[CodeGen] Add thumb-mode to target-features for arm/thumb triples.

Summary:
The thumb-mode target feature is used to force Thumb or ARM code
generation on a per-function basis. Explicitly adding +thumb-mode to
functions for thumbxx triples enables mixed ARM/Thumb code generation in
places where compilation units with thumbxx and armxx triples are merged
together (e.g. the IR linker or LTO).

For armxx triples, -thumb-mode is added in a similar fashion.

Reviewers: echristo, t.p.northover, kristof.beyls, rengolin

Reviewed By: echristo

Subscribers: rinon, aemerson, mehdi_amini, javed.absar, cfe-commits

Differential Revision: https://reviews.llvm.org/D33448

llvm-svn: 304897

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Basic/Targets.cpp b/clang/lib/Basic/Targets.cpp
index a304a78354e..89f192abc07 100644
--- a/clang/lib/Basic/Targets.cpp
+++ b/clang/lib/Basic/Targets.cpp
@@ -5442,6 +5442,13 @@ public:
       if (Feature[0] == '+')
         Features[Feature.drop_front(1)] = true;
 
+    // Enable or disable thumb-mode explicitly per function to enable mixed
+    // ARM and Thumb code generation.
+    if (isThumb())
+      Features["thumb-mode"] = true;
+    else
+      Features["thumb-mode"] = false;
+
     // Convert user-provided arm and thumb GNU target attributes to
     // [-|+]thumb-mode target features respectively.
     std::vector<std::string> UpdatedFeaturesVec(FeaturesVec);