Improve comments for r211040

Added comment to clarify why we r211040 choose to bail out of fast isel instead
of generating a more complicated relocation, and fix mislabelled register in the
comments of the asan test case.

llvm-svn: 211052

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86FastISel.cpp b/llvm/lib/Target/X86/X86FastISel.cpp
index 4b8a8362c5a..e490c274b5f 100644
--- a/llvm/lib/Target/X86/X86FastISel.cpp
+++ b/llvm/lib/Target/X86/X86FastISel.cpp
@@ -2709,7 +2709,10 @@ unsigned X86FastISel::TargetMaterializeConstant(const Constant *C) {
 
   // Materialize addresses with LEA instructions.
   if (isa<GlobalValue>(C)) {
-    //LEA can only handle 32 bit immediates
+    // LEA can only handle 32 bit immediates. Currently this happens pretty
+    // rarely, so rather than deal with it just bail out of fast isel. If any
+    // architectures endis up needing to use this path a lot then fast isel
+    // could get the address with a MOV64ri and use that to load the value.
     if (TM.getRelocationModel() == Reloc::Static && Subtarget->is64Bit())
       return false;