Add a Thumb readme entry.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75173 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/ARM/README-Thumb.txt b/lib/Target/ARM/README-Thumb.txt
index 4d3200b445c1298c6bd80006fb481844eee254f6..ecef58a32da3ad45f0e4422ba218baf205977629 100644 (file)
--- a/lib/Target/ARM/README-Thumb.txt
+++ b/lib/Target/ARM/README-Thumb.txt
@@ -226,3 +226,9 @@ etc. Almost all Thumb instructions clobber condition code.
 //===---------------------------------------------------------------------===//
 
 Add ldmia, stmia support.
+
+//===---------------------------------------------------------------------===//
+
+Thumb load / store address mode offsets are scaled. The values kept in the
+instruction operands are pre-scale values. This probably ought to be changed
+to avoid extra work when we convert Thumb2 instructions to Thumb1 instructions.