Ignore "no-frame-pointer-elim" and "no-frame-pointer-elim-non-leaf" in favor of "frame-pointer"

[MaskRay]

Summary

D56351 (included in LLVM 8.0.0) introduced "frame-pointer". All tests
which use "no-frame-pointer-elim" or "no-frame-pointer-elim-non-leaf"
have been migrated to use "frame-pointer".

Implement UpgradeFramePointerAttributes to upgrade the two obsoleted
function attributes for bitcode. Their semantics are ignored.

(I have patches to fix two downstream users: ldc and Julia (lightweight use in jit on Windows and FreeBSD)).

[MaskRay]

+ if (!F.hasFnAttribute("frame-pointer"))
+ return false;

(Forgot to include them..

[ychen]

Probably need to translate old attributes to new attribute in AutoUpgrade.cpp? Otherwise, this may cause problems for existing LTO libraries.

[rnk]

In D71863#1795794, @ychen wrote:

Probably need to translate old attributes to new attribute in AutoUpgrade.cpp? Otherwise, this may cause problems for existing LTO libraries.

+1, let's do that.

[MaskRay]

Implement UpgradeFramePointerAttributes to upgrade the two obsoleted function attributes for bitcode.

[ychen]

LGTM

llvm/docs/ReleaseNotes.rst

 * Windows Control Flow Guard: the ``-cfguard`` option now emits CFG checks on
   indirect function calls. The previous behavior is still available with the 
   ``-cfguard-nochecks`` option. Note that this feature should always be used 
   with optimizations enabled.
 
 * ``Callbacks`` have been added to ``CommandLine Options``.  These can
   be used to validate of selectively enable other options.
 
+* The function attributes ``no-frame-pointer-elim`` and
+  ``no-frame-pointer-elim-non-leaf`` have been replaced by ``frame-pointer``,
+  which has 3 values: ``none``, ``non-leaf``, and ``all``. The values mean what
+  functions must retain frame pointers.
+
 Changes to the LLVM IR
 ----------------------
 
 * Unnamed function arguments now get printed with their automatically
   generated name (e.g. "i32 %0") in definitions. This may require front-ends
   to update their tests; if so there is a script utils/add_argument_names.py
   that correctly converted 80-90% of Clang tests. Some manual work will almost
   certainly still be needed.

llvm/lib/CodeGen/TargetOptionsImpl.cpp

 /// optimization should be disabled for the given machine function.
 bool TargetOptions::DisableFramePointerElim(const MachineFunction &MF) const {
   // Check to see if the target want to forcably keep frame pointer.
   if (MF.getSubtarget().getFrameLowering()->keepFramePointer(MF))
     return true;
 
   const Function &F = MF.getFunction();
 
-  // TODO: Remove support for old `fp elim` function attributes after fully
-  //       migrate to use "frame-pointer"
-  if (!F.hasFnAttribute("frame-pointer")) {
-    // Check to see if we should eliminate all frame pointers.
-    if (F.getFnAttribute("no-frame-pointer-elim").getValueAsString() == "true")
-      return true;
-
-    // Check to see if we should eliminate non-leaf frame pointers.
-    if (F.hasFnAttribute("no-frame-pointer-elim-non-leaf"))
-      return MF.getFrameInfo().hasCalls();
-
+  if (!F.hasFnAttribute("frame-pointer"))
     return false;
-  }
-
   StringRef FP = F.getFnAttribute("frame-pointer").getValueAsString();
   if (FP == "all")
     return true;
   if (FP == "non-leaf")
     return MF.getFrameInfo().hasCalls();
   if (FP == "none")
     return false;
   llvm_unreachable("unknown frame pointer flag");
 }
 
 /// HonorSignDependentRoundingFPMath - Return true if the codegen must assume
 /// that the rounding mode of the FPU can change from its default.
 bool TargetOptions::HonorSignDependentRoundingFPMath() const {
   return !UnsafeFPMath && HonorSignDependentRoundingFPMathOption;
 }