[PATCH] D85879: [OpenMP] Overload `std::isnan` and friends multiple times for the GPU

[Johannes Doerfert via Phabricator via cfe-commits]

jdoerfert created this revision.
jdoerfert added reviewers: JonChesterfield, jhuber6, ABataev, MaskRay.
Herald added subscribers: guansong, bollu, yaxunl.
Herald added a project: clang.
jdoerfert requested review of this revision.
Herald added a subscriber: sstefan1.

`std::isnan` and friends can be found in two variants in the wild, one
returns `bool`, as the standard defines it, one returns `int`, as the C
macros do. So far we kinda hoped the system versions of these functions
will work for people, e.g. they are definitions that can be compiled for
the target. We know that is not the case always so we leverage the
`disable_implicit_base` OpenMP context extension to specialize both
versions of these functions without causing an invalid redeclaration.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D85879

Files:
  clang/lib/Headers/__clang_cuda_cmath.h


Index: clang/lib/Headers/__clang_cuda_cmath.h
===================================================================
--- clang/lib/Headers/__clang_cuda_cmath.h
+++ clang/lib/Headers/__clang_cuda_cmath.h
@@ -66,10 +66,29 @@
 }
 
 // For inscrutable reasons, the CUDA headers define these functions for us on
-// Windows. For OpenMP we omit these as some old system headers have
-// non-conforming `isinf(float)` and `isnan(float)` implementations that return
-// an `int`. The system versions of these functions should be fine anyway.
+// Windows.
 #if !defined(_MSC_VER) && !defined(__OPENMP_NVPTX__)
+
+// For OpenMP we work around some old system headers that have non-conforming
+// `isinf(float)` and `isnan(float)` implementations that return an `int`. We do
+// this by providing two versions of these functions, differing only in the
+// return type. To avoid conflicting definitions we disable implicit base
+// function generation. That means we will end up with two specializations, one
+// per type, but only one has a base function defined by the system header.
+#if defined(__OPENMP_NVPTX__)
+#pragma omp begin declare variant match(                                       \
+    device = {arch(nvptx, nvptx64)},                                           \
+    implementation = {extension(disable_implicit_base)})
+
+__DEVICE__ int isinf(float __x) { return ::__isinff(__x); }
+__DEVICE__ int isinf(double __x) { return ::__isinf(__x); }
+__DEVICE__ int isfinite(float __x) { return ::__finitef(__x); }
+__DEVICE__ int isfinite(double __x) { return ::__isfinited(__x); }
+__DEVICE__ int isnan(float __x) { return ::__isnanf(__x); }
+__DEVICE__ int isnan(double __x) { return ::__isnan(__x); }
+
+#endif
+
 __DEVICE__ bool isinf(float __x) { return ::__isinff(__x); }
 __DEVICE__ bool isinf(double __x) { return ::__isinf(__x); }
 __DEVICE__ bool isfinite(float __x) { return ::__finitef(__x); }
@@ -79,6 +98,11 @@
 __DEVICE__ bool isfinite(double __x) { return ::__isfinited(__x); }
 __DEVICE__ bool isnan(float __x) { return ::__isnanf(__x); }
 __DEVICE__ bool isnan(double __x) { return ::__isnan(__x); }
+
+#if defined(__OPENMP_NVPTX__)
+#pragma omp end declare variant
+#endif
+
 #endif
 
 __DEVICE__ bool isgreater(float __x, float __y) {


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