void updated this revision to Diff 427909.
void added a comment.

- Support SVE registers.
- Initial feature to gather argument registers from the *CallingConv.td files.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124836/new/

https://reviews.llvm.org/D124836

Files:
  clang/include/clang/Driver/Options.td
  clang/lib/Driver/ToolChains/Clang.cpp
  llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
  llvm/lib/Target/AArch64/AArch64FrameLowering.h
  llvm/lib/Target/AArch64/AArch64RegisterInfo.td
  llvm/lib/Target/X86/X86RegisterInfo.cpp
  llvm/test/CodeGen/AArch64/zero-call-used-regs.ll
  llvm/utils/TableGen/CallingConvEmitter.cpp
  llvm/utils/TableGen/RegisterInfoEmitter.cpp

Index: llvm/utils/TableGen/RegisterInfoEmitter.cpp
===================================================================
--- llvm/utils/TableGen/RegisterInfoEmitter.cpp
+++ llvm/utils/TableGen/RegisterInfoEmitter.cpp
@@ -1188,6 +1188,8 @@
      << "MCRegister) const override;\n"
      << "  bool isFixedRegister(const MachineFunction &, "
      << "MCRegister) const override;\n"
+     << "  bool isArgumentRegister(const MachineFunction &, "
+     << "MCRegister) const override;\n"
      << "  /// Devirtualized TargetFrameLowering.\n"
      << "  static const " << TargetName << "FrameLowering *getFrameLowering(\n"
      << "      const MachineFunction &MF);\n"
@@ -1662,6 +1664,20 @@
   OS << "      false;\n";
   OS << "}\n\n";
 
+  OS << "bool " << ClassName << "::\n"
+     << "isArgumentRegister(const MachineFunction &MF, "
+     << "MCRegister PhysReg) const {\n"
+     << "  return\n";
+  for (const CodeGenRegisterCategory &Category : RegCategories)
+    if (Category.getName() == "ArgumentRegisters") {
+      for (const CodeGenRegisterClass *RC : Category.getClasses())
+        OS << "      " << RC->getQualifiedName()
+           << "RegClass.contains(PhysReg) ||\n";
+      break;
+    }
+  OS << "      false;\n";
+  OS << "}\n\n";
+
   OS << "ArrayRef<const char *> " << ClassName
      << "::getRegMaskNames() const {\n";
   if (!CSRSets.empty()) {
Index: llvm/utils/TableGen/CallingConvEmitter.cpp
===================================================================
--- llvm/utils/TableGen/CallingConvEmitter.cpp
+++ llvm/utils/TableGen/CallingConvEmitter.cpp
@@ -20,6 +20,13 @@
 namespace {
 class CallingConvEmitter {
   RecordKeeper &Records;
+  unsigned Counter;
+  std::string CurrentAction;
+  bool SwiftAction;
+
+  std::map<std::string, std::set<std::string>> AssignedRegsMap;
+  std::map<std::string, std::set<std::string>> AssignedSwiftRegsMap;
+  std::map<std::string, std::set<std::string>> DelegateToMap;
 public:
   explicit CallingConvEmitter(RecordKeeper &R) : Records(R) {}
 
@@ -28,7 +35,7 @@
 private:
   void EmitCallingConv(Record *CC, raw_ostream &O);
   void EmitAction(Record *Action, unsigned Indent, raw_ostream &O);
-  unsigned Counter;
+  void EmitArgRegisterLists(raw_ostream &O);
 };
 } // End anonymous namespace
 
@@ -58,18 +65,23 @@
   // Emit each non-custom calling convention description in full.
   Records.startTimer("Emit full descriptions");
   for (Record *CC : CCs) {
-    if (!CC->getValueAsBit("Custom"))
+    if (!CC->getValueAsBit("Custom")) {
+      // Call upon the creation of a map entry from the void!
+      CurrentAction = CC->getName().str();
+      (void)AssignedRegsMap[CurrentAction];
       EmitCallingConv(CC, O);
+    }
   }
-}
 
+  EmitArgRegisterLists(O);
+}
 
 void CallingConvEmitter::EmitCallingConv(Record *CC, raw_ostream &O) {
   ListInit *CCActions = CC->getValueAsListInit("Actions");
   Counter = 0;
 
   O << "\n\n";
-  unsigned Pad = CC->getName().size();
+  unsigned Pad = CurrentAction.size();
   if (CC->getValueAsBit("Entry")) {
     O << "bool llvm::";
     Pad += 12;
@@ -77,13 +89,21 @@
     O << "static bool ";
     Pad += 13;
   }
-  O << CC->getName() << "(unsigned ValNo, MVT ValVT,\n"
+  O << CurrentAction << "(unsigned ValNo, MVT ValVT,\n"
     << std::string(Pad, ' ') << "MVT LocVT, CCValAssign::LocInfo LocInfo,\n"
     << std::string(Pad, ' ') << "ISD::ArgFlagsTy ArgFlags, CCState &State) {\n";
   // Emit all of the actions, in order.
   for (unsigned i = 0, e = CCActions->size(); i != e; ++i) {
+    Record *Action = CCActions->getElementAsRecord(i);
+    SwiftAction =
+        llvm::any_of(Action->getSuperClasses(),
+                     [](const std::pair<Record *, SMRange> &Class) {
+                       std::string Name = Class.first->getNameInitAsString();
+                       return StringRef(Name).startswith("CCIfSwift");
+                     });
+
     O << "\n";
-    EmitAction(CCActions->getElementAsRecord(i), 2, O);
+    EmitAction(Action, 2, O);
   }
   
   O << "\n  return true; // CC didn't match.\n";
@@ -93,7 +113,7 @@
 void CallingConvEmitter::EmitAction(Record *Action,
                                     unsigned Indent, raw_ostream &O) {
   std::string IndentStr = std::string(Indent, ' ');
-  
+
   if (Action->isSubClassOf("CCPredicateAction")) {
     O << IndentStr << "if (";
     
@@ -121,18 +141,30 @@
       O << IndentStr << "if (!" << CC->getName()
         << "(ValNo, ValVT, LocVT, LocInfo, ArgFlags, State))\n"
         << IndentStr << "  return false;\n";
+      DelegateToMap[CurrentAction].insert(CC->getName().str());
     } else if (Action->isSubClassOf("CCAssignToReg")) {
       ListInit *RegList = Action->getValueAsListInit("RegList");
       if (RegList->size() == 1) {
-        O << IndentStr << "if (unsigned Reg = State.AllocateReg(";
-        O << getQualifiedName(RegList->getElementAsRecord(0)) << ")) {\n";
+        std::string Name = getQualifiedName(RegList->getElementAsRecord(0));
+        O << IndentStr << "if (unsigned Reg = State.AllocateReg("
+          << Name << ")) {\n";
+        if (SwiftAction)
+          AssignedSwiftRegsMap[CurrentAction].insert(Name);
+        else
+          AssignedRegsMap[CurrentAction].insert(Name);
       } else {
         O << IndentStr << "static const MCPhysReg RegList" << ++Counter
           << "[] = {\n";
         O << IndentStr << "  ";
         ListSeparator LS;
-        for (unsigned i = 0, e = RegList->size(); i != e; ++i)
-          O << LS << getQualifiedName(RegList->getElementAsRecord(i));
+        for (unsigned i = 0, e = RegList->size(); i != e; ++i) {
+          std::string Name = getQualifiedName(RegList->getElementAsRecord(i));
+          if (SwiftAction)
+            AssignedSwiftRegsMap[CurrentAction].insert(Name);
+          else
+            AssignedRegsMap[CurrentAction].insert(Name);
+          O << LS << Name;
+        }
         O << "\n" << IndentStr << "};\n";
         O << IndentStr << "if (unsigned Reg = State.AllocateReg(RegList"
           << Counter << ")) {\n";
@@ -287,6 +319,63 @@
   }
 }
 
+void CallingConvEmitter::EmitArgRegisterLists(raw_ostream &O) {
+  using EntryTy = std::pair<std::string, std::set<std::string>>;
+
+  // Transitively merge all delegated CCs into AssignedRegsMap.
+restart:
+  for (EntryTy Entry : DelegateToMap) {
+    if (!Entry.second.empty())
+      continue;
+
+    for (EntryTy Entry2 : DelegateToMap) {
+      if (Entry2.second.find(Entry.first) != Entry2.second.end()) {
+        AssignedRegsMap[Entry2.first].insert(
+            AssignedRegsMap[Entry.first].begin(),
+            AssignedRegsMap[Entry.first].end());
+        Entry2.second.erase(Entry.first);
+      }
+    }
+
+    DelegateToMap.erase(Entry.first);
+    goto restart;
+  }
+
+  if (AssignedRegsMap.empty())
+    return;
+
+  O << "\n";
+  for (EntryTy Entry : AssignedRegsMap) {
+    if (Entry.first.empty()) continue;
+
+    O << "const MCRegister " << Entry.first << "_ArgRegs[] = { ";
+
+    if (Entry.second.empty()) {
+      O << "0";
+    } else {
+      ListSeparator LS;
+      for (const std::string &Reg : Entry.second)
+        O << LS << Reg;
+    }
+
+    O << " };\n";
+  }
+
+  if (AssignedSwiftRegsMap.empty())
+    return;
+
+  O << "\n// Registers used by Swift.\n";
+  for (EntryTy Entry : AssignedSwiftRegsMap) {
+    O << "const MCRegister " << Entry.first << "_Swift_ArgRegs[] = { ";
+
+    ListSeparator LS;
+    for (const std::string &Reg : Entry.second)
+      O << LS << Reg;
+
+    O << " };\n";
+  }
+}
+
 namespace llvm {
 
 void EmitCallingConv(RecordKeeper &RK, raw_ostream &OS) {
Index: llvm/test/CodeGen/AArch64/zero-call-used-regs.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/AArch64/zero-call-used-regs.ll
@@ -0,0 +1,233 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=aarch64-unknown-unknown | FileCheck %s
+
+@result = dso_local global i32 0, align 4
+
+define dso_local i32 @skip(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 "zero-call-used-regs"="skip" {
+; CHECK-LABEL: skip:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @used_gpr_arg(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 noinline optnone "zero-call-used-regs"="used-gpr-arg" {
+; CHECK-LABEL: used_gpr_arg:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @used_gpr(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 noinline optnone "zero-call-used-regs"="used-gpr" {
+; CHECK-LABEL: used_gpr:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    mov x8, #0
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @used_arg(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 noinline optnone "zero-call-used-regs"="used-arg" {
+; CHECK-LABEL: used_arg:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @used(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 noinline optnone "zero-call-used-regs"="used" {
+; CHECK-LABEL: used:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    mov x8, #0
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @all_gpr_arg(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 "zero-call-used-regs"="all-gpr-arg" {
+; CHECK-LABEL: all_gpr_arg:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x3, #0
+; CHECK-NEXT:    mov x4, #0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    mov x5, #0
+; CHECK-NEXT:    mov x6, #0
+; CHECK-NEXT:    mov x7, #0
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @all_gpr(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 "zero-call-used-regs"="all-gpr" {
+; CHECK-LABEL: all_gpr:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x3, #0
+; CHECK-NEXT:    mov x4, #0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    mov x5, #0
+; CHECK-NEXT:    mov x6, #0
+; CHECK-NEXT:    mov x7, #0
+; CHECK-NEXT:    mov x8, #0
+; CHECK-NEXT:    mov x9, #0
+; CHECK-NEXT:    mov x10, #0
+; CHECK-NEXT:    mov x11, #0
+; CHECK-NEXT:    mov x12, #0
+; CHECK-NEXT:    mov x13, #0
+; CHECK-NEXT:    mov x14, #0
+; CHECK-NEXT:    mov x15, #0
+; CHECK-NEXT:    mov x16, #0
+; CHECK-NEXT:    mov x17, #0
+; CHECK-NEXT:    mov x18, #0
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @all_arg(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 "zero-call-used-regs"="all-arg" {
+; CHECK-LABEL: all_arg:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x3, #0
+; CHECK-NEXT:    mov x4, #0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    mov x5, #0
+; CHECK-NEXT:    mov x6, #0
+; CHECK-NEXT:    mov x7, #0
+; CHECK-NEXT:    movi q0, #0000000000000000
+; CHECK-NEXT:    movi q1, #0000000000000000
+; CHECK-NEXT:    movi q2, #0000000000000000
+; CHECK-NEXT:    movi q3, #0000000000000000
+; CHECK-NEXT:    movi q4, #0000000000000000
+; CHECK-NEXT:    movi q5, #0000000000000000
+; CHECK-NEXT:    movi q6, #0000000000000000
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+define dso_local i32 @all(i32 noundef %a, i32 noundef %b, i32 noundef %c) local_unnamed_addr #0 "zero-call-used-regs"="all" {
+; CHECK-LABEL: all:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mul w8, w1, w0
+; CHECK-NEXT:    mov x1, #0
+; CHECK-NEXT:    mov x3, #0
+; CHECK-NEXT:    mov x4, #0
+; CHECK-NEXT:    orr w0, w8, w2
+; CHECK-NEXT:    mov x2, #0
+; CHECK-NEXT:    mov x5, #0
+; CHECK-NEXT:    mov x6, #0
+; CHECK-NEXT:    mov x7, #0
+; CHECK-NEXT:    mov x8, #0
+; CHECK-NEXT:    mov x9, #0
+; CHECK-NEXT:    mov x10, #0
+; CHECK-NEXT:    mov x11, #0
+; CHECK-NEXT:    mov x12, #0
+; CHECK-NEXT:    mov x13, #0
+; CHECK-NEXT:    mov x14, #0
+; CHECK-NEXT:    mov x15, #0
+; CHECK-NEXT:    mov x16, #0
+; CHECK-NEXT:    mov x17, #0
+; CHECK-NEXT:    mov x18, #0
+; CHECK-NEXT:    movi q0, #0000000000000000
+; CHECK-NEXT:    movi q1, #0000000000000000
+; CHECK-NEXT:    movi q2, #0000000000000000
+; CHECK-NEXT:    movi q3, #0000000000000000
+; CHECK-NEXT:    movi q4, #0000000000000000
+; CHECK-NEXT:    movi q5, #0000000000000000
+; CHECK-NEXT:    movi q6, #0000000000000000
+; CHECK-NEXT:    movi q7, #0000000000000000
+; CHECK-NEXT:    movi q8, #0000000000000000
+; CHECK-NEXT:    movi q9, #0000000000000000
+; CHECK-NEXT:    movi q10, #0000000000000000
+; CHECK-NEXT:    movi q11, #0000000000000000
+; CHECK-NEXT:    movi q12, #0000000000000000
+; CHECK-NEXT:    movi q13, #0000000000000000
+; CHECK-NEXT:    movi q14, #0000000000000000
+; CHECK-NEXT:    movi q15, #0000000000000000
+; CHECK-NEXT:    movi q16, #0000000000000000
+; CHECK-NEXT:    movi q17, #0000000000000000
+; CHECK-NEXT:    movi q18, #0000000000000000
+; CHECK-NEXT:    movi q19, #0000000000000000
+; CHECK-NEXT:    movi q20, #0000000000000000
+; CHECK-NEXT:    movi q21, #0000000000000000
+; CHECK-NEXT:    movi q22, #0000000000000000
+; CHECK-NEXT:    movi q23, #0000000000000000
+; CHECK-NEXT:    movi q24, #0000000000000000
+; CHECK-NEXT:    movi q25, #0000000000000000
+; CHECK-NEXT:    movi q26, #0000000000000000
+; CHECK-NEXT:    movi q27, #0000000000000000
+; CHECK-NEXT:    movi q28, #0000000000000000
+; CHECK-NEXT:    movi q29, #0000000000000000
+; CHECK-NEXT:    movi q30, #0000000000000000
+; CHECK-NEXT:    movi q31, #0000000000000000
+; CHECK-NEXT:    ret
+
+entry:
+  %mul = mul nsw i32 %b, %a
+  %or = or i32 %mul, %c
+  ret i32 %or
+}
+
+; Don't emit zeroing registers in "main" function.
+define dso_local i32 @main() local_unnamed_addr #0 {
+; CHECK-LABEL: main:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mov w0, wzr
+; CHECK-NEXT:    ret
+
+entry:
+  ret i32 0
+}
+
+attributes #0 = { mustprogress nofree norecurse nosync nounwind readnone willreturn uwtable "frame-pointer"="non-leaf" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+neon,+v8a" }
Index: llvm/lib/Target/X86/X86RegisterInfo.cpp
===================================================================
--- llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -656,7 +656,7 @@
                    [&](MCRegister &RegA) { return IsSubReg(RegA, Reg); }))
     return true;
 
-  return false;
+  return X86GenRegisterInfo::isArgumentRegister(MF, Reg);
 }
 
 bool X86RegisterInfo::isFixedRegister(const MachineFunction &MF,
Index: llvm/lib/Target/AArch64/AArch64RegisterInfo.td
===================================================================
--- llvm/lib/Target/AArch64/AArch64RegisterInfo.td
+++ llvm/lib/Target/AArch64/AArch64RegisterInfo.td
@@ -1385,3 +1385,33 @@
     return AArch64SVCR::lookupSVCRByEncoding(MCOp.getImm()) != nullptr;
   }];
 }
+
+//===----------------------------------------------------------------------===//
+// Register categories.
+//
+
+def GeneralPurposeRegisters : RegisterCategory<[GPR64, GPR32]>;
+
+def GPR_ARG : RegisterClass<"AArch64", [i64, i32], 64,
+                            (add (sequence "X%u", 0, 7),
+                                 (sequence "W%u", 0, 7))>;
+def FPR8_ARG : RegisterClass<"AArch64", [untyped], 8, (trunc FPR8, 7)> {
+  let Size = 8;
+}
+def FPR16_ARG : RegisterClass<"AArch64", [f16, bf16], 16, (trunc FPR16, 7)> {
+  let Size = 16;
+}
+def FPR32_ARG : RegisterClass<"AArch64", [f32, i32], 32, (trunc FPR32, 7)>;
+def FPR64_ARG : RegisterClass<"AArch64",
+                              [f64, i64, v2f32, v1f64, v8i8, v4i16, v2i32,
+                               v1i64, v4f16, v4bf16], 64,
+                              (trunc FPR64, 7)>;
+def FPR128_ARG : RegisterClass<"AArch64",
+                                [v16i8, v8i16, v4i32, v2i64, v4f32, v2f64,
+                                 f128, v8f16, v8bf16], 128,
+                                (trunc FPR128, 7)>;
+def ArgumentRegisters : RegisterCategory<[GPR_ARG, FPR8_ARG, FPR16_ARG,
+                                          FPR32_ARG, FPR64_ARG, FPR128_ARG]>;
+
+def FIXED_REGS : RegisterClass<"AArch64", [i64], 64, (add FP, SP, VG, FFR)>;
+def FixedRegisters : RegisterCategory<[CCR, FIXED_REGS]>;
Index: llvm/lib/Target/AArch64/AArch64FrameLowering.h
===================================================================
--- llvm/lib/Target/AArch64/AArch64FrameLowering.h
+++ llvm/lib/Target/AArch64/AArch64FrameLowering.h
@@ -153,6 +153,10 @@
                                   MachineBasicBlock::iterator MBBI) const;
   void emitCalleeSavedSVERestores(MachineBasicBlock &MBB,
                                   MachineBasicBlock::iterator MBBI) const;
+
+  /// Emit target zero call-used regs.
+  void emitZeroCallUsedRegs(BitVector RegsToZero,
+                            MachineBasicBlock &MBB) const override;
 };
 
 } // End llvm namespace
Index: llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
===================================================================
--- llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -675,6 +675,138 @@
   emitCalleeSavedRestores(MBB, MBBI, true);
 }
 
+static MCRegister getRegisterOrZero(MCRegister Reg, bool HasSVE) {
+  switch (Reg.id()) {
+  default:
+    // The called routine is expected to preserve r19-r28
+    // r29 and r30 are used as frame pointer and link register resp.
+    return 0;
+
+    // GPRs
+#define CASE(n)                                                                \
+  case AArch64::W##n:                                                          \
+  case AArch64::X##n:                                                          \
+    return AArch64::X##n
+  CASE(0);
+  CASE(1);
+  CASE(2);
+  CASE(3);
+  CASE(4);
+  CASE(5);
+  CASE(6);
+  CASE(7);
+  CASE(8);
+  CASE(9);
+  CASE(10);
+  CASE(11);
+  CASE(12);
+  CASE(13);
+  CASE(14);
+  CASE(15);
+  CASE(16);
+  CASE(17);
+  CASE(18);
+#undef CASE
+
+    // FPRs
+#define CASE(n)                                                                \
+  case AArch64::B##n:                                                          \
+  case AArch64::H##n:                                                          \
+  case AArch64::S##n:                                                          \
+  case AArch64::D##n:                                                          \
+  case AArch64::Q##n:                                                          \
+    return HasSVE ? AArch64::Z##n : AArch64::Q##n
+  CASE(0);
+  CASE(1);
+  CASE(2);
+  CASE(3);
+  CASE(4);
+  CASE(5);
+  CASE(6);
+  CASE(7);
+  CASE(8);
+  CASE(9);
+  CASE(10);
+  CASE(11);
+  CASE(12);
+  CASE(13);
+  CASE(14);
+  CASE(15);
+  CASE(16);
+  CASE(17);
+  CASE(18);
+  CASE(19);
+  CASE(20);
+  CASE(21);
+  CASE(22);
+  CASE(23);
+  CASE(24);
+  CASE(25);
+  CASE(26);
+  CASE(27);
+  CASE(28);
+  CASE(29);
+  CASE(30);
+  CASE(31);
+#undef CASE
+  }
+}
+
+void AArch64FrameLowering::emitZeroCallUsedRegs(BitVector RegsToZero,
+                                                MachineBasicBlock &MBB) const {
+  // Insertion point.
+  MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator();
+
+  // Fake a debug loc.
+  DebugLoc DL;
+  if (MBBI != MBB.end())
+    DL = MBBI->getDebugLoc();
+
+  const MachineFunction &MF = *MBB.getParent();
+  const AArch64Subtarget &STI = MF.getSubtarget<AArch64Subtarget>();
+  const AArch64RegisterInfo &TRI = *STI.getRegisterInfo();
+
+  for (MCRegister Reg : RegsToZero.set_bits()) {
+    llvm::errs() << TRI.getRegAsmName(Reg) << "\n";
+  }
+
+  BitVector GPRsToZero(TRI.getNumRegs());
+  BitVector FPRsToZero(TRI.getNumRegs());
+  for (MCRegister Reg : RegsToZero.set_bits()) {
+    if (TRI.isGeneralPurposeRegister(MF, Reg)) {
+      // For GPRs, we only care to clear out the 64-bit register.
+      if (MCRegister XReg = getRegisterOrZero(Reg, STI.hasSVE()))
+        GPRsToZero.set(XReg);
+    } else if (AArch64::FPR128RegClass.contains(Reg)) {
+      // For FPRs,
+      if (MCRegister XReg = getRegisterOrZero(Reg, STI.hasSVE()))
+        FPRsToZero.set(XReg);
+    }
+  }
+
+  const AArch64InstrInfo &TII = *STI.getInstrInfo();
+
+  // Zero out GPRs.
+  for (MCRegister Reg : GPRsToZero.set_bits())
+    BuildMI(MBB, MBBI, DL, TII.get(AArch64::MOVi64imm), Reg).addImm(0);
+
+  // Zero out FP/vector registers.
+  for (MCRegister Reg : FPRsToZero.set_bits())
+    BuildMI(MBB, MBBI, DL, TII.get(AArch64::MOVID), Reg).addImm(0);
+
+  if (STI.hasSVE()) {
+    for (MCRegister PReg : {
+          AArch64::P0, AArch64::P1, AArch64::P2, AArch64::P3, AArch64::P4,
+          AArch64::P5, AArch64::P6, AArch64::P7, AArch64::P8, AArch64::P9,
+          AArch64::P10, AArch64::P11, AArch64::P12, AArch64::P13, AArch64::P14,
+          AArch64::P15
+    }) {
+      if (RegsToZero[PReg])
+        BuildMI(MBB, MBBI, DL, TII.get(AArch64::PFALSE), PReg);
+    }
+  }
+}
+
 // Find a scratch register that we can use at the start of the prologue to
 // re-align the stack pointer.  We avoid using callee-save registers since they
 // may appear to be free when this is called from canUseAsPrologue (during
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -5987,7 +5987,7 @@
     // FIXME: There's no reason for this to be restricted to X86. The backend
     // code needs to be changed to include the appropriate function calls
     // automatically.
-    if (!Triple.isX86())
+    if (!Triple.isX86() && !Triple.isAArch64())
       D.Diag(diag::err_drv_unsupported_opt_for_target)
           << A->getAsString(Args) << TripleStr;
   }
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -2977,7 +2977,7 @@
 
 def fzero_call_used_regs_EQ
     : Joined<["-"], "fzero-call-used-regs=">, Group<f_Group>, Flags<[CC1Option]>,
-      HelpText<"Clear call-used registers upon function return.">,
+      HelpText<"Clear call-used registers upon function return (AArch64/x86 only)">,
       Values<"skip,used-gpr-arg,used-gpr,used-arg,used,all-gpr-arg,all-gpr,all-arg,all">,
       NormalizedValues<["Skip", "UsedGPRArg", "UsedGPR", "UsedArg", "Used",
                         "AllGPRArg", "AllGPR", "AllArg", "All"]>,
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