8d487668d0
Yes, if operands are non-positive this comes at the extra cost of two extra negations. But a. division is already just ridiculously costly, two more subtractions can't hurt much :) and b. we have better/more analyzes/folds for an unsigned division, we could end up narrowing it's bitwidth, converting it to lshr, etc. This is essentially a take two on 0fdcca07ad2c0bdc2cdd40ba638109926f4f513b, which didn't fix the potential regression i was seeing, because ValueTracking's computeKnownBits() doesn't make use of dominating conditions in it's analysis. While i could teach it that, this seems like the more general fix. This big hammer actually does catch said potential regression. Over vanilla test-suite + RawSpeed + darktable (10M IR instrs, 1M IR BB, 1M X86 ASM instrs), this fires/converts 5 more (+2%) SDiv's, the total instruction count at the end of middle-end pipeline is only +6, so out of +10 extra negations, ~half are folded away, and asm instr count is only +1, so practically speaking all extra negations are folded away and are therefore free. Sadly, all these new UDiv's remained, none folded away. But there are two less basic blocks. https://rise4fun.com/Alive/VS6 Name: v0 Pre: C0 >= 0 && C1 >= 0 %r = sdiv i8 C0, C1 => %r = udiv i8 C0, C1 Name: v1 Pre: C0 <= 0 && C1 >= 0 %r = sdiv i8 C0, C1 => %t0 = udiv i8 -C0, C1 %r = sub i8 0, %t0 Name: v2 Pre: C0 >= 0 && C1 <= 0 %r = sdiv i8 C0, C1 => %t0 = udiv i8 C0, -C1 %r = sub i8 0, %t0 Name: v3 Pre: C0 <= 0 && C1 <= 0 %r = sdiv i8 C0, C1 => %r = udiv i8 -C0, -C1
The LLVM Compiler Infrastructure
This directory and its sub-directories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.
The README briefly describes how to get started with building LLVM. For more information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Getting Started with the LLVM System
Taken from https://llvm.org/docs/GettingStarted.html.
Overview
Welcome to the LLVM project!
The LLVM project has multiple components. The core of the project is itself called "LLVM". This contains all of the tools, libraries, and header files needed to process intermediate representations and converts it into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer. It also contains basic regression tests.
C-like languages use the Clang front end. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
Getting the Source Code and Building LLVM
The LLVM Getting Started documentation may be out of date. The Clang Getting Started page might have more accurate information.
This is an example work-flow and configuration to get and build the LLVM source:
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Checkout LLVM (including related sub-projects like Clang):
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git clone https://github.com/llvm/llvm-project.git -
Or, on windows,
git clone --config core.autocrlf=false https://github.com/llvm/llvm-project.git
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Configure and build LLVM and Clang:
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cd llvm-project -
mkdir build -
cd build -
cmake -G <generator> [options] ../llvmSome common build system generators are:
Ninja--- for generating Ninja build files. Most llvm developers use Ninja.Unix Makefiles--- for generating make-compatible parallel makefiles.Visual Studio--- for generating Visual Studio projects and solutions.Xcode--- for generating Xcode projects.
Some Common options:
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-DLLVM_ENABLE_PROJECTS='...'--- semicolon-separated list of the LLVM sub-projects you'd like to additionally build. Can include any of: clang, clang-tools-extra, libcxx, libcxxabi, libunwind, lldb, compiler-rt, lld, polly, or debuginfo-tests.For example, to build LLVM, Clang, libcxx, and libcxxabi, use
-DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi". -
-DCMAKE_INSTALL_PREFIX=directory--- Specify for directory the full path name of where you want the LLVM tools and libraries to be installed (default/usr/local). -
-DCMAKE_BUILD_TYPE=type--- Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug. -
-DLLVM_ENABLE_ASSERTIONS=On--- Compile with assertion checks enabled (default is Yes for Debug builds, No for all other build types).
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cmake --build . [-- [options] <target>]or your build system specified above directly.-
The default target (i.e.
ninjaormake) will build all of LLVM. -
The
check-alltarget (i.e.ninja check-all) will run the regression tests to ensure everything is in working order. -
CMake will generate targets for each tool and library, and most LLVM sub-projects generate their own
check-<project>target. -
Running a serial build will be slow. To improve speed, try running a parallel build. That's done by default in Ninja; for
make, use the option-j NNN, whereNNNis the number of parallel jobs, e.g. the number of CPUs you have.
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For more information see CMake
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Consult the Getting Started with LLVM page for detailed information on configuring and compiling LLVM. You can visit Directory Layout to learn about the layout of the source code tree.