[Hexagon] Handle returning small structures by value

This is compliant with the official ABI, but allows experimentation with
calling conventions.

llvm-svn: 275822

2 files changed, 25 insertions, 1 deletions

diff --git a/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp b/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
index 2a5d7d49be7..cdd4c2f8617 100644
--- a/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
+++ b/llvm/lib/Target/Hexagon/HexagonISelLowering.cpp
@@ -447,7 +447,13 @@ static bool RetCC_Hexagon32(unsigned ValNo, MVT ValVT,
                             MVT LocVT, CCValAssign::LocInfo LocInfo,
                             ISD::ArgFlagsTy ArgFlags, CCState &State) {
   if (LocVT == MVT::i32 || LocVT == MVT::f32) {
-    if (unsigned Reg = State.AllocateReg(Hexagon::R0)) {
+    // Note that use of registers beyond R1 is not ABI compliant. However there
+    // are (experimental) IR passes which generate internal functions that
+    // return structs using these additional registers.
+    static const uint16_t RegList[] = { Hexagon::R0, Hexagon::R1,
+                                        Hexagon::R2, Hexagon::R3,
+                                        Hexagon::R4, Hexagon::R5};
+    if (unsigned Reg = State.AllocateReg(RegList)) {
       State.addLoc(CCValAssign::getReg(ValNo, ValVT, Reg, LocVT, LocInfo));
       return false;
     }
diff --git a/llvm/test/CodeGen/Hexagon/ret-struct-by-val.ll b/llvm/test/CodeGen/Hexagon/ret-struct-by-val.ll
new file mode 100644
index 00000000000..26ed2ff36f7
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/ret-struct-by-val.ll
@@ -0,0 +1,18 @@
+; RUN: llc -march=hexagon < %s | FileCheck %s
+; CHECK: r0 = add(r0, r1)
+
+; Allow simple structures to be returned by value.
+
+%s = type { i32, i32 }
+
+declare %s @foo() #0
+
+define i32 @fred() #0 {
+  %t0 = call %s @foo()
+  %x = extractvalue %s %t0, 0
+  %y = extractvalue %s %t0, 1
+  %r = add i32 %x, %y
+  ret i32 %r
+}
+
+attributes #0 = { nounwind }