Add explanatory comment.
llvm-svn: 138042
diff --git a/llvm/lib/Target/ARM/ARMInstrThumb.td b/llvm/lib/Target/ARM/ARMInstrThumb.td
index 199691f..a6e0ed7 100644
--- a/llvm/lib/Target/ARM/ARMInstrThumb.td
+++ b/llvm/lib/Target/ARM/ARMInstrThumb.td
@@ -125,6 +125,11 @@
// t_addrmode_rrs := reg + reg
//
+// We use separate scaled versions because the Select* functions need
+// to explicitly check for a matching constant and return false here so that
+// the reg+imm forms will match instead. This is a horrible way to do that,
+// as it forces tight coupling between the methods, but it's how selectiondag
+// currently works.
def t_addrmode_rrs1 : Operand<i32>,
ComplexPattern<i32, 2, "SelectThumbAddrModeRI5S1", []> {
let EncoderMethod = "getThumbAddrModeRegRegOpValue";
