Added some notes on the -triple and -arch options.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@44554 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/NOTES.txt b/NOTES.txt
index ea7d206..1266718 100644
--- a/NOTES.txt
+++ b/NOTES.txt
@@ -120,6 +120,47 @@
allowing a single index to be used for all fat slices.
//===---------------------------------------------------------------------===//
+// Specifying targets: -triple and -arch
+===---------------------------------------------------------------------===//
+
+The clang supports "-triple" and "-arch" options. At most one -triple option may
+be specified, while multiple -arch options can be specified. Both are optional.
+
+The "selection of target" behavior is defined as follows:
+
+(1) If the user does not specify -triple:
+
+ (a) If no -arch options are specified, the target triple used is the host
+ triple (in llvm/Config/config.h).
+
+ (b) If one or more -arch's are specified (and no -triple), then there is
+ one triple for each -arch, where the specified arch is substituted
+ for the arch in the host triple. Example:
+
+ host triple = i686-apple-darwin9
+ command: clang -arch ppc -arch ppc64 ...
+ triples used: ppc-apple-darwin9 ppc64-apple-darwin9
+
+(2) The user does specify a -triple (only one allowed):
+
+ (a) If no -arch options are specified, the triple specified by -triple
+ is used. E.g clang -triple i686-apple-darwin9
+
+ (b) If one or more -arch options are specified, then the triple specified
+ by -triple is used as the primary target, and the arch's specified
+ by -arch are used to create secondary targets. For example:
+
+ clang -triple i686-apple-darwin9 -arch ppc -arch ppc64
+
+ has the following targets:
+
+ i686-apple-darwin9 (primary target)
+ ppc-apple-darwin9 (secondary target)
+ ppc64-apple-darwin9 (secondary target)
+
+The secondary targets are used in the 'portability' model (see below).
+
+//===---------------------------------------------------------------------===//
The 'portability' model in clang is sufficient to catch translation units (or
their parts) that are not portable, but it doesn't help if the system headers