TableGen: Reimplement !foreach using the resolving mechanism

Summary:
This changes the syntax of !foreach so that the first "parameter" is
a new syntactic variable: !foreach(x, lst, expr) will define the
variable x within the scope of expr, and evaluation of the !foreach
will substitute elements of the given list (or dag) for x in expr.

Aside from leading to a nicer syntax, this allows more complex
expressions where x is deeply nested, or even constant expressions
in which x does not occur at all.

!foreach is currently not actually used anywhere in trunk, but I
plan to use it in the AMDGPU backend. If out-of-tree targets are
using it, they can adjust to the new syntax very easily.

Change-Id: Ib966694d8ab6542279d6bc358b6f4d767945a805

Reviewers: arsenm, craig.topper, tra, MartinO

Subscribers: wdng, llvm-commits, tpr

Differential Revision: https://reviews.llvm.org/D43651

llvm-svn: 326705

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/docs/TableGen/LangIntro.rst b/llvm/docs/TableGen/LangIntro.rst
index 534597b041b..69e5c1426e4 100644
--- a/llvm/docs/TableGen/LangIntro.rst
+++ b/llvm/docs/TableGen/LangIntro.rst
@@ -192,9 +192,9 @@ supported include:
     for 'a' in 'c.'  This operation is analogous to $(subst) in GNU make.
 
 ``!foreach(a, b, c)``
-    For each member of dag or list 'b' apply operator 'c.'  'a' is a dummy
-    variable that should be declared as a member variable of an instantiated
-    class.  This operation is analogous to $(foreach) in GNU make.
+    For each member of dag or list 'b' apply operator 'c'. 'a' is the name
+    of a variable that will be substituted by members of 'b' in 'c'.
+    This operation is analogous to $(foreach) in GNU make.
 
 ``!head(a)``
     The first element of list 'a.'