Add fastmath flag to PTXCompilerTarget (#492)

src/ptx.jl

@@ -18,6 +18,8 @@ Base.@kwdef struct PTXCompilerTarget <: AbstractCompilerTarget
     blocks_per_sm::Union{Nothing,Int} = nothing
     maxregs::Union{Nothing,Int} = nothing
 
+    fastmath::Bool = Base.JLOptions().fast_math == 1
+
     # deprecated; remove with next major version
     exitable::Union{Nothing,Bool} = nothing
     unreachable::Union{Nothing,Bool} = nothing
@@ -33,6 +35,7 @@ function Base.hash(target::PTXCompilerTarget, h::UInt)
     h = hash(target.maxthreads, h)
     h = hash(target.blocks_per_sm, h)
     h = hash(target.maxregs, h)
+    h = hash(target.fastmath, h)
 
     h
 end
@@ -82,6 +85,7 @@ function Base.show(io::IO, @nospecialize(job::CompilerJob{PTXCompilerTarget}))
     job.config.target.maxthreads !== nothing && print(io, ", maxthreads=$(job.config.target.maxthreads)")
     job.config.target.blocks_per_sm !== nothing && print(io, ", blocks_per_sm=$(job.config.target.blocks_per_sm)")
     job.config.target.maxregs !== nothing && print(io, ", maxregs=$(job.config.target.maxregs)")
+    job.config.target.fastmath && print(io, ", fast math enabled")
 end
 
 const ptx_intrinsics = ("vprintf", "__assertfail", "malloc", "free")
@@ -424,7 +428,7 @@ function nvvm_reflect!(fun::LLVM.Function)
         # handle possible cases
         # XXX: put some of these property in the compiler job?
         #      and/or first set the "nvvm-reflect-*" module flag like Clang does?
-        fast_math = Base.JLOptions().fast_math == 1
+        fast_math = current_job.config.target.fastmath
         # NOTE: we follow nvcc's --use_fast_math
         reflect_val = if reflect_arg == "__CUDA_FTZ"
             # single-precision denormals support
@@ -433,7 +437,7 @@ function nvvm_reflect!(fun::LLVM.Function)
             # single-precision floating-point division and reciprocals.
             ConstantInt(reflect_typ, fast_math ? 0 : 1)
         elseif reflect_arg == "__CUDA_PREC_SQRT"
-            # single-precision denormals support
+            # single-precision floating point square roots.
             ConstantInt(reflect_typ, fast_math ? 0 : 1)
         elseif reflect_arg == "__CUDA_FMAD"
             # contraction of floating-point multiplies and adds/subtracts into