Implements the @nonans decorator to enable some LLVM vectorizations

base/essentials.jl

@@ -113,6 +113,11 @@ macro _propagate_inbounds_meta()
     return Expr(:meta, :inline, :propagate_inbounds)
 end
 
+# Alternative to `@nonans`.
+macro _nonans_meta()
+    return Expr(:meta, :nonans)
+end
+
 """
     convert(T, x)
 

base/exports.jl

@@ -971,6 +971,7 @@ export
     @nospecialize,
     @specialize,
     @polly,
+    @nonans,
 
     @assert,
     @__dot__,

base/expr.jl

@@ -256,6 +256,23 @@ macro polly(ex)
     esc(isa(ex, Expr) ? pushmeta!(ex, :polly) : ex)
 end
 
+"""
+    @nonans
+
+Allows the compiler to assume no NaNs on floating-point operations.
+
+```julia
+@nonans function mathfunc(x)
+    #=
+        Function Definition
+    =#
+end
+```
+"""
+macro nonans(ex)
+    esc(isa(ex, Expr) ? pushmeta!(ex, :nonans) : ex)
+end
+
 ## some macro utilities ##
 
 function pushmeta!(ex::Expr, sym::Symbol, args::Any...)

src/ast.c

@@ -62,6 +62,7 @@ jl_sym_t *throw_undef_if_not_sym; jl_sym_t *getfield_undefref_sym;
 jl_sym_t *gc_preserve_begin_sym; jl_sym_t *gc_preserve_end_sym;
 jl_sym_t *escape_sym;
 jl_sym_t *aliasscope_sym; jl_sym_t *popaliasscope_sym;
+jl_sym_t *nonans_sym;
 
 static uint8_t flisp_system_image[] = {
 #include <julia_flisp.boot.inc>
@@ -367,6 +368,7 @@ void jl_init_frontend(void)
     do_sym = jl_symbol("do");
     aliasscope_sym = jl_symbol("aliasscope");
     popaliasscope_sym = jl_symbol("popaliasscope");
+    nonans_sym = jl_symbol("nonans");
 }
 
 JL_DLLEXPORT void jl_lisp_prompt(void)

src/codegen.cpp

@@ -5618,6 +5618,10 @@ static std::unique_ptr<Module> emit_function(
         f->addFnAttr(Attribute::NoInline);
     }
 
+    if (jl_has_meta(stmts, nonans_sym)) {
+        f->addFnAttr("no-nans-fp-math", "true");
+    }
+
     if (returninfo.cc == jl_returninfo_t::Union) {
         f->addAttribute(1, Attribute::getWithDereferenceableBytes(jl_LLVMContext, returninfo.union_bytes));
         f->addAttribute(1, Attribute::getWithAlignment(jl_LLVMContext, returninfo.union_align));

src/julia_internal.h

@@ -1053,6 +1053,7 @@ extern jl_sym_t *throw_undef_if_not_sym; extern jl_sym_t *getfield_undefref_sym;
 extern jl_sym_t *gc_preserve_begin_sym; extern jl_sym_t *gc_preserve_end_sym;
 extern jl_sym_t *failed_sym; extern jl_sym_t *done_sym; extern jl_sym_t *runnable_sym;
 extern jl_sym_t *escape_sym;
+extern jl_sym_t *nonans_sym;
 
 struct _jl_sysimg_fptrs_t;
 

test/llvmpasses/nonans.jl

@@ -0,0 +1,21 @@
+# This file is a part of Julia. License is MIT: https://julialang.org/license
+
+# RUN: julia --startup-file=no %s %t && llvm-link -S %t/* -o %t/module.ll
+# RUN: cat %t/module.ll | FileCheck %s
+
+## Notes:
+# This script uses the `emit` function (defined llvmpasses.jl) to emit either
+# optimized or unoptimized LLVM IR. Each function is emitted individually and
+# `llvm-link` is used to create a single module that can be passed to opt.
+# The order in which files are emitted and linked is important since `lit` will
+# process the test cases in order.
+
+include(joinpath("..", "testhelpers", "llvmpasses.jl"))
+
+# CHECK-LABEL: @julia_minimum_nonans
+@nonans function minimum_nonans(itr)
+    return reduce(itr) do a, b ifelse(a < b, a, b) end
+end
+
+# CHECK: attributes #{{[0-9]+}} = {{{[a-z "=]*}}"no-nans-fp-math"="true"{{[a-z "=]*}}}
+emit(minimum_nonans, Vector{Float64})