[AArch64] "Support" debug info for SVE types on Windows. (#147865)

There isn't any way to encode a variable in an SVE register, and there
isn't any way to encode a scalable offset, and as far as I know that's
unlikely to change in the near future. So suppress any debug info which
would require those encodings.

This isn't ideal, but we need to ship something which doesn't crash.

Alternatively, for Z registers, we could emit debug info assuming the
vector length is 128 bits, but that seems like it would lead to
unintuitive results.

The change to AArch64FrameLowering is needed to avoid a crash. But we
can't actually test that the returned offset is correct: LiveDebugValues
performs the query, then discards the result.

Author: efriedma-quic

llvm/include/llvm/CodeGen/TargetRegisterInfo.h

@@ -1243,6 +1243,10 @@ class LLVM_ABI TargetRegisterInfo : public MCRegisterInfo {
   getVRegFlagsOfReg(Register Reg, const MachineFunction &MF) const {
     return {};
   }
+
+  // Whether this register should be ignored when generating CodeView debug
+  // info, because it's a known there is no mapping available.
+  virtual bool isIgnoredCVReg(MCRegister LLVMReg) const { return false; }
 };
 
 //===----------------------------------------------------------------------===//

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -1318,8 +1318,10 @@ void CodeViewDebug::collectVariableInfoFromMFTable(
         TFI->getFrameIndexReference(*Asm->MF, VI.getStackSlot(), FrameReg);
     uint16_t CVReg = TRI->getCodeViewRegNum(FrameReg);
 
-    assert(!FrameOffset.getScalable() &&
-           "Frame offsets with a scalable component are not supported");
+    if (FrameOffset.getScalable()) {
+      // No encoding currently exists for scalable offsets; bail out.
+      continue;
+    }
 
     // Calculate the label ranges.
     LocalVarDef DefRange =
@@ -1410,6 +1412,11 @@ void CodeViewDebug::calculateRanges(
       if (Location->FragmentInfo->OffsetInBits % 8)
         continue;
 
+    if (TRI->isIgnoredCVReg(Location->Register)) {
+      // No encoding currently exists for this register; bail out.
+      continue;
+    }
+
     LocalVarDef DR;
     DR.CVRegister = TRI->getCodeViewRegNum(Location->Register);
     DR.InMemory = !Location->LoadChain.empty();

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -3043,9 +3043,11 @@ StackOffset AArch64FrameLowering::resolveFrameOffsetReference(
         StackOffset::get(MFI.getStackSize() - AFI->getCalleeSavedStackSize(),
                          ObjectOffset);
     if (FPAfterSVECalleeSaves) {
-      assert(-ObjectOffset > (int64_t)AFI->getSVECalleeSavedStackSize() &&
-             "Math isn't correct for CSRs with FPAfterSVECalleeSaves");
       FPOffset += StackOffset::getScalable(AFI->getSVECalleeSavedStackSize());
+      if (-ObjectOffset <= (int64_t)AFI->getSVECalleeSavedStackSize()) {
+        FPOffset += StackOffset::getFixed(AFI->getCalleeSavedStackSize());
+        SPOffset += StackOffset::getFixed(AFI->getCalleeSavedStackSize());
+      }
     }
     // Always use the FP for SVE spills if available and beneficial.
     if (hasFP(MF) && (SPOffset.getFixed() ||

llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp

@@ -1370,3 +1370,8 @@ bool AArch64RegisterInfo::shouldAnalyzePhysregInMachineLoopInfo(
     MCRegister R) const {
   return R == AArch64::VG;
 }
+
+bool AArch64RegisterInfo::isIgnoredCVReg(MCRegister LLVMReg) const {
+  return (LLVMReg >= AArch64::Z0 && LLVMReg <= AArch64::Z31) ||
+         (LLVMReg >= AArch64::P0 && LLVMReg <= AArch64::P15);
+}

llvm/lib/Target/AArch64/AArch64RegisterInfo.h

@@ -154,6 +154,8 @@ class AArch64RegisterInfo final : public AArch64GenRegisterInfo {
                         SmallVectorImpl<uint64_t> &Ops) const override;
 
   bool shouldAnalyzePhysregInMachineLoopInfo(MCRegister R) const override;
+
+  virtual bool isIgnoredCVReg(MCRegister LLVMReg) const override;
 };
 
 } // end namespace llvm

llvm/test/DebugInfo/COFF/AArch64/codeview-sve.ll

@@ -0,0 +1,161 @@
+; RUN: llc < %s -filetype=obj | llvm-readobj --codeview - | FileCheck %s
+
+; The point of this is mostly just to avoid crashing... there isn't any way
+; to encode most of the information we want to encode.  But we try to do what
+; we can.
+;
+; Generated from:
+;
+; #include <arm_sve.h>
+; void g();
+; svint32_t f(svint32_t aaa, svint32_t bbb, svint32_t *ccc) {
+;   asm("":::"z0", "z1", "z2", "z3", "z4", "z5", "z6", "z7", "z8", "z9",
+;            "z10", "z11", "z12", "z13", "z14", "z15", "z16", "z17", "z18",
+;            "z19", "z20", "z21", "z22", "z23", "z24", "z25", "z26", "z27",
+;            "z28", "z29", "z30", "z31");
+;  return aaa**ccc+bbb;
+;}
+
+; Emit the SVE type.  We represent this as an array with unknown bound.
+
+; CHECK:      Array (0x1000) {
+; CHECK-NEXT:     TypeLeafKind: LF_ARRAY (0x1503)
+; CHECK-NEXT:     ElementType: int (0x74)
+; CHECK-NEXT:     IndexType: unsigned __int64 (0x23)
+; CHECK-NEXT:     SizeOf: 0
+; CHECK-NEXT:     Name:
+; CHECK-NEXT:   }
+
+; Emit frame information.  This is missing the size of the SVE
+; variables, but we can't really do anything about that.
+
+; CHECK:         FrameProcSym {
+; CHECK-NEXT:      Kind: S_FRAMEPROC (0x1012)
+; CHECK-NEXT:      TotalFrameBytes: 0x10
+; CHECK-NEXT:      PaddingFrameBytes: 0x0
+; CHECK-NEXT:      OffsetToPadding: 0x0
+; CHECK-NEXT:      BytesOfCalleeSavedRegisters: 0x0
+; CHECK-NEXT:      OffsetOfExceptionHandler: 0x0
+; CHECK-NEXT:      SectionIdOfExceptionHandler: 0x0
+; CHECK-NEXT:      Flags [ (0x116008)
+; CHECK-NEXT:        HasInlineAssembly (0x8)
+; CHECK-NEXT:        OptimizedForSpeed (0x100000)
+; CHECK-NEXT:        SafeBuffers (0x2000)
+; CHECK-NEXT:      ]
+; CHECK-NEXT:      LocalFramePtrReg: ARM64_NOREG (0x0)
+; CHECK-NEXT:      ParamFramePtrReg: ARM64_NOREG (0x0)
+; CHECK-NEXT:    }
+
+; Emit the symbols for the local variables.
+;
+; ccc is a normal pointer.
+;
+; We can't represent bbb anywhere in its range; there's no way to name Z
+; registers, and no way to express its location on the stack relative
+; to the stack pointer when it's spilled.
+;
+; In the middle of the range, aaa happens to have a scalable offset of zero,
+; so we can represent it while it's on the stack.
+
+; CHECK-NEXT:    LocalSym {
+; CHECK-NEXT:      Kind: S_LOCAL (0x113E)
+; CHECK-NEXT:      Type: 0x1000
+; CHECK-NEXT:      Flags [ (0x1)
+; CHECK-NEXT:        IsParameter (0x1)
+; CHECK-NEXT:      ]
+; CHECK-NEXT:      VarName: aaa
+; CHECK-NEXT:    }
+; CHECK-NEXT:    DefRangeRegisterRelSym {
+; CHECK-NEXT:      Kind: S_DEFRANGE_REGISTER_REL (0x1145)
+; CHECK-NEXT:      BaseRegister: ARM64_SP (0x51)
+; CHECK-NEXT:      HasSpilledUDTMember: No
+; CHECK-NEXT:      OffsetInParent: 0
+; CHECK-NEXT:      BasePointerOffset: 0
+; CHECK-NEXT:      LocalVariableAddrRange {
+; CHECK-NEXT:        OffsetStart: .text+0x58
+; CHECK-NEXT:        ISectStart: 0x0
+; CHECK-NEXT:        Range: 0xC
+; CHECK-NEXT:      }
+; CHECK-NEXT:    }
+; CHECK-NEXT:    LocalSym {
+; CHECK-NEXT:      Kind: S_LOCAL (0x113E)
+; CHECK-NEXT:      Type: 0x1000
+; CHECK-NEXT:      Flags [ (0x101)
+; CHECK-NEXT:        IsOptimizedOut (0x100)
+; CHECK-NEXT:        IsParameter (0x1)
+; CHECK-NEXT:      ]
+; CHECK-NEXT:      VarName: bbb
+; CHECK-NEXT:    }
+; CHECK-NEXT:    LocalSym {
+; CHECK-NEXT:      Kind: S_LOCAL (0x113E)
+; CHECK-NEXT:      Type: * (0x1001)
+; CHECK-NEXT:      Flags [ (0x1)
+; CHECK-NEXT:        IsParameter (0x1)
+; CHECK-NEXT:      ]
+; CHECK-NEXT:      VarName: ccc
+; CHECK-NEXT:    }
+; CHECK-NEXT:    DefRangeRegisterSym {
+; CHECK-NEXT:      Kind: S_DEFRANGE_REGISTER (0x1141)
+; CHECK-NEXT:      Register: ARM64_X0 (0x32)
+; CHECK-NEXT:      MayHaveNoName: 0
+; CHECK-NEXT:      LocalVariableAddrRange {
+; CHECK-NEXT:        OffsetStart: .text+0x0
+; CHECK-NEXT:        ISectStart: 0x0
+; CHECK-NEXT:        Range: 0xBC
+; CHECK-NEXT:      }
+; CHECK-NEXT:    }
+; CHECK-NEXT:    ProcEnd {
+; CHECK-NEXT:      Kind: S_PROC_ID_END (0x114F)
+; CHECK-NEXT:    }
+
+target triple = "aarch64-unknown-windows-msvc19.33.0"
+
+; Function Attrs: mustprogress nounwind uwtable vscale_range(1,16)
+define dso_local <vscale x 4 x i32> @"?f@@YAU__SVInt32_t@__clang@@U12@0PEAU12@@Z"(<vscale x 4 x i32> %aaa, <vscale x 4 x i32> %bbb, ptr noundef readonly captures(none) %ccc) local_unnamed_addr #0 !dbg !10 {
+entry:
+    #dbg_value(ptr %ccc, !23, !DIExpression(), !26)
+    #dbg_value(<vscale x 4 x i32> %bbb, !24, !DIExpression(), !26)
+    #dbg_value(<vscale x 4 x i32> %aaa, !25, !DIExpression(), !26)
+  tail call void asm sideeffect "", "~{z0},~{z1},~{z2},~{z3},~{z4},~{z5},~{z6},~{z7},~{z8},~{z9},~{z10},~{z11},~{z12},~{z13},~{z14},~{z15},~{z16},~{z17},~{z18},~{z19},~{z20},~{z21},~{z22},~{z23},~{z24},~{z25},~{z26},~{z27},~{z28},~{z29},~{z30},~{z31}"() #1, !dbg !27, !srcloc !28
+  %0 = load <vscale x 4 x i32>, ptr %ccc, align 16, !dbg !27
+  %mul = mul <vscale x 4 x i32> %0, %aaa, !dbg !27
+  %add = add <vscale x 4 x i32> %mul, %bbb, !dbg !27
+  ret <vscale x 4 x i32> %add, !dbg !27
+}
+
+attributes #0 = { mustprogress nounwind uwtable vscale_range(1,16) "frame-pointer"="non-leaf" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+fp-armv8,+fullfp16,+neon,+sve,+v8a,-fmv" }
+attributes #1 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 21.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "-", directory: "", checksumkind: CSK_MD5, checksum: "e54fc2ba768e4a43f64b8a9d03a374d6")
+!2 = !{i32 2, !"CodeView", i32 1}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 2}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"uwtable", i32 2}
+!7 = !{i32 7, !"frame-pointer", i32 1}
+!8 = !{i32 7, !"debug-info-assignment-tracking", i1 true}
+!9 = !{!"clang version 21.0.0git"}
+!10 = distinct !DISubprogram(name: "f", linkageName: "?f@@YAU__SVInt32_t@__clang@@U12@0PEAU12@@Z", scope: !11, file: !11, line: 2, type: !12, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !22)
+!11 = !DIFile(filename: "<stdin>", directory: "", checksumkind: CSK_MD5, checksum: "e54fc2ba768e4a43f64b8a9d03a374d6")
+!12 = !DISubroutineType(types: !13)
+!13 = !{!14, !14, !14, !21}
+!14 = !DIDerivedType(tag: DW_TAG_typedef, name: "svint32_t", file: !15, line: 30, baseType: !16)
+!15 = !DIFile(filename: "arm_sve.h", directory: "", checksumkind: CSK_MD5, checksum: "34027e9d24f4b03c6e5370869d5cc907")
+!16 = !DIDerivedType(tag: DW_TAG_typedef, name: "__SVInt32_t", file: !1, baseType: !17)
+!17 = !DICompositeType(tag: DW_TAG_array_type, baseType: !18, flags: DIFlagVector, elements: !19)
+!18 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!19 = !{!20}
+!20 = !DISubrange(lowerBound: 0, upperBound: !DIExpression(DW_OP_constu, 2, DW_OP_bregx, 46, 0, DW_OP_mul, DW_OP_constu, 1, DW_OP_minus))
+!21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64)
+!22 = !{!23, !24, !25}
+!23 = !DILocalVariable(name: "ccc", arg: 3, scope: !10, file: !11, line: 2, type: !21)
+!24 = !DILocalVariable(name: "bbb", arg: 2, scope: !10, file: !11, line: 2, type: !14)
+!25 = !DILocalVariable(name: "aaa", arg: 1, scope: !10, file: !11, line: 2, type: !14)
+!26 = !DILocation(line: 0, scope: !10)
+!27 = !DILocation(line: 2, scope: !10)
+!28 = !{i64 98}