalizetypes] Push fp16 -> fp32 extension node to worklist. 2017-02-01 13:01:33 +00:00
LegalizeIntegerTypes.cpp Remove unused CONVERT_RNDSAT intrinsics 2017-01-10 22:38:02 +00:00
LegalizeTypes.cpp [legalizetypes] Push fp16 -> fp32 extension node to worklist. 2017-02-01 13:01:33 +00:00
LegalizeTypes.h [SelectionDAG] Add scalarization support for ISD::*_EXTEND_VECTOR_INREG opcodes. 2017-02-20 11:55:58 +00:00
LegalizeTypesGeneric.cpp Do not assume that FP vector operands are never legalized by expanding 2016-10-26 19:51:35 +00:00
LegalizeVectorOps.cpp DAG: Do not scalarize fsub if fneg is legal 2017-02-15 22:02:42 +00:00
LegalizeVectorTypes.cpp [SelectionDAG] Add scalarization support for ISD::*_EXTEND_VECTOR_INREG opcodes. 2017-02-20 11:55:58 +00:00
ResourcePriorityQueue.cpp Add iterator_range<regclass_iterator> to {Target,MC}RegisterInfo, NFC 2017-01-25 19:29:04 +00:00
SDNodeDbgValue.h Apply clang-tidy's misc-move-constructor-init throughout LLVM. 2016-05-27 14:27:24 +00:00
ScheduleDAGFast.cpp
…
ScheduleDAGRRList.cpp Cleanup dump() functions. 2017-01-28 02:02:38 +00:00
ScheduleDAGSDNodes.cpp Remove redundant call to GluedNodes.back() [NFC] 2017-02-19 16:56:18 +00:00
ScheduleDAGSDNodes.h [Target] Fix some Clang-tidy modernize and Include What You Use warnings; other minor fixes (NFC). 2017-01-11 01:45:03 +00:00
ScheduleDAGVLIW.cpp
…
SelectionDAG.cpp [DAGCombine] Allow vector constant folding of any value type before type legalization 2017-02-10 14:37:25 +00:00
SelectionDAGBuilder.cpp Elide argument copies during instruction selection 2017-03-01 21:42:00 +00:00
SelectionDAGBuilder.h Add intrinsics for constrained floating point operations 2017-01-26 23:27:59 +00:00
SelectionDAGDumper.cpp Cleanup dump() functions. 2017-01-28 02:02:38 +00:00
SelectionDAGISel.cpp Elide argument copies during instruction selection 2017-03-01 21:42:00 +00:00
SelectionDAGPrinter.cpp
…
SelectionDAGTargetInfo.cpp Rename TargetSelectionDAGInfo into SelectionDAGTargetInfo and move it to CodeGen/ 2016-01-27 16:32:26 +00:00
StatepointLowering.cpp [Statepoints] Reuse stack slots more than once within a basic block 2016-12-13 01:21:15 +00:00
StatepointLowering.h [NFC] Header cleanup 2016-04-18 09:17:29 +00:00
TargetLowering.cpp [TargetLowering] fix SETCC SETLT folding with FP types 2017-02-12 23:07:52 +00:00