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LLVM backend for 6502
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fb57392a8d
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Quentin Colombet fb57392a8d [RegAlloc] Make tryInstructionSplit less aggressive. 
The greedy register allocator tries to split a live-range around each
instruction where it is used or defined to relax the constraints on the entire
live-range (this is a last chance split before falling back to spill).
The goal is to have a big live-range that is unconstrained (i.e., that can use
the largest legal register class) and several small local live-range that carry
the constraints implied by each instruction.
E.g.,
Let csti be the constraints on operation i.

V1=
op1 V1(cst1)
op2 V1(cst2)

V1 live-range is constrained on the intersection of cst1 and cst2.

tryInstructionSplit relaxes those constraints by aggressively splitting each
def/use point:
V1=
V2 = V1
V3 = V2
op1 V3(cst1)
V4 = V2
op2 V4(cst2)

Because of how the coalescer infrastructure works, each new variable (V3, V4)
that is alive at the same time as V1 (or its copy, here V2) interfere with V1.
Thus, we end up with an uncoalescable copy for each split point.

To make tryInstructionSplit less aggressive, we check if the split point
actually relaxes the constraints on the whole live-range. If it does not, we do
not insert it.
Indeed, it will not help the global allocation problem:
- V1 will have the same constraints.
- V1 will have the same interference + possibly the newly added split variable
  VS.
- VS will produce an uncoalesceable copy if alive at the same time as V1.

<rdar://problem/15570057>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198369 91177308-0d34-0410-b5e6-96231b3b80d8
2014-01-02 22:47:22 +00:00
autoconf Update the copyright credits -- Happy new year 2014! 2014-01-01 08:27:31 +00:00
bindings Makefile.ocaml: Tweak to use --system-libs. 2013-12-20 00:36:59 +00:00
cmake [CMake] Add missing set_output_directory after Takumi's change in r198205. 2014-01-02 19:47:45 +00:00
docs Remove the 's' DataLayout specification 2014-01-01 22:29:43 +00:00
examples [CMake] Update LLVM_LINK_COMPONENTS for each CMakeLists.txt. 2013-12-10 11:13:32 +00:00
include [RegAlloc] Make tryInstructionSplit less aggressive. 2014-01-02 22:47:22 +00:00
lib [RegAlloc] Make tryInstructionSplit less aggressive. 2014-01-02 22:47:22 +00:00
projects Revert "Revert "Windows: Add support for unicode command lines"" 2013-10-07 01:00:07 +00:00
test [RegAlloc] Make tryInstructionSplit less aggressive. 2014-01-02 22:47:22 +00:00
tools Port r198087 and r198089 (strip dead code by default) from make to cmake. 2013-12-30 03:36:05 +00:00
unittests Make llvm::Regex non-copyable but movable. 2014-01-02 19:04:59 +00:00
utils [TableGen] Handle ValueType in CodeGenDAGPatterns GetNumNodeResults 2014-01-02 20:47:05 +00:00
.arcconfig Add .arcconfig to the repository. Useful if someone wants to use phabricator's command line tool. 2012-12-01 12:07:58 +00:00
.clang-format Add a clang-format file so that the tool can automatically detect the 2013-09-02 07:19:04 +00:00
.gitignore Add extra vim swap file pattern 2012-10-09 23:48:34 +00:00
CMakeLists.txt [CMake][VS][XCode] Restruct the output directory layout more comfortable, ${BINARY_DIR}/${BUILD_MODE}/(bin|lib) 2013-12-30 06:48:30 +00:00
CODE_OWNERS.TXT Update email address. 2013-12-04 09:42:49 +00:00
configure Update the copyright credits -- Happy new year 2014! 2014-01-01 08:27:31 +00:00
CREDITS.TXT Fix documentation typos 2013-12-20 00:33:39 +00:00
LICENSE.TXT Update the copyright credits -- Happy new year 2014! 2014-01-01 08:27:31 +00:00
llvm.spec.in
LLVMBuild.txt Remove the very substantial, largely unmaintained legacy PGO 2013-10-02 15:42:23 +00:00
Makefile llvm-config: Fixup r197380, tweak for cross compilation. SYSTEM_LIBS should be --host's in BuildTools/llvm-config. 2013-12-16 13:09:06 +00:00
Makefile.common Makefile.common: Update a description, s/Source/SOURCES/ , according to MakefileGuide.html#control-variables . 2012-12-07 01:43:23 +00:00
Makefile.config.in Add an autoconf option for turning on -gsplit-dwarf by default 2013-06-25 01:12:25 +00:00
Makefile.rules Strip dead code when linking by default with BFD ld (linux, ...) and ld64 (os x). 2013-12-27 22:38:59 +00:00
README.txt Revert "Test commit to check e-mail address. Please discard this." 2013-10-04 10:59:13 +00:00

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