[X86] add dwarf information for loop stack probe

[erikdesjardins]

Summary

This patch is based on https://reviews.llvm.org/D99585.

While inside the stack probing loop, temporarily change the CFA
to be based on r11/eax, which are already used to hold the loop bound.
The stack pointer cannot be used for CFI here as it changes during the loop,
so it does not have a constant offset to the CFA.

Co-authored-by: YangKeao <[e-mail]>

[erikdesjardins]

improve description

[pengfei]

llvm/lib/Target/X86/X86FrameLowering.cpp

698–699

alignDown(Offset, StackProbeSize)

[erikdesjardins]

use alignDown

[pengfei]

LGTM, but I'm not expert on dwarf directives. I'd like others to sign off.

[nagisa]

LGTM after the code change is applied.

llvm/lib/Target/X86/X86FrameLowering.cpp

715–720

llvm/test/CodeGen/X86/stack-clash-large.ll

19–20

In theory this could also be .cfi_def_cfa %rsp, 71888 but seems like it may be non-trivial to make it happen.

[erikdesjardins]

add test demonstrating adjust

llvm/lib/Target/X86/X86FrameLowering.cpp

715–720

It's necessary to use adjust instead of def in case there are any CFA offset changes earlier in the prologue, i.e. due to push. Added a test demonstrating this.

It would surely be possible to pass down the current CFA offset through TargetFrameLowering::inlineStackProbe, allowing us to use def here, but I think it's likely nontrivial for the same reason your other comment is nontrivial.

llvm/test/CodeGen/X86/stack-clash-large.ll

19–20

Yep, I had the same thought and came to the same conclusion.

[erikdesjardins]

Please commit this on my behalf: Erik Desjardins <[e-mail]>

llvm/lib/Target/X86/X86FrameLowering.cpp

 }
 
 void X86FrameLowering::emitStackProbeInlineGenericLoop(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator MBBI, const DebugLoc &DL, uint64_t Offset,
     uint64_t AlignOffset) const {
   assert(Offset && "null offset");
 
+  const bool NeedsDwarfCFI = needsDwarfCFI(MF);
+  const bool HasFP = hasFP(MF);
   const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
   const X86TargetLowering &TLI = *STI.getTargetLowering();
   const unsigned MovMIOpc = Is64Bit ? X86::MOV64mi32 : X86::MOV32mi;
   const uint64_t StackProbeSize = TLI.getStackProbeSize(MF);
 
   if (AlignOffset) {
     if (AlignOffset < StackProbeSize) {
       // Perform a first smaller allocation followed by a probe.
void X86FrameLowering::emitStackProbeInlineGenericLoop(
 
   MachineFunction::iterator MBBIter = ++MBB.getIterator();
   MF.insert(MBBIter, testMBB);
   MF.insert(MBBIter, tailMBB);
 
   Register FinalStackProbed = Uses64BitFramePtr ? X86::R11
                               : Is64Bit         ? X86::R11D
                                                 : X86::EAX;
+
   BuildMI(MBB, MBBI, DL, TII.get(TargetOpcode::COPY), FinalStackProbed)
       .addReg(StackPtr)
       .setMIFlag(MachineInstr::FrameSetup);
 
   // save loop bound
   {
-    const unsigned SUBOpc = getSUBriOpcode(Uses64BitFramePtr, Offset);
+    const unsigned BoundOffset = alignDown(Offset, StackProbeSize);
+    const unsigned SUBOpc = getSUBriOpcode(Uses64BitFramePtr, BoundOffset);
     BuildMI(MBB, MBBI, DL, TII.get(SUBOpc), FinalStackProbed)
         .addReg(FinalStackProbed)
-        .addImm(Offset / StackProbeSize * StackProbeSize)
+        .addImm(BoundOffset)
         .setMIFlag(MachineInstr::FrameSetup);
+
+    // while in the loop, use loop-invariant reg for CFI,
+    // instead of the stack pointer, which changes during the loop
+    if (!HasFP && NeedsDwarfCFI) {
+      // x32 uses the same DWARF register numbers as x86-64,
+      // so there isn't a register number for r11d, we must use r11 instead
+      const Register DwarfFinalStackProbed =
+          STI.isTarget64BitILP32()
+              ? Register(getX86SubSuperRegister(FinalStackProbed, 64))
+              : FinalStackProbed;
+
+      BuildCFI(MBB, MBBI, DL,
+               MCCFIInstruction::createDefCfaRegister(
+                   nullptr, TRI->getDwarfRegNum(DwarfFinalStackProbed, true)));
+      BuildCFI(MBB, MBBI, DL,
+               MCCFIInstruction::createAdjustCfaOffset(nullptr, BoundOffset));
+    }
   }
 
   // allocate a page
   {
     const unsigned SUBOpc = getSUBriOpcode(Uses64BitFramePtr, StackProbeSize);
     BuildMI(testMBB, DL, TII.get(SUBOpc), StackPtr)
         .addReg(StackPtr)
         .addImm(StackProbeSize)
void X86FrameLowering::emitStackProbeInlineGenericLoop(
   testMBB->addSuccessor(tailMBB);
 
   // BB management
   tailMBB->splice(tailMBB->end(), &MBB, MBBI, MBB.end());
   tailMBB->transferSuccessorsAndUpdatePHIs(&MBB);
   MBB.addSuccessor(testMBB);
 
   // handle tail
-  unsigned TailOffset = Offset % StackProbeSize;
+  const unsigned TailOffset = Offset % StackProbeSize;
+  MachineBasicBlock::iterator TailMBBIter = tailMBB->begin();
   if (TailOffset) {
     const unsigned Opc = getSUBriOpcode(Uses64BitFramePtr, TailOffset);
-    BuildMI(*tailMBB, tailMBB->begin(), DL, TII.get(Opc), StackPtr)
+    BuildMI(*tailMBB, TailMBBIter, DL, TII.get(Opc), StackPtr)
         .addReg(StackPtr)
         .addImm(TailOffset)
         .setMIFlag(MachineInstr::FrameSetup);
   }
 
+  // after the loop, switch back to stack pointer for CFI
+  if (!HasFP && NeedsDwarfCFI) {
+    // x32 uses the same DWARF register numbers as x86-64,
+    // so there isn't a register number for esp, we must use rsp instead
+    const Register DwarfStackPtr =
+        STI.isTarget64BitILP32()
+            ? Register(getX86SubSuperRegister(StackPtr, 64))
+            : Register(StackPtr);
+
+    BuildCFI(*tailMBB, TailMBBIter, DL,
+             MCCFIInstruction::createDefCfaRegister(
+                 nullptr, TRI->getDwarfRegNum(DwarfStackPtr, true)));
+  }
+
   // Update Live In information
   recomputeLiveIns(*testMBB);
   recomputeLiveIns(*tailMBB);
 }
 
 void X86FrameLowering::emitStackProbeInlineWindowsCoreCLR64(
     MachineFunction &MF, MachineBasicBlock &MBB,
     MachineBasicBlock::iterator MBBI, const DebugLoc &DL, bool InProlog) const {

llvm/test/CodeGen/X86/stack-clash-large.ll

 ; RUN: llc -mtriple=x86_64-linux-android < %s | FileCheck -check-prefix=CHECK-X64 %s
 ; RUN: llc -mtriple=i686-linux-android < %s | FileCheck -check-prefix=CHECK-X86 %s
 ; RUN: llc -mtriple=x86_64-linux-gnux32 < %s | FileCheck -check-prefix=CHECK-X32 %s
 
 define i32 @foo() local_unnamed_addr #0 {
 ; CHECK-X64-LABEL: foo:
 ; CHECK-X64:       # %bb.0:
 ; CHECK-X64-NEXT:    movq %rsp, %r11
 ; CHECK-X64-NEXT:    subq $69632, %r11 # imm = 0x11000
+; CHECK-X64-NEXT:    .cfi_def_cfa_register %r11
+; CHECK-X64-NEXT:    .cfi_adjust_cfa_offset 69632
 ; CHECK-X64-NEXT:  .LBB0_1: # =>This Inner Loop Header: Depth=1
 ; CHECK-X64-NEXT:    subq $4096, %rsp # imm = 0x1000
 ; CHECK-X64-NEXT:    movq $0, (%rsp)
 ; CHECK-X64-NEXT:    cmpq %r11, %rsp
 ; CHECK-X64-NEXT:    jne .LBB0_1
 ; CHECK-X64-NEXT:  # %bb.2:
 ; CHECK-X64-NEXT:    subq $2248, %rsp # imm = 0x8C8
+; CHECK-X64-NEXT:    .cfi_def_cfa_register %rsp
 ; CHECK-X64-NEXT:    .cfi_def_cfa_offset 71888
 ; CHECK-X64-NEXT:    movl $1, 264(%rsp)
 ; CHECK-X64-NEXT:    movl $1, 28664(%rsp)
 ; CHECK-X64-NEXT:    movl -128(%rsp), %eax
 ; CHECK-X64-NEXT:    addq $71880, %rsp # imm = 0x118C8
 ; CHECK-X64-NEXT:    .cfi_def_cfa_offset 8
 ; CHECK-X64-NEXT:    retq
 ;
 ; CHECK-X86-LABEL: foo:
 ; CHECK-X86:       # %bb.0:
 ; CHECK-X86-NEXT:    movl %esp, %eax
 ; CHECK-X86-NEXT:    subl $69632, %eax # imm = 0x11000
+; CHECK-X86-NEXT:    .cfi_def_cfa_register %eax
+; CHECK-X86-NEXT:    .cfi_adjust_cfa_offset 69632
 ; CHECK-X86-NEXT:  .LBB0_1: # =>This Inner Loop Header: Depth=1
 ; CHECK-X86-NEXT:    subl $4096, %esp # imm = 0x1000
 ; CHECK-X86-NEXT:    movl $0, (%esp)
 ; CHECK-X86-NEXT:    cmpl %eax, %esp
 ; CHECK-X86-NEXT:    jne .LBB0_1
 ; CHECK-X86-NEXT:  # %bb.2:
 ; CHECK-X86-NEXT:    subl $2380, %esp # imm = 0x94C
+; CHECK-X86-NEXT:    .cfi_def_cfa_register %esp
 ; CHECK-X86-NEXT:    .cfi_def_cfa_offset 72016
 ; CHECK-X86-NEXT:    movl $1, 392(%esp)
 ; CHECK-X86-NEXT:    movl $1, 28792(%esp)
 ; CHECK-X86-NEXT:    movl (%esp), %eax
 ; CHECK-X86-NEXT:    addl $72012, %esp # imm = 0x1194C
 ; CHECK-X86-NEXT:    .cfi_def_cfa_offset 4
 ; CHECK-X86-NEXT:    retl
 ;
 ; CHECK-X32-LABEL: foo:
 ; CHECK-X32:       # %bb.0:
 ; CHECK-X32-NEXT:    movl %esp, %r11d
 ; CHECK-X32-NEXT:    subl $69632, %r11d # imm = 0x11000
+; CHECK-X32-NEXT:    .cfi_def_cfa_register %r11
+; CHECK-X32-NEXT:    .cfi_adjust_cfa_offset 69632
 ; CHECK-X32-NEXT:  .LBB0_1: # =>This Inner Loop Header: Depth=1
 ; CHECK-X32-NEXT:    subl $4096, %esp # imm = 0x1000
 ; CHECK-X32-NEXT:    movq $0, (%esp)
 ; CHECK-X32-NEXT:    cmpl %r11d, %esp
 ; CHECK-X32-NEXT:    jne .LBB0_1
 ; CHECK-X32-NEXT:  # %bb.2:
 ; CHECK-X32-NEXT:    subl $2248, %esp # imm = 0x8C8
+; CHECK-X32-NEXT:    .cfi_def_cfa_register %rsp
 ; CHECK-X32-NEXT:    .cfi_def_cfa_offset 71888
 ; CHECK-X32-NEXT:    movl $1, 264(%esp)
 ; CHECK-X32-NEXT:    movl $1, 28664(%esp)
 ; CHECK-X32-NEXT:    movl -128(%esp), %eax
 ; CHECK-X32-NEXT:    addl $71880, %esp # imm = 0x118C8
 ; CHECK-X32-NEXT:    .cfi_def_cfa_offset 8
 ; CHECK-X32-NEXT:    retq
   %a = alloca i32, i64 18000, align 16