Add more info to FIXME.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134729 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 8cd9aa2..d9bb3e6 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -1637,7 +1637,11 @@
return false;
// FIXME: Completely disable sibcall for Thumb1 since Thumb1RegisterInfo::
- // emitEpilogue is not ready for them.
+ // emitEpilogue is not ready for them. Thumb tail calls also use t2B, as
+ // the Thumb1 16-bit unconditional branch doesn't have sufficient relocation
+ // support in the assembler and linker to be used. This would need to be
+ // fixed to fully support tail calls in Thumb1.
+ //
// Doing this is tricky, since the LDM/POP instruction on Thumb doesn't take
// LR. This means if we need to reload LR, it takes an extra instructions,
// which outweighs the value of the tail call; but here we don't know yet