add loop pragmas

Author: vchuravy

base/Base.jl

@@ -347,6 +347,9 @@ include("util.jl")
 
 include("asyncmap.jl")
 
+# various loop pragmas
+include("pragmas.jl")
+
 # deprecated functions
 include("deprecated.jl")
 

base/pragma.jl

@@ -0,0 +1,93 @@
+module Pragma
+
+export @unroll
+
+##
+# Uses the loopinfo expr node to attach LLVM loopinfo to loops
+# the full list of supported metadata nodes is available at
+# https://llvm.org/docs/LangRef.html#llvm-loop
+# TODO:
+#   - Figure out how to deal with compile-time constants in `@unroll(N, expr)`
+#     so constants that come from `Val{N}` but are not parse time constant.
+#   - Difference between `unroll_enable` and `unroll_full`
+#   - ? Expose `unroll_disable`
+#   - ? Expose `jam_disable`
+##
+
+module MD
+    disable_nonforced() = (Symbol("llvm.loop.disable_nonforced"),)
+    interleave(n) = (Symbol("llvm.loop.interleave.count"), convert(Int, n))
+    vectorize_enable(flag) = (Symbol("llvm.loop.vectorize.enable"), convert(Bool, flag))
+    vectorize_width(n) = (Symbol("llvm.loop.vectorize.width"), convert(Int, n))
+    # ‘llvm.loop.vectorize.followup_vectorized’
+    # ‘llvm.loop.vectorize.followup_epilogue’
+    # ‘llvm.loop.vectorize.followup_all’
+    unroll_count(n) = (Symbol("llvm.loop.unroll.count"), convert(Int, n))
+    unroll_disable() = (Symbol("llvm.loop.unroll.disable"),)
+    unroll_enable() = (Symbol("llvm.loop.unroll.enable"),)
+    unroll_full() = (Symbol("llvm.loop.unroll.full"),)
+    # ‘llvm.loop.unroll.followup’
+    # ‘llvm.loop.unroll.followup_remainder’
+    jam_count(n) = (Symbol("llvm.loop.unroll_and_jam.count"), convert(Int, n))
+    jam_disable() = (Symbol("llvm.loop.unroll_and_jam.disable"),)
+    jam_enable() = (Symbol("llvm.loop.unroll_and_jam.enable"),)
+    # ‘llvm.loop.unroll_and_jam.followup_outer’
+    # ‘llvm.loop.unroll_and_jam.followup_inner’
+    # ‘llvm.loop.unroll_and_jam.followup_remainder_outer’
+    # ‘llvm.loop.unroll_and_jam.followup_remainder_inner’
+    # ‘llvm.loop.unroll_and_jam.followup_all’
+    # ‘llvm.loop.licm_versioning.disable’
+    # ‘llvm.loop.distribute.enable’
+    # ‘llvm.loop.distribute.followup_coincident’
+    # ‘llvm.loop.distribute.followup_sequential’
+    # ‘llvm.loop.distribute.followup_fallback’
+    # ‘llvm.loop.distribute.followup_all’
+end
+
+function loopinfo(name, expr, nodes...)
+    if expr.head != :for
+        error("Syntax error: pragma $name needs a for loop")
+    end
+    push!(expr.args[2].args, Expr(:loopinfo, nodes...))
+    return expr
+end
+
+"""
+   @unroll expr
+
+Takes a for loop as `expr` and informs the LLVM unroller to fully unroll it, if
+it is safe to do so and the loop count is known.
+"""
+macro unroll(expr)
+    expr = loopinfo("@unroll", expr, MD.unroll_full())
+    return esc(expr)
+end
+
+"""
+    @unroll N expr
+
+Takes a for loop as `expr` and informs the LLVM unroller to unroll it `N` times,
+if it is safe to do so.
+"""
+macro unroll(N, expr)
+    if !(N isa Integer)
+        error("Syntax error: `@unroll N expr` needs a constant integer N")
+    end
+    expr = loopinfo("@unroll", expr, MD.unroll_count(N))
+    return esc(expr)
+end
+
+macro jam(N, expr)
+    if !(N isa Integer)
+        error("Syntax error: `@jam N expr` needs a constant integer N")
+    end
+    expr = loopinfo("@jam", expr, MD.jam_count(N))
+    return esc(expr)
+end
+
+macro jam(expr)
+    expr = loopinfo("@jam", expr, MD.jam_enable())
+    return esc(expr)
+end
+
+end #module