Spill/restore FP/BP around instructions in which they are clobbered (#…

…81048)

This patch fixes #17204.

If a base pointer is used in a function, and it is clobbered by an
instruction (typically an inline asm), current register allocator can't
handle this situation, so BP becomes garbage after those instructions.
It can also occur to FP in theory.

We can spill and reload FP/BP registers around those instructions. But
normal spill/reload instructions also use FP/BP, so we can't spill them
into normal spill slots, instead we spill them into the top of stack by
using SP register.

llvm/include/llvm/CodeGen/TargetFrameLowering.h

@@ -475,6 +475,10 @@ class TargetFrameLowering {
   /// debug info.
   virtual DwarfFrameBase getDwarfFrameBase(const MachineFunction &MF) const;
 
+  /// If frame pointer or base pointer is clobbered by an instruction, we should
+  /// spill/restore it around that instruction.
+  virtual void spillFPBP(MachineFunction &MF) const {}
+
   /// This method is called at the end of prolog/epilog code insertion, so
   /// targets can emit remarks based on the final frame layout.
   virtual void emitRemarks(const MachineFunction &MF,

llvm/lib/CodeGen/CFIInstrInserter.cpp

@@ -25,6 +25,7 @@
 #include "llvm/CodeGen/TargetInstrInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDwarf.h"
 using namespace llvm;
 
@@ -184,6 +185,10 @@ void CFIInstrInserter::calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo) {
   unsigned NumRegs = TRI.getNumSupportedRegs(*MF);
   BitVector CSRSaved(NumRegs), CSRRestored(NumRegs);
 
+#ifndef NDEBUG
+  int RememberState = 0;
+#endif
+
   // Determine cfa offset and register set by the block.
   for (MachineInstr &MI : *MBBInfo.MBB) {
     if (MI.isCFIInstruction()) {
@@ -228,17 +233,25 @@ void CFIInstrInserter::calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo) {
       case MCCFIInstruction::OpRememberState:
         // TODO: Add support for handling cfi_remember_state.
 #ifndef NDEBUG
-        report_fatal_error(
-            "Support for cfi_remember_state not implemented! Value of CFA "
-            "may be incorrect!\n");
+        // Currently we need cfi_remember_state and cfi_restore_state to be in
+        // the same BB, so it will not impact outgoing CFA.
+        ++RememberState;
+        if (RememberState != 1)
+          MF->getContext().reportError(
+              SMLoc(),
+              "Support for cfi_remember_state not implemented! Value of CFA "
+              "may be incorrect!\n");
 #endif
         break;
       case MCCFIInstruction::OpRestoreState:
         // TODO: Add support for handling cfi_restore_state.
 #ifndef NDEBUG
-        report_fatal_error(
-            "Support for cfi_restore_state not implemented! Value of CFA may "
-            "be incorrect!\n");
+        --RememberState;
+        if (RememberState != 0)
+          MF->getContext().reportError(
+              SMLoc(),
+              "Support for cfi_restore_state not implemented! Value of CFA may "
+              "be incorrect!\n");
 #endif
         break;
       // Other CFI directives do not affect CFA value.
@@ -264,6 +277,14 @@ void CFIInstrInserter::calculateOutgoingCFAInfo(MBBCFAInfo &MBBInfo) {
     }
   }
 
+#ifndef NDEBUG
+  if (RememberState != 0)
+    MF->getContext().reportError(
+        SMLoc(),
+        "Support for cfi_remember_state not implemented! Value of CFA may be "
+        "incorrect!\n");
+#endif
+
   MBBInfo.Processed = true;
 
   // Update outgoing CFA info.

llvm/lib/CodeGen/PrologEpilogInserter.cpp

@@ -228,6 +228,11 @@ bool PEI::runOnMachineFunction(MachineFunction &MF) {
   FrameIndexVirtualScavenging = TRI->requiresFrameIndexScavenging(MF);
   ORE = &getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE();
 
+  // Spill frame pointer and/or base pointer registers if they are clobbered.
+  // It is placed before call frame instruction elimination so it will not mess
+  // with stack arguments.
+  TFI->spillFPBP(MF);
+
   // Calculate the MaxCallFrameSize value for the function's frame
   // information. Also eliminates call frame pseudo instructions.
   calculateCallFrameInfo(MF);