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.
  • The DEBUG macro has been renamed to LLVM_DEBUG, the interface remains the same. If you used this macro you need to migrate to the new one. You should also clang-format your code to make it easier to integrate future changes locally. This can be done with the following bash commands:
git grep -l 'DEBUG' | xargs perl -pi -e 's/\bDEBUG\s?\(/LLVM_DEBUG(/g'
git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM
  • Early support for UBsan, X-Ray instrumentation and libFuzzer (x86 and x86_64) for OpenBSD. Support for MSan (x86_64), X-Ray instrumentation and libFuzzer (x86 and x86_64) for FreeBSD.
  • 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

During this release …

Changes to the PowerPC Target

During this release …

Changes to the X86 Target

During this release …

Changes to the AMDGPU Target

During this release …

Changes to the AVR Target

During this release …

Changes to the OCaml bindings

  • Remove add_bb_vectorize.

Changes to the C API

  • Remove LLVMAddBBVectorizePass. The implementation was removed and the C interface was made a deprecated no-op in LLVM 5. Use LLVMAddSLPVectorizePass instead to get the supported SLP vectorizer.

Changes to the DAG infrastructure

  • ADDC/ADDE/SUBC/SUBE are now deprecated and will default to expand. Backends that wish to continue to use these opcodes should explicitely request so using setOperationAction in their TargetLowering. New backends should use UADDO/ADDCARRY/USUBO/SUBCARRY instead of the deprecated opcodes.
  • The SETCCE opcode has now been removed in favor of SETCCCARRY.

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.

If you have any questions or comments about LLVM, please feel free to contact us via the mailing lists.