[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.

8 files changed, 39 insertions, 14 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");
   }
diff --git a/llvm/lib/CodeGen/TargetOptionsImpl.cpp b/llvm/lib/CodeGen/TargetOptionsImpl.cpp
index af5d101..5bf1d26 100644
--- a/llvm/lib/CodeGen/TargetOptionsImpl.cpp
+++ b/llvm/lib/CodeGen/TargetOptionsImpl.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/TargetFrameLowering.h"
@@ -21,7 +22,7 @@ using namespace llvm;
 /// DisableFramePointerElim - This returns true if frame pointer elimination
 /// 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.
+  // Check to see if the target want to forcibly keep frame pointer.
   if (MF.getSubtarget().getFrameLowering()->keepFramePointer(MF))
     return true;
 
@@ -34,11 +35,27 @@ bool TargetOptions::DisableFramePointerElim(const MachineFunction &MF) const {
     return true;
   if (FP == "non-leaf")
     return MF.getFrameInfo().hasCalls();
-  if (FP == "none")
+  if (FP == "none" || FP == "reserved")
     return false;
   llvm_unreachable("unknown frame pointer flag");
 }
 
+bool TargetOptions::FramePointerIsReserved(const MachineFunction &MF) const {
+  // Check to see if the target want to forcibly keep frame pointer.
+  if (MF.getSubtarget().getFrameLowering()->keepFramePointer(MF))
+    return true;
+
+  const Function &F = MF.getFunction();
+
+  if (!F.hasFnAttribute("frame-pointer"))
+    return false;
+
+  StringRef FP = F.getFnAttribute("frame-pointer").getValueAsString();
+  return StringSwitch<bool>(FP)
+      .Cases("all", "non-leaf", "reserved", true)
+      .Case("none", false);
+}
+
 /// HonorSignDependentRoundingFPMath - Return true if the codegen must assume
 /// that the rounding mode of the FPU can change from its default.
 bool TargetOptions::HonorSignDependentRoundingFPMath() const {
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index 13fa1af..3f73502 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -383,6 +383,9 @@ Function *Function::createWithDefaultAttr(FunctionType *Ty,
   case FramePointerKind::None:
     // 0 ("none") is the default.
     break;
+  case FramePointerKind::Reserved:
+    B.addAttribute("frame-pointer", "reserved");
+    break;
   case FramePointerKind::NonLeaf:
     B.addAttribute("frame-pointer", "non-leaf");
     break;
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 684e544..e592720 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -2322,7 +2322,7 @@ void Verifier::verifyFunctionAttrs(FunctionType *FT, AttributeList Attrs,
 
   if (Attrs.hasFnAttr("frame-pointer")) {
     StringRef FP = Attrs.getFnAttr("frame-pointer").getValueAsString();
-    if (FP != "all" && FP != "non-leaf" && FP != "none")
+    if (FP != "all" && FP != "non-leaf" && FP != "none" && FP != "reserved")
       CheckFailed("invalid value for 'frame-pointer' attribute: " + FP, V);
   }
 
diff --git a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index 9adf758..c149db31 100644
--- a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -207,7 +207,7 @@ getReservedRegs(const MachineFunction &MF) const {
   markSuperRegs(Reserved, ARM::PC);
   markSuperRegs(Reserved, ARM::FPSCR);
   markSuperRegs(Reserved, ARM::APSR_NZCV);
-  if (TFI->hasFP(MF))
+  if (TFI->isFPReserved(MF))
     markSuperRegs(Reserved, STI.getFramePointerReg());
   if (hasBasePointer(MF))
     markSuperRegs(Reserved, BasePtr);
diff --git a/llvm/lib/Target/ARM/ARMFeatures.td b/llvm/lib/Target/ARM/ARMFeatures.td
index 84481af..8b0ade5 100644
--- a/llvm/lib/Target/ARM/ARMFeatures.td
+++ b/llvm/lib/Target/ARM/ARMFeatures.td
@@ -548,16 +548,15 @@ def FeatureFixCortexA57AES1742098 : SubtargetFeature<"fix-cortex-a57-aes-1742098
   "FixCortexA57AES1742098", "true",
   "Work around Cortex-A57 Erratum 1742098 / Cortex-A72 Erratum 1655431 (AES)">;
 
+// If frame pointers are in use, they must follow the AAPCS definition, which
+// always uses R11 as the frame pointer. If this is not set, we can use R7 as
+// the frame pointer for Thumb1-only code, which is more efficient, but less
+// compatible. Note that this feature does not control whether frame pointers
+// are emitted, that is controlled by the "frame-pointer" function attribute.
 def FeatureAAPCSFrameChain : SubtargetFeature<"aapcs-frame-chain",
                                               "CreateAAPCSFrameChain", "true",
                                               "Create an AAPCS compliant frame chain">;
 
-def FeatureAAPCSFrameChainLeaf : SubtargetFeature<"aapcs-frame-chain-leaf",
-                                                  "CreateAAPCSFrameChainLeaf", "true",
-                                                  "Create an AAPCS compliant frame chain "
-                                                  "for leaf functions",
-                                                  [FeatureAAPCSFrameChain]>;
-
 // Assume that lock-free 32-bit atomics are available, even if the target
 // and operating system combination would not usually provide them. The user
 // is responsible for providing any necessary __sync implementations. Code
diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index 11496a6..831b6b0 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
@@ -215,7 +215,7 @@ bool ARMFrameLowering::hasFP(const MachineFunction &MF) const {
 /// isFPReserved - Return true if the frame pointer register should be
 /// considered a reserved register on the scope of the specified function.
 bool ARMFrameLowering::isFPReserved(const MachineFunction &MF) const {
-  return hasFP(MF) || MF.getSubtarget<ARMSubtarget>().createAAPCSFrameChain();
+  return hasFP(MF) || MF.getTarget().Options.FramePointerIsReserved(MF);
 }
 
 /// hasReservedCallFrame - Under normal circumstances, when a frame pointer is
@@ -2233,10 +2233,10 @@ bool ARMFrameLowering::enableShrinkWrapping(const MachineFunction &MF) const {
   return true;
 }
 
-static bool requiresAAPCSFrameRecord(const MachineFunction &MF) {
+bool ARMFrameLowering::requiresAAPCSFrameRecord(
+    const MachineFunction &MF) const {
   const auto &Subtarget = MF.getSubtarget<ARMSubtarget>();
-  return Subtarget.createAAPCSFrameChainLeaf() ||
-         (Subtarget.createAAPCSFrameChain() && MF.getFrameInfo().hasCalls());
+  return Subtarget.createAAPCSFrameChain() && hasFP(MF);
 }
 
 // Thumb1 may require a spill when storing to a frame index through FP (or any
diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.h b/llvm/lib/Target/ARM/ARMFrameLowering.h
index 3c7358d..6a31b73 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.h
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.h
@@ -47,6 +47,7 @@ public:
 
   bool hasFP(const MachineFunction &MF) const override;
   bool isFPReserved(const MachineFunction &MF) const;
+  bool requiresAAPCSFrameRecord(const MachineFunction &MF) const;
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
   bool canSimplifyCallFramePseudos(const MachineFunction &MF) const override;
   StackOffset getFrameIndexReference(const MachineFunction &MF, int FI,