[ARM] r11 is reserved when using -mframe-chain=aapcs (#86951)

When using the -mframe-chain=aapcs or -mframe-chain=aapcs-leaf options,
we cannot use r11 as an allocatable register, even if
-fomit-frame-pointer is also used. This is so that r11 will always point
to a valid frame record, even if we don't create one in every function.

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CommandFlags.cpp b/llvm/lib/CodeGen/CommandFlags.cpp
index 677460a..8fc65d7 100644
--- a/llvm/lib/CodeGen/CommandFlags.cpp
+++ b/llvm/lib/CodeGen/CommandFlags.cpp
@@ -211,6 +211,9 @@ codegen::RegisterCodeGenFlags::RegisterCodeGenFlags() {
                      "Disable frame pointer elimination"),
           clEnumValN(FramePointerKind::NonLeaf, "non-leaf",
                      "Disable frame pointer elimination for non-leaf frame"),
+          clEnumValN(FramePointerKind::Reserved, "reserved",
+                     "Enable frame pointer elimination, but reserve the frame "
+                     "pointer register"),
           clEnumValN(FramePointerKind::None, "none",
                      "Enable frame pointer elimination")));
   CGBINDOPT(FramePointerUsage);
@@ -693,6 +696,8 @@ void codegen::setFunctionAttributes(StringRef CPU, StringRef Features,
       NewAttrs.addAttribute("frame-pointer", "all");
     else if (getFramePointerUsage() == FramePointerKind::NonLeaf)
       NewAttrs.addAttribute("frame-pointer", "non-leaf");
+    else if (getFramePointerUsage() == FramePointerKind::Reserved)
+      NewAttrs.addAttribute("frame-pointer", "reserved");
     else if (getFramePointerUsage() == FramePointerKind::None)
       NewAttrs.addAttribute("frame-pointer", "none");
   }