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fe4a3fd086
Otherwise, the Win64 unwinder considers direct branches to such empty trailing BBs to be a branch out of the function. It treats such a branch as a tail call, which can only be part of an epilogue. If the unwinder misclassifies such a branch as part of the epilogue, it will fail to unwind the stack further. This can lead to bad stack traces, or failure to handle exceptions properly. This is described in https://llvm.org/PR45064#c4, and by the comment at the top of the X86AvoidTrailingCallPass.cpp file. It should be safe to insert int3 for such blocks. An empty trailing BB that reaches this pass is pretty much guaranteed to be unreachable. If a program executed such a block, it would fall off the end of the function. Most of the complexity in this patch comes from threading through the "EHFuncletEntry" boolean on the MIRParser and registering the pass so we can stop and start codegen around it. I used an MIR test because we should teach LLVM to optimize away these branches as a follow-up. Reviewed By: hans Differential Revision: https://reviews.llvm.org/D76531
224 lines
7.3 KiB
YAML
224 lines
7.3 KiB
YAML
# RUN: llc -start-before=x86-avoid-trailing-call %s -o - | FileCheck %s
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# If there is a trailing unreachable block, make sure it is non-empty.
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# Manually modified the IR of the following C++ to share one unreachable block,
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# as clang does for the real C++ throw:
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# void __declspec(noreturn) mythrow();
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# int multi_throw(bool c1, bool c2, bool c3) {
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# try {
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# if (c1)
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# mythrow();
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# if (c2)
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# mythrow();
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# if (c3)
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# mythrow();
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# } catch (...) {
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# return 1;
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# }
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# return 0;
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# }
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# CHECK-LABEL: "?multi_throw@@YAH_N00@Z": # @"?multi_throw@@YAH_N00@Z"
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# CHECK: retq
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# CHECK: .LBB{{.*}} # %if.then
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# CHECK: callq mythrow
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# CHECK: .LBB{{.*}} # %if.then4
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# CHECK: callq mythrow
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# CHECK: .LBB{{.*}} # %if.then8
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# CHECK: callq mythrow
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# CHECK: .LBB{{.*}} # %unreachable
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# CHECK-NEXT: int3
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# CHECK: .seh_endproc
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# CHECK: # %catch
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--- |
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; ModuleID = '../llvm/test/CodeGen/X86/win64-eh-empty-block-2.ll'
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source_filename = "t.cpp"
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target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-windows-msvc19.11.0"
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; Function Attrs: uwtable
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define dso_local i32 @"?multi_throw@@YAH_N00@Z"(i1 zeroext %c1, i1 zeroext %c2, i1 zeroext %c3) local_unnamed_addr #0 personality i8* bitcast (i32 (...)* @__CxxFrameHandler3 to i8*) {
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entry:
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br i1 %c1, label %if.then, label %if.end
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if.then: ; preds = %entry
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invoke void @mythrow()
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to label %unreachable unwind label %catch.dispatch
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unreachable: ; preds = %if.then8, %if.then4, %if.then
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unreachable
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if.end: ; preds = %entry
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br i1 %c2, label %if.then4, label %if.end6
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if.then4: ; preds = %if.end
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invoke void @mythrow()
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to label %unreachable unwind label %catch.dispatch
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if.end6: ; preds = %if.end
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br i1 %c3, label %if.then8, label %return
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if.then8: ; preds = %if.end6
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invoke void @mythrow()
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to label %unreachable unwind label %catch.dispatch
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catch.dispatch: ; preds = %if.then8, %if.then4, %if.then
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%0 = catchswitch within none [label %catch] unwind to caller
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catch: ; preds = %catch.dispatch
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%1 = catchpad within %0 [i8* null, i32 64, i8* null]
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catchret from %1 to label %return
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return: ; preds = %catch, %if.end6
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%retval.0 = phi i32 [ 1, %catch ], [ 0, %if.end6 ]
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ret i32 %retval.0
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}
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declare dso_local void @mythrow()
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declare dso_local i32 @__CxxFrameHandler3(...)
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attributes #0 = { uwtable }
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!llvm.module.flags = !{!0, !1}
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!0 = !{i32 1, !"wchar_size", i32 2}
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!1 = !{i32 7, !"PIC Level", i32 2}
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...
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---
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name: '?multi_throw@@YAH_N00@Z'
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alignment: 16
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exposesReturnsTwice: false
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legalized: false
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regBankSelected: false
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selected: false
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failedISel: false
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tracksRegLiveness: true
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hasWinCFI: true
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registers: []
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liveins:
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- { reg: '$cl', virtual-reg: '' }
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- { reg: '$dl', virtual-reg: '' }
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- { reg: '$r8b', virtual-reg: '' }
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frameInfo:
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isFrameAddressTaken: false
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isReturnAddressTaken: false
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hasStackMap: false
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hasPatchPoint: false
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stackSize: 56
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offsetAdjustment: -56
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maxAlignment: 8
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adjustsStack: true
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hasCalls: true
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stackProtector: ''
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maxCallFrameSize: 32
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cvBytesOfCalleeSavedRegisters: 0
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hasOpaqueSPAdjustment: true
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hasVAStart: false
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hasMustTailInVarArgFunc: false
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localFrameSize: 0
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savePoint: ''
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restorePoint: ''
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fixedStack:
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- { id: 0, type: default, offset: -24, size: 8, alignment: 8, stack-id: default,
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isImmutable: false, isAliased: false, callee-saved-register: '',
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callee-saved-restored: true, debug-info-variable: '', debug-info-expression: '',
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debug-info-location: '' }
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- { id: 1, type: spill-slot, offset: -16, size: 8, alignment: 16, stack-id: default,
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callee-saved-register: '', callee-saved-restored: true, debug-info-variable: '',
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debug-info-expression: '', debug-info-location: '' }
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stack:
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- { id: 0, name: '', type: spill-slot, offset: -28, size: 4, alignment: 4,
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stack-id: default, callee-saved-register: '', callee-saved-restored: true,
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debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
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callSites: []
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constants: []
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machineFunctionInfo: {}
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body: |
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bb.0.entry:
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successors: %bb.1(0x00000001), %bb.3(0x7fffffff)
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liveins: $cl, $dl, $r8b
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frame-setup PUSH64r killed $rbp, implicit-def $rsp, implicit $rsp
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frame-setup SEH_PushReg 50
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$rsp = frame-setup SUB64ri8 $rsp, 48, implicit-def dead $eflags
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frame-setup SEH_StackAlloc 48
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$rbp = LEA64r $rsp, 1, $noreg, 48, $noreg
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frame-setup SEH_SetFrame 50, 48
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frame-setup SEH_EndPrologue
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MOV64mi32 $rbp, 1, $noreg, -8, $noreg, -2 :: (store 8 into %fixed-stack.0)
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TEST8rr killed renamable $cl, renamable $cl, implicit-def $eflags
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JCC_1 %bb.1, 5, implicit $eflags
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bb.3.if.end:
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successors: %bb.4(0x00000001), %bb.5(0x7fffffff)
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liveins: $dl, $r8b
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TEST8rr killed renamable $dl, renamable $dl, implicit-def $eflags
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JCC_1 %bb.4, 5, implicit $eflags
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bb.5.if.end6:
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successors: %bb.6(0x00000001), %bb.8(0x7fffffff)
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liveins: $r8b
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MOV32mi $rbp, 1, $noreg, -12, $noreg, 0 :: (store 4 into %stack.0)
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TEST8rr killed renamable $r8b, renamable $r8b, implicit-def $eflags
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JCC_1 %bb.6, 5, implicit $eflags
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bb.8.return (address-taken):
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$eax = MOV32rm $rbp, 1, $noreg, -12, $noreg :: (load 4 from %stack.0)
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SEH_Epilogue
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$rsp = frame-destroy ADD64ri8 $rsp, 48, implicit-def dead $eflags
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$rbp = frame-destroy POP64r implicit-def $rsp, implicit $rsp
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RETQ $eax
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bb.1.if.then:
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successors: %bb.2(0x7ffff800), %bb.7(0x00000800)
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EH_LABEL <mcsymbol .Leh1>
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CALL64pcrel32 @mythrow, csr_win64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp
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EH_LABEL <mcsymbol .Leh2>
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JMP_1 %bb.2
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bb.4.if.then4:
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successors: %bb.2(0x7ffff800), %bb.7(0x00000800)
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EH_LABEL <mcsymbol .Leh3>
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CALL64pcrel32 @mythrow, csr_win64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp
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EH_LABEL <mcsymbol .Leh4>
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JMP_1 %bb.2
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bb.6.if.then8:
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successors: %bb.2(0x7ffff800), %bb.7(0x00000800)
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EH_LABEL <mcsymbol .Leh5>
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CALL64pcrel32 @mythrow, csr_win64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp
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EH_LABEL <mcsymbol .Leh6>
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bb.2.unreachable:
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successors:
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bb.7.catch (landing-pad, ehfunclet-entry):
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successors: %bb.8(0x80000000)
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liveins: $rdx
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frame-setup MOV64mr killed $rsp, 1, $noreg, 16, $noreg, $rdx
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frame-setup PUSH64r killed $rbp, implicit-def $rsp, implicit $rsp
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frame-setup SEH_PushReg 50
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$rsp = frame-setup SUB64ri8 $rsp, 32, implicit-def dead $eflags
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frame-setup SEH_StackAlloc 32
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$rbp = LEA64r $rdx, 1, $noreg, 48, $noreg
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frame-setup SEH_EndPrologue
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MOV32mi $rbp, 1, $noreg, -12, $noreg, 1 :: (store 4 into %stack.0)
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$rax = LEA64r $rip, 0, $noreg, %bb.8, $noreg
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SEH_Epilogue
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$rsp = frame-destroy ADD64ri8 $rsp, 32, implicit-def dead $eflags
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$rbp = frame-destroy POP64r implicit-def $rsp, implicit $rsp
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CATCHRET %bb.8, %bb.0
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...
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