From 7a9970f02e8a873ee4ea5f7c09d62d1203a4dd22 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Tue, 27 Nov 2018 06:34:44 -0500
Subject: [PATCH] Update comments and cpu feature test

---
 TestPrograms/test_ppc_power9.cxx | 31 +++++++++++++++++--------------
 darn.h                           | 10 +++++-----
 2 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/TestPrograms/test_ppc_power9.cxx b/TestPrograms/test_ppc_power9.cxx
index 82e1e755..38e87398 100644
--- a/TestPrograms/test_ppc_power9.cxx
+++ b/TestPrograms/test_ppc_power9.cxx
@@ -1,6 +1,20 @@
+// The problem we have here is, it appears only GCC 7.0 and above
+// support Power9 builtins. Clang 7.0 has support for some (all?)
+// assembly instructions but we don't see builtin support. We can't
+// determine the state of XLC. Searching IBM's website for
+// terms like 'darn' 'random number' is returning irrelevant hits.
+// Searching with Google from the outside returns 0 hits.
+//
+// The support disconnect means we may report Power9 as unavailable
+// and support DARN at the same time. We get into that state because
+// we use inline asm to detect DARN availablity in the compiler.
+// Also see cpu.cpp and the two query functions; and ppc_power9.cpp
+// and the two probe functions.
+
 #include <altivec.h>
 int main(int argc, char* argv[])
 {
+#if 0
 	const unsigned char b = (unsigned char)argc;
 	const unsigned int r = (0xf << 24) | (0x3 << 16) | (0xf << 8) | (0x3 << 0);
 #if defined(__clang__)
@@ -10,23 +24,12 @@ int main(int argc, char* argv[])
 #else
 	int XXX[-1];
 #endif
+#endif
 
-#if UINTPTR_MAX == 0xffffffffffffffffULL
-#  if defined(__clang__)
-	unsigned long long y = __builtin_altivec_darn();
-#  elif defined(__GNUC__)
-	unsigned long long y = __builtin_darn();
-#  else
-	int XXX[-1];
-#  endif
-#else
-#  if defined(__clang__)
-	unsigned int y = __builtin_altivec_darn_32();
-#  elif defined(__GNUC__)
+#if defined(__GNUC__) || defined(__IBM_GCC_ASM)
 	unsigned int y = __builtin_darn_32();
-#  else
+#else
 	int XXX[-1];
-#  endif
 #endif
 
 	return 0;
diff --git a/darn.h b/darn.h
index 613a9b0d..c56e07b6 100644
--- a/darn.h
+++ b/darn.h
@@ -2,11 +2,11 @@
 //          DARN requires POWER9/ISA 3.0.
 
 // At the moment only GCC 7.0 (and above) seems to support __builtin_darn()
-// and __builtin_darn_32(). Clang 7.0 does not provide them. XLC is unknown,
-// but there are no hits when searching IBM's site. To cover more platforms
-// we provide GCC inline assembly like we do with RDRAND and RDSEED.
-// Platforms that don't support GCC inline assembly or the builtin will fail
-// the compile. Also see
+// and __builtin_darn_32(). Clang 7.0 does not provide them, but it does
+// support assembly instructions. XLC is unknown, but there are no hits when
+// searching IBM's site. To cover more platforms we provide GCC inline
+// assembly like we do with RDRAND and RDSEED. Platforms that don't support
+// GCC inline assembly or the builtin will fail the compile. Also see
 // https://gcc.gnu.org/onlinedocs/gcc/Basic-PowerPC-Built-in-Functions-Available-on-ISA-3_002e0.html
 
 /// \file darn.h