rust-lang · nikic · Jul 9, 2025 · Jul 7, 2025
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -428,19 +428,38 @@ AArch64FrameLowering::getStackIDForScalableVectors() const {
 static unsigned getFixedObjectSize(const MachineFunction &MF,
                                    const AArch64FunctionInfo *AFI, bool IsWin64,
                                    bool IsFunclet) {
+  assert(AFI->getTailCallReservedStack() % 16 == 0 &&
+         "Tail call reserved stack must be aligned to 16 bytes");
   if (!IsWin64 || IsFunclet) {
     return AFI->getTailCallReservedStack();
   } else {
     if (AFI->getTailCallReservedStack() != 0 &&
         !MF.getFunction().getAttributes().hasAttrSomewhere(
             Attribute::SwiftAsync))
       report_fatal_error("cannot generate ABI-changing tail call for Win64");
+    unsigned FixedObjectSize = AFI->getTailCallReservedStack();
+
     // Var args are stored here in the primary function.
-    const unsigned VarArgsArea = AFI->getVarArgsGPRSize();
-    // To support EH funclets we allocate an UnwindHelp object
-    const unsigned UnwindHelpObject = (MF.hasEHFunclets() ? 8 : 0);
-    return AFI->getTailCallReservedStack() +
-           alignTo(VarArgsArea + UnwindHelpObject, 16);
+    FixedObjectSize += AFI->getVarArgsGPRSize();
+
+    if (MF.hasEHFunclets()) {
+      // Catch objects are stored here in the primary function.
+      const MachineFrameInfo &MFI = MF.getFrameInfo();
+      const WinEHFuncInfo &EHInfo = *MF.getWinEHFuncInfo();
+      for (const WinEHTryBlockMapEntry &TBME : EHInfo.TryBlockMap) {
+        for (const WinEHHandlerType &H : TBME.HandlerArray) {
+          int FrameIndex = H.CatchObj.FrameIndex;
+          if (FrameIndex != INT_MAX) {
+            FixedObjectSize = alignTo(FixedObjectSize,
+                                      MFI.getObjectAlign(FrameIndex).value()) +
+                              MFI.getObjectSize(FrameIndex);
+          }
+        }
+      }
+      // To support EH funclets we allocate an UnwindHelp object
+      FixedObjectSize += 8;
+    }
+    return alignTo(FixedObjectSize, 16);
   }
 }
 
@@ -4494,30 +4513,47 @@ void AArch64FrameLowering::processFunctionBeforeFrameFinalized(
   // anything.
   if (!MF.hasEHFunclets())
     return;
-  const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
-  WinEHFuncInfo &EHInfo = *MF.getWinEHFuncInfo();
 
-  MachineBasicBlock &MBB = MF.front();
-  auto MBBI = MBB.begin();
-  while (MBBI != MBB.end() && MBBI->getFlag(MachineInstr::FrameSetup))
-    ++MBBI;
+  // Win64 C++ EH needs to allocate space for the catch objects in the fixed
+  // object area right next to the UnwindHelp object.
+  WinEHFuncInfo &EHInfo = *MF.getWinEHFuncInfo();
+  int64_t CurrentOffset =
+      AFI->getVarArgsGPRSize() + AFI->getTailCallReservedStack();
+  for (WinEHTryBlockMapEntry &TBME : EHInfo.TryBlockMap) {
+    for (WinEHHandlerType &H : TBME.HandlerArray) {
+      int FrameIndex = H.CatchObj.FrameIndex;
+      if (FrameIndex != INT_MAX) {
+        CurrentOffset =
+            alignTo(CurrentOffset, MFI.getObjectAlign(FrameIndex).value());
+        CurrentOffset += MFI.getObjectSize(FrameIndex);
+        MFI.setObjectOffset(FrameIndex, -CurrentOffset);
+      }
+    }
+  }
 
   // Create an UnwindHelp object.
   // The UnwindHelp object is allocated at the start of the fixed object area
-  int64_t FixedObject =
-      getFixedObjectSize(MF, AFI, /*IsWin64*/ true, /*IsFunclet*/ false);
-  int UnwindHelpFI = MFI.CreateFixedObject(/*Size*/ 8,
-                                           /*SPOffset*/ -FixedObject,
+  int64_t UnwindHelpOffset = alignTo(CurrentOffset + 8, Align(16));
+  assert(UnwindHelpOffset == getFixedObjectSize(MF, AFI, /*IsWin64*/ true,
+                                                /*IsFunclet*/ false) &&
+         "UnwindHelpOffset must be at the start of the fixed object area");
+  int UnwindHelpFI = MFI.CreateFixedObject(/*Size*/ 8, -UnwindHelpOffset,
                                            /*IsImmutable=*/false);
   EHInfo.UnwindHelpFrameIdx = UnwindHelpFI;
 
+  MachineBasicBlock &MBB = MF.front();
+  auto MBBI = MBB.begin();
+  while (MBBI != MBB.end() && MBBI->getFlag(MachineInstr::FrameSetup))
+    ++MBBI;
+
   // We need to store -2 into the UnwindHelp object at the start of the
   // function.
   DebugLoc DL;
   RS->enterBasicBlockEnd(MBB);
   RS->backward(MBBI);
   Register DstReg = RS->FindUnusedReg(&AArch64::GPR64commonRegClass);
   assert(DstReg && "There must be a free register after frame setup");
+  const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
   BuildMI(MBB, MBBI, DL, TII.get(AArch64::MOVi64imm), DstReg).addImm(-2);
   BuildMI(MBB, MBBI, DL, TII.get(AArch64::STURXi))
       .addReg(DstReg, getKillRegState(true))

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -28237,9 +28237,7 @@ void AArch64TargetLowering::finalizeLowering(MachineFunction &MF) const {
 }
 
 // Unlike X86, we let frame lowering assign offsets to all catch objects.
-bool AArch64TargetLowering::needsFixedCatchObjects() const {
-  return false;
-}
+bool AArch64TargetLowering::needsFixedCatchObjects() const { return true; }
 
 bool AArch64TargetLowering::shouldLocalize(
     const MachineInstr &MI, const TargetTransformInfo *TTI) const {

diff --git a/llvm/test/CodeGen/AArch64/wineh-aligned-stack-obj.ll b/llvm/test/CodeGen/AArch64/wineh-aligned-stack-obj.ll
@@ -0,0 +1,145 @@
+; RUN: llc %s --mtriple=aarch64-pc-windows-msvc -o - | FileCheck %s
+
+; Regression test for handling MSVC C++ exceptions when there's an aligned
+; object on the stack.
+
+; Generated from this C++ code:
+; https://godbolt.org/z/cGzGfqq34
+; > clang --target=aarch64-pc-windows-msvc test.cpp
+; ```
+; // Large object: alignment seems to be important?
+; struct alignas(128) BigObj {
+;     int value;
+;     // Destructor so it's kept alive.
+;     ~BigObj() { }
+; };
+;
+; // Exception type need to be large enough to not fit in a register.
+; struct Error {
+;     int value;
+;     int padding[3];
+; };
+;
+; int main() {
+;     BigObj bo{};
+;
+;     try {
+;         throw Error { 42, {0, 0, 0} };
+;     } catch (const Error& e) {
+;         return e.value;
+;     }
+;     return 0;
+; }
+; ```
+
+; CHECK-LABEL:  main:
+; CHECK:        sub x[[SPTMP:[0-9]+]], sp, #336
+; CHECK:        and sp, x[[SPTMP]], #0xffffffffffffff80
+; CHECK:        mov x[[FP:[0-9]+]], sp
+; CHECK:        str wzr, [x[[FP]], #332]
+
+; CHECK-LABEL:  "?catch$3@?0?main@4HA":
+; CHECK:        str	w8, [x[[FP]], #332]
+; CHECK-NEXT:   .seh_startepilogue
+; CHECK:        ret
+
+; CHECK-LABEL:  $cppxdata$main:
+; CHECK:        .word   -16                             // UnwindHelp
+; CHECK-LABEL:  $handlerMap$0$main:
+; CHECK-NEXT:   .word   8                               // Adjectives
+; CHECK-NEXT:   .word   "??_R0?AUError@@@8"@IMGREL      // Type
+; CHECK-NEXT:   .word   -8                              // CatchObjOffset
+; CHECK-NEXT:   .word   "?catch$3@?0?main@4HA"@IMGREL   // Handler
+
+%rtti.TypeDescriptor11 = type { ptr, ptr, [12 x i8] }
+%eh.CatchableType = type { i32, i32, i32, i32, i32, i32, i32 }
+%eh.CatchableTypeArray.1 = type { i32, [1 x i32] }
+%eh.ThrowInfo = type { i32, i32, i32, i32 }
+%struct.BigObj = type { i32, [124 x i8] }
+%struct.Error = type { i32, [3 x i32] }
+
+$"??1BigObj@@QEAA@XZ" = comdat any
+
+$"??_R0?AUError@@@8" = comdat any
+
+$"_CT??_R0?AUError@@@816" = comdat any
+
+$"_CTA1?AUError@@" = comdat any
+
+$"_TI1?AUError@@" = comdat any
+
+@"??_7type_info@@6B@" = external constant ptr
+@"??_R0?AUError@@@8" = linkonce_odr global %rtti.TypeDescriptor11 { ptr @"??_7type_info@@6B@", ptr null, [12 x i8] c".?AUError@@\00" }, comdat
+@__ImageBase = external dso_local constant i8
+@"_CT??_R0?AUError@@@816" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (ptr @"??_R0?AUError@@@8" to i64), i64 ptrtoint (ptr @__ImageBase to i64)) to i32), i32 0, i32 -1, i32 0, i32 16, i32 0 }, section ".xdata", comdat
+@"_CTA1?AUError@@" = linkonce_odr unnamed_addr constant %eh.CatchableTypeArray.1 { i32 1, [1 x i32] [i32 trunc (i64 sub nuw nsw (i64 ptrtoint (ptr @"_CT??_R0?AUError@@@816" to i64), i64 ptrtoint (ptr @__ImageBase to i64)) to i32)] }, section ".xdata", comdat
+@"_TI1?AUError@@" = linkonce_odr unnamed_addr constant %eh.ThrowInfo { i32 0, i32 0, i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (ptr @"_CTA1?AUError@@" to i64), i64 ptrtoint (ptr @__ImageBase to i64)) to i32) }, section ".xdata", comdat
+
+define dso_local noundef i32 @main() personality ptr @__CxxFrameHandler3 {
+entry:
+  %retval = alloca i32, align 4
+  %bo = alloca %struct.BigObj, align 128
+  %tmp = alloca %struct.Error, align 4
+  %e = alloca ptr, align 8
+  %cleanup.dest.slot = alloca i32, align 4
+  store i32 0, ptr %retval, align 4
+  call void @llvm.memset.p0.i64(ptr align 128 %bo, i8 0, i64 128, i1 false)
+  %value = getelementptr inbounds nuw %struct.BigObj, ptr %bo, i32 0, i32 0
+  %value1 = getelementptr inbounds nuw %struct.Error, ptr %tmp, i32 0, i32 0
+  store i32 42, ptr %value1, align 4
+  %padding = getelementptr inbounds nuw %struct.Error, ptr %tmp, i32 0, i32 1
+  store i32 0, ptr %padding, align 4
+  %arrayinit.element = getelementptr inbounds i32, ptr %padding, i64 1
+  store i32 0, ptr %arrayinit.element, align 4
+  %arrayinit.element2 = getelementptr inbounds i32, ptr %padding, i64 2
+  store i32 0, ptr %arrayinit.element2, align 4
+  invoke void @_CxxThrowException(ptr %tmp, ptr @"_TI1?AUError@@") #3
+          to label %unreachable unwind label %catch.dispatch
+
+catch.dispatch:
+  %0 = catchswitch within none [label %catch] unwind label %ehcleanup
+
+catch:
+  %1 = catchpad within %0 [ptr @"??_R0?AUError@@@8", i32 8, ptr %e]
+  %2 = load ptr, ptr %e, align 8
+  %value3 = getelementptr inbounds nuw %struct.Error, ptr %2, i32 0, i32 0
+  %3 = load i32, ptr %value3, align 4
+  store i32 %3, ptr %retval, align 4
+  store i32 1, ptr %cleanup.dest.slot, align 4
+  catchret from %1 to label %catchret.dest
+
+catchret.dest:
+  br label %cleanup
+
+try.cont:
+  store i32 0, ptr %retval, align 4
+  store i32 1, ptr %cleanup.dest.slot, align 4
+  br label %cleanup
+
+cleanup:
+  call void @"??1BigObj@@QEAA@XZ"(ptr noundef nonnull align 128 dereferenceable(4) %bo) #4
+  %4 = load i32, ptr %retval, align 4
+  ret i32 %4
+
+ehcleanup:
+  %5 = cleanuppad within none []
+  call void @"??1BigObj@@QEAA@XZ"(ptr noundef nonnull align 128 dereferenceable(4) %bo) [ "funclet"(token %5) ]
+  cleanupret from %5 unwind to caller
+
+unreachable:
+  unreachable
+}
+
+declare void @llvm.memset.p0.i64(ptr writeonly captures(none), i8, i64, i1 immarg) #1
+
+declare dso_local void @_CxxThrowException(ptr, ptr)
+
+declare dso_local i32 @__CxxFrameHandler3(...)
+
+define linkonce_odr dso_local void @"??1BigObj@@QEAA@XZ"(ptr noundef nonnull align 128 dereferenceable(4) %this) unnamed_addr comdat {
+entry:
+  %this.addr = alloca ptr, align 8
+  store ptr %this, ptr %this.addr, align 8
+  %this1 = load ptr, ptr %this.addr, align 8
+  ret void
+}
diff --git a/llvm/test/CodeGen/AArch64/wineh-try-catch.ll b/llvm/test/CodeGen/AArch64/wineh-try-catch.ll
@@ -20,7 +20,7 @@
 ; CHECK:       str     x28, [sp, #24]
 ; CHECK:       stp     x29, x30, [sp, #32]
 ; CHECK:       add     x29, sp, #32
-; CHECK:       sub     sp, sp, #624
+; CHECK:       sub     sp, sp, #608
 ; CHECK:       mov     x19, sp
 ; CHECK:       mov     x0, #-2
 ; CHECK:       stur    x0, [x29, #16]
@@ -51,7 +51,7 @@
 ; CHECK:       str     x21, [sp, #16]
 ; CHECK:       str     x28, [sp, #24]
 ; CHECK:       stp     x29, x30, [sp, #32]
-; CHECK:       add     x20, x19, #12
+; CHECK:       add     x20, x19, #0
 
 ; Check that there are no further stack updates.
 ; CHECK-NOT:   sub     sp, sp