May 12, 2026 - The LLVM code representation is designed to be used in three different forms: as an in-memory compiler IR, as an on-disk bitcode representation (suitable for fast loading by a Just-In-Time compiler), and as a human readable assembly language representation. This allows LLVM to provide a powerful intermediate representation for efficient compiler transformations and analysis, while providing a natural means to debug and visualize the transformations.

LLVM IR is well documented and… somewhat stable, which makes it a very good compilation target, since language implementers can re-use the thousands of engineer hours poured into LLVM already. The source of truth for “what is LLVM IR?” is the LangRef.

The LLVM code representation is designed to be used in three different forms: as an in-memory compiler IR, as an on-disk bitcode representation (suitable for fast loading by a Just-In-Time compiler), and as a human readable assembly language representation. This allows LLVM to provide a powerful intermediate representation for efficient compiler transformations and analysis, while providing a natural means to debug and visualize the transformations.

The LLVM Project is a collection of modular and reusable compiler and toolchain technologies. - llvm-project/mlir/docs/LangRef.md at main · llvm/llvm-project

android/toolchain/llvm/refs/heads/main/./docs/LangRef.rst ·

http://llvm.org/docs/LangRef.html · ● · Writing an LLVM Pass · – · http://llvm.org/docs/WritingAnLLVMPass.html · ● · LLVM’s Analysis and Transform Passes · – · http://llvm.org/docs/Passes.html · ● · LLVM Internal Documentation · – · http://llvm.org/docs/doxygen/html/ – ·

While you are playing around with generating or writing LLVM IR, you may want to add the option -fsanitize=undefined to Clang/Clang++ insofar you use either of those. This option makes Clang/Clang++ insert run-time checks in places where it would normally output an ud2 instruction.

Try the following on x86_64: -- 8< -- define i32 @test(i32 %X, ...) { ; Initialize variable argument processing %ap = alloca i8* %ap2 = bitcast i8** %ap to i8* call void @llvm.va_start(i8* %ap2) ; Read a single integer argument %tmp = va_arg i8** %ap, i32 ; Demonstrate usage of llvm.va_copy and llvm.va_end %aq = alloca i8* %aq2 = bitcast i8** %aq to i8* call void @llvm.va_copy(i8* %aq2, i8* %ap2) call void @llvm.va_end(i8* %aq2) ; Stop processing of arguments. call void @llvm.va_end(i8* %ap2) ret i32 %tmp } define i32 @main() { �ll = call i32 (i32, ...)* @test(i32 1, i32 3) ret i32 �ll } declare void @llvm.va_start(i8*) declare void @llvm.va_copy(i8*, i8*) declare void @llvm.va_end(i8*) -- 8< -- It happens because va_arg is apparently not implemented properly on X86 (I saw tests/Codegen/X86/vaargs.ll). What should be done about the situation? 1. Update the LangRef.

Dialects provide a modular way in which targets can expose target-specific operations directly through to MLIR. As an example, some targets go through LLVM. LLVM has a rich set of intrinsics for certain target-independent operations (e.g. addition with overflow check) as well as providing access to target-specific operations for the targets it supports (e.g.

June 10, 2021 - As the code base is really huge ... in LangRef. In such a case, many times I used gdb/lldb debugger tools for understanding the pipeline. Use debugging tools and identify the logic that is responsible for generating instructions(Operators and ConstantExprs). I am giving you directions to get started with understanding LLVM ...

June 18, 2019 - If agreed, some work will be needed to comply with these rules · Thanks for working on this, it's a seriously underspecified part of LLVM

August 4, 2019 - Followup on a recent discussion on D59978: It seems that the current consensus is that LLVM has a forward-progress requirement and also intends to keep it in the future. llvm.sideeffect is not a temporary workaround, but the final solution. While this is pretty disappointing for non-C++ frontends, ...

October 29, 2014 - Provide a full-fledged example of working variable arguments on X86_64, since it's easily the most popular platform. Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>

May 7, 2024 - No branching, and the hard part in FHE is to evaluate this when the bit is encrypted. The results are the same type, so all you see after the op is that the result is a ciphertext · Distributed Computing Through Combinatorial Topology: https://www.amazon.com/Distributed-Computing-Through-Combina

December 15, 2020 - This is a proposal for clarifying the semantics of lifetime.start / lifetime.end with @nlopes, @RalfJung. IIUC, the intrinsics are introduced to represent lifetimes of local variables while keeping allocas at the entry block in IR. However, their semantics was poorly described in LangRef · ...

Strided memrefs represent a view abstraction over preallocated data. They are constructed with special ops, yet to be introduced. Strided memrefs are a special subclass of memrefs with generic semi-affine map and correspond to a normalized memref descriptor when lowering to LLVM.

Oh and reading the LLVM langref it turns out llvm.fmuladd allows unfusion while llvm.fma will call libm if hardware FMA does not exist.

August 19, 2020 - LLVM IR currently assumes some form of forward progress. This form is not explicitly defined anywhere, and is the cause of miscompilations in most languages that are not C++11 or later. This implicit forward progress guarantee can not be opted out of on a function level nor on a loop level.