LLVM evaluation

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1

Hi,

My organization is doing a technology comparison between GCC
optimization/backend and LLVM infrastructures to select the best
environment for our next product. Would you please help me to find
answers on the following features’ list support availability inside
current (or near future) LLVM implementation:

1. Intrinsic function support
2. Semi-standard embedded C types (complex, fractional) support
3. Target specific built-in types support (like 48-bit integrals)
4. Types similar to GCC vectorization types
5. Overlapped register classes support (same instructions, but working
inside different execution units on separate registers set)
6. Peephole optimization that works on non-sequential instructions (in
contrast to GCC’s peephole)
7. Parallelism (explicit instruction bundling) for VLIW architectures
8. Delay slots support
9. Software pipelining
10. Quality of alias analysis
11. Registers renaming optimization
12. Speculative scheduling

It will be very helpful if you can help to find examples and/or
targets that can be served as references for each particular item.

Thank you,
Frank

2

Hi,

My organization is doing a technology comparison between GCC
optimization/backend and LLVM infrastructures to select the best
environment for our next product. Would you please help me to find
answers on the following features’ list support availability inside
current (or near future) LLVM implementation:

1. Intrinsic function support

http://llvm.org/docs/ExtendingLLVM.html#intrinsic

2. Semi-standard embedded C types (complex, fractional) support

In LLVM, front-ends must lower these to lower-level types. This is often
sufficient, though it impedes custom high-level optimizations.

3. Target specific built-in types support (like 48-bit integrals)

Somewhat. LLVM's midlevel optimizer type system can handle
non-power-of-two integer types. Support for non-power-of-two integer
types in the backend is limited to lowering them into power-of-two integer
types though.

4. Types similar to GCC vectorization types

http://llvm.org/docs/LangRef.html#t_vector

5. Overlapped register classes support (same instructions, but working
inside different execution units on separate registers set)

No. You can define separate instructions, but there's nothing to help select
between them. In particular, LLVM has nothing to compare with GCC's
multi-alternative constraints.

6. Peephole optimization that works on non-sequential instructions (in
contrast to GCC’s peephole)

"Peephole" is ambiguous here. LLVM can do simplifications on SSA graphs,
which are non-sequential. GCC can do this too. But perhaps you're thinking
of something more specific.

7. Parallelism (explicit instruction bundling) for VLIW architectures

No.

8. Delay slots support

You can look at what LLVM's MIPS and Sparc backends do.

9. Software pipelining

No.

10. Quality of alias analysis

http://llvm.org/docs/AliasAnalysis.html#exist

but note that -seens-aa and -ds-aa are not generally usable, and -scev-aa is
currently a curiosity.

11. Registers renaming optimization

Can you be more specific?

12. Speculative scheduling

No.

Dan