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Roman Lebedev 6efaf72ba7 [InstCombine] canShiftBinOpWithConstantRHS(): drop bogus signbit check
Summary:
In D61918 i was looking at dropping it in DAGCombiner `visitShiftByConstant()`,
but as @craig.topper pointed out, it was copied from here.

That check claims that the transform is illegal otherwise.
That isn't true:
1. For `ISD::ADD`, we only process `ISD::SHL` outer shift => sign bit does not matter
   https://rise4fun.com/Alive/K4A
2. For `ISD::AND`, there is no restriction on constants:
   https://rise4fun.com/Alive/Wy3
3. For `ISD::OR`, there is no restriction on constants:
   https://rise4fun.com/Alive/GOH
3. For `ISD::XOR`, there is no restriction on constants:
   https://rise4fun.com/Alive/ml6

So, why is it there then?
As far as i can tell, it dates all the way back to original check-in rL7793.
I think we should just drop it.

Reviewers: spatel, craig.topper, efriedma, majnemer

Reviewed By: spatel

Subscribers: llvm-commits, craig.topper

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61938

llvm-svn: 361043
2019-05-17 15:52:49 +00:00
benchmarks Pull google/benchmark library to the LLVM tree 2018-08-28 09:42:41 +00:00
bindings [OCaml] Update api to account for FNeg and CallBr instructions 2019-04-16 15:00:19 +00:00
cmake [Analysis] Only run plugins tests if plugins are actually enabled 2019-05-17 06:07:37 +00:00
docs [ELF] Implement Dependent Libraries Feature 2019-05-17 03:44:15 +00:00
examples [JITLink] Update BuildingAJIT tutorials to account for API changes in r358818. 2019-04-20 17:35:28 +00:00
include GlobalISel: Fix missing version of customFor 2019-05-17 11:49:41 +00:00
lib [InstCombine] canShiftBinOpWithConstantRHS(): drop bogus signbit check 2019-05-17 15:52:49 +00:00
projects Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
resources
runtimes [CMake] Replace the sanitizer support in runtimes build with multilib 2019-04-22 23:31:39 +00:00
test [InstCombine] canShiftBinOpWithConstantRHS(): drop bogus signbit check 2019-05-17 15:52:49 +00:00
tools [ELF] Implement Dependent Libraries Feature 2019-05-17 03:44:15 +00:00
unittests GlobalISel: Add fp<->int casts to MachineIRBuilder 2019-05-17 11:49:39 +00:00
utils Fix GN build 2019-05-16 00:19:37 +00:00
.arcconfig
.clang-format
.clang-tidy Disable tidy checks with too many hits 2019-02-01 11:20:13 +00:00
.gitattributes [DebugInfo] Add DILabel metadata and intrinsic llvm.dbg.label. 2018-05-09 02:40:45 +00:00
.gitignore [clangd] Store index in '.clangd/index' instead of '.clangd-index' 2019-02-20 19:08:06 +00:00
CMakeLists.txt build: add option to disable unwind tables 2019-05-02 19:37:26 +00:00
CODE_OWNERS.TXT [llvm-mca] Move llvm-mca library to llvm/lib/MCA. 2018-12-17 08:08:31 +00:00
configure
CREDITS.TXT add Qiu Chaofan (qiucf@cn.ibm.com) to the CREDITS.txt 2019-04-23 02:37:48 +00:00
LICENSE.TXT Fix typos throughout the license files that somehow I and my reviewers 2019-01-21 09:52:34 +00:00
llvm.spec.in Update structured references to the license to the new license. 2019-01-19 11:30:51 +00:00
LLVMBuild.txt Update the file headers across all of the LLVM projects in the monorepo 2019-01-19 08:50:56 +00:00
README.txt Testing commit access 2019-02-19 20:38:51 +00:00
RELEASE_TESTERS.TXT Update the list of platforms & archs 2018-12-16 14:47:16 +00:00

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