LLVM 7.0.0 Release Notes

Warning

These are in-progress notes for the upcoming LLVM 7 release. Release notes for previous releases can be found on the Download Page.

Introduction

This document contains the release notes for the LLVM Compiler Infrastructure, release 7.0.0. Here we describe the status of LLVM, including major improvements from the previous release, improvements in various subprojects of LLVM, and some of the current users of the code. All LLVM releases may be downloaded from the LLVM releases web site.

For more information about LLVM, including information about the latest release, please check out the main LLVM web site. If you have questions or comments, the LLVM Developer’s Mailing List is a good place to send them.

Note that if you are reading this file from a Subversion checkout or the main LLVM web page, this document applies to the next release, not the current one. To see the release notes for a specific release, please see the releases page.

Non-comprehensive list of changes in this release

  • Libraries have been renamed from 7.0 to 7. This change also impacts downstream libraries like lldb.
  • The LoopInstSimplify pass (-loop-instsimplify) has been removed.
  • Symbols starting with ? are no longer mangled by LLVM when using the Windows x or w IR mangling schemes.
  • A new tool named llvm-exegesis has been added. llvm-exegesis automatically measures instruction scheduling properties (latency/uops) and provides a principled way to edit scheduling models.
  • A new tool named llvm-mca has been added. llvm-mca is a static performance analysis tool that uses information available in LLVM to statically predict the performance of machine code for a specific CPU.
  • The optimization flag to merge constants (-fmerge-all-constants) is no longer applied by default.
  • Optimization of floating-point casts is improved. This may cause surprising results for code that is relying on the undefined behavior of overflowing casts. The optimization can be disabled by specifying a function attribute: “strict-float-cast-overflow”=”false”. This attribute may be created by the clang option -fno-strict-float-cast-overflow. Code sanitizers can be used to detect affected patterns. The option for detecting this problem alone is “-fsanitize=float-cast-overflow”:
int main() {
  float x = 4294967296.0f;
  x = (float)((int)x);
  printf("junk in the ftrunc: %f\n", x);
  return 0;
}
clang -O1 ftrunc.c -fsanitize=float-cast-overflow ; ./a.out
ftrunc.c:5:15: runtime error: 4.29497e+09 is outside the range of representable values of type 'int'
junk in the ftrunc: 0.000000
  • LLVM_ON_WIN32 is no longer set by llvm/Config/config.h and llvm/Config/llvm-config.h. If you used this macro, use the compiler-set _WIN32 instead which is set exactly when LLVM_ON_WIN32 used to be set.
  • Note..

Changes to the LLVM IR

  • The signatures for the builtins @llvm.memcpy, @llvm.memmove, and @llvm.memset have changed. Alignment is no longer an argument, and are instead conveyed as parameter attributes.
  • invariant.group.barrier has been renamed to launder.invariant.group.
  • invariant.group metadata can now refer only empty metadata nodes.

Changes to the ARM Backend

During this release …

Changes to the MIPS Target

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Changes to the PowerPC Target

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Changes to the X86 Target

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Changes to the AMDGPU Target

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Changes to the AVR Target

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Changes to the OCaml bindings

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Changes to the C API

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Additional Information

A wide variety of additional information is available on the LLVM web page, in particular in the documentation section. The web page also contains versions of the API documentation which is up-to-date with the Subversion version of the source code. You can access versions of these documents specific to this release by going into the llvm/docs/ directory in the LLVM tree.

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