Simple test functions generates different codegen

[mmh]

I would have that thought that these two function would produce the same code, but they do not.

Could someone care to explain the difference and which is preferred and why

http://pastebin.com/GJ8YPfV3

function test1(x)

y = 2.0

u = 2.320

x < 0 && (u = 32.0)

x > 1 && (u = 1.0)

return u + y

end

function test2(x)

y = 2.0

u = 2.320

u = x < 0 ? 32.0 : u

u = x > 1 ? 1.0 : u

return u + y

end

@code_llvm test1(2.2)

@code_llvm test2(2.2)

[Isaiah Norton]

These expressions are lowered differently because `test2` gets a temporary due to the conditional reassignment of `u`, whereas `test1` is just a straight line switch and jump (look at `code_lowered` and `code_typed`).

For the same C code, the lowered IR from Clang looks similar, but it appears to constant fold and reduce down to identical assembly at `-O1` and above. The fact that Julia doesn't is probably due to difference in LLVM optimization passes or order.

As far as style, personally I think the first one is cleaner.

[mmh]

Ah right, I forgot @code_lowered even existed , thanks for that. Yeah gcc/clang all have the same native code from this snippet, which is why I was surprised that the same julia code was produced different  code native.  

[Stefan Karpinski]

Julia has to do a delicate balancing act between compilation speed and runtime speed. In the future, we may introduce multiple compilation tiers as many other JITs have, but so far we've managed to avoid it, which is really actually quite nice for both keeping implementation complexity down and for performance being predictable. Ideally we can figure out other ways to make compilation faster without compiler tiers.