# Support for @simd for
module SimdLoop
export @simd
# Error thrown from ill-formed uses of @simd
type SimdError <: Exception
msg::ASCIIString
end
# Parse iteration space expression
# symbol '=' range
# symbol 'in' range
function parse_iteration_space(x)
(isa(x, Expr) && (x.head == :(=) || x.head == :in)) || throw(SimdError("= or in expected"))
length(x.args) == 2 || throw(SimdError("simd range syntax is wrong"))
isa(x.args[1], Symbol) || throw(SimdError("simd loop index must be a symbol"))
x.args # symbol, range
end
# reject invalid control flow statements in @simd loop body
function check_body!(x::Expr)
if x.head === :break || x.head == :continue
throw(SimdError("$(x.head) is not allowed inside a @simd loop body"))
elseif x.head === :macrocall && x.args[1] === symbol("@goto")
throw(SimdError("$(x.args[1]) is not allowed inside a @simd loop body"))
end
for arg in x.args
check_body!(arg)
end
return true
end
check_body!(x::QuoteNode) = check_body!(x.value)
check_body!(x) = true
# Compile Expr x in context of @simd.
function compile(x)
(isa(x, Expr) && x.head == :for) || throw(SimdError("for loop expected"))
length(x.args) == 2 || throw(SimdError("1D for loop expected"))
check_body!(x)
var,range = parse_iteration_space(x.args[1])
r = gensym("r") # Range value
n = gensym("n") # Trip count
i = gensym("i") # Trip index
quote
# Evaluate range value once, to enhance type and data flow analysis by optimizers.
let $r = $range, $n = length($r)
if zero($n) < $n
# Lower loop in way that seems to work best for LLVM 3.3 vectorizer.
let $i = zero($n)
while $i < $n
local $var = first($r) + $i*step($r)
$(x.args[2]) # Body of loop
$i += 1
$(Expr(:simdloop)) # Mark loop as SIMD loop
end
end
# Set index to last value just like a regular for loop would
$var = last($r)
end
end
nothing
end
end
macro simd(forloop)
esc(compile(forloop))
end
end # module SimdLoop