[llvm] r238402 - [ASan] New approach to dynamic allocas unpoisoning. Patch by Max Ostapenko!
Yury Gribov
y.gribov at samsung.com
Thu May 28 00:51:50 PDT 2015
Author: ygribov
Date: Thu May 28 02:51:49 2015
New Revision: 238402
URL: http://llvm.org/viewvc/llvm-project?rev=238402&view=rev
Log:
[ASan] New approach to dynamic allocas unpoisoning. Patch by Max Ostapenko!
Differential Revision: http://reviews.llvm.org/D7098
Removed:
llvm/trunk/test/Instrumentation/AddressSanitizer/undecidable-dynamic-alloca-1.ll
Modified:
llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
llvm/trunk/test/Instrumentation/AddressSanitizer/instrument-dynamic-allocas.ll
Modified: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp?rev=238402&r1=238401&r2=238402&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp Thu May 28 02:51:49 2015
@@ -106,14 +106,15 @@ static const char *const kAsanUnpoisonSt
static const char *const kAsanOptionDetectUAR =
"__asan_option_detect_stack_use_after_return";
+static const char *const kAsanAllocaPoison =
+ "__asan_alloca_poison";
+static const char *const kAsanAllocasUnpoison =
+ "__asan_allocas_unpoison";
+
// Accesses sizes are powers of two: 1, 2, 4, 8, 16.
static const size_t kNumberOfAccessSizes = 5;
static const unsigned kAllocaRzSize = 32;
-static const unsigned kAsanAllocaLeftMagic = 0xcacacacaU;
-static const unsigned kAsanAllocaRightMagic = 0xcbcbcbcbU;
-static const unsigned kAsanAllocaPartialVal1 = 0xcbcbcb00U;
-static const unsigned kAsanAllocaPartialVal2 = 0x000000cbU;
// Command-line flags.
@@ -230,8 +231,6 @@ static cl::opt<int> ClDebugMax("asan-deb
STATISTIC(NumInstrumentedReads, "Number of instrumented reads");
STATISTIC(NumInstrumentedWrites, "Number of instrumented writes");
-STATISTIC(NumInstrumentedDynamicAllocas,
- "Number of instrumented dynamic allocas");
STATISTIC(NumOptimizedAccessesToGlobalVar,
"Number of optimized accesses to global vars");
STATISTIC(NumOptimizedAccessesToStackVar,
@@ -402,6 +401,12 @@ struct AddressSanitizer : public Functio
}
/// Check if we want (and can) handle this alloca.
bool isInterestingAlloca(AllocaInst &AI);
+
+ // Check if we have dynamic alloca.
+ bool isDynamicAlloca(AllocaInst &AI) const {
+ return AI.isArrayAllocation() || !AI.isStaticAlloca();
+ }
+
/// If it is an interesting memory access, return the PointerOperand
/// and set IsWrite/Alignment. Otherwise return nullptr.
Value *isInterestingMemoryAccess(Instruction *I, bool *IsWrite,
@@ -517,6 +522,7 @@ struct FunctionStackPoisoner : public In
Function *AsanStackMallocFunc[kMaxAsanStackMallocSizeClass + 1],
*AsanStackFreeFunc[kMaxAsanStackMallocSizeClass + 1];
Function *AsanPoisonStackMemoryFunc, *AsanUnpoisonStackMemoryFunc;
+ Function *AsanAllocaPoisonFunc, *AsanAllocasUnpoisonFunc;
// Stores a place and arguments of poisoning/unpoisoning call for alloca.
struct AllocaPoisonCall {
@@ -527,23 +533,9 @@ struct FunctionStackPoisoner : public In
};
SmallVector<AllocaPoisonCall, 8> AllocaPoisonCallVec;
- // Stores left and right redzone shadow addresses for dynamic alloca
- // and pointer to alloca instruction itself.
- // LeftRzAddr is a shadow address for alloca left redzone.
- // RightRzAddr is a shadow address for alloca right redzone.
- struct DynamicAllocaCall {
- AllocaInst *AI;
- Value *LeftRzAddr;
- Value *RightRzAddr;
- bool Poison;
- explicit DynamicAllocaCall(AllocaInst *AI, Value *LeftRzAddr = nullptr,
- Value *RightRzAddr = nullptr)
- : AI(AI),
- LeftRzAddr(LeftRzAddr),
- RightRzAddr(RightRzAddr),
- Poison(true) {}
- };
- SmallVector<DynamicAllocaCall, 1> DynamicAllocaVec;
+ SmallVector<AllocaInst *, 1> DynamicAllocaVec;
+ SmallVector<IntrinsicInst *, 1> StackRestoreVec;
+ AllocaInst *DynamicAllocaLayout = nullptr;
// Maps Value to an AllocaInst from which the Value is originated.
typedef DenseMap<Value *, AllocaInst *> AllocaForValueMapTy;
@@ -586,42 +578,30 @@ struct FunctionStackPoisoner : public In
// Then unpoison everything back before the function returns.
void poisonStack();
+ void createDynamicAllocasInitStorage();
+
// ----------------------- Visitors.
/// \brief Collect all Ret instructions.
void visitReturnInst(ReturnInst &RI) { RetVec.push_back(&RI); }
- // Unpoison dynamic allocas redzones.
- void unpoisonDynamicAlloca(DynamicAllocaCall &AllocaCall) {
- if (!AllocaCall.Poison) return;
- for (auto Ret : RetVec) {
- IRBuilder<> IRBRet(Ret);
- PointerType *Int32PtrTy = PointerType::getUnqual(IRBRet.getInt32Ty());
- Value *Zero = Constant::getNullValue(IRBRet.getInt32Ty());
- Value *PartialRzAddr = IRBRet.CreateSub(AllocaCall.RightRzAddr,
- ConstantInt::get(IntptrTy, 4));
- IRBRet.CreateStore(
- Zero, IRBRet.CreateIntToPtr(AllocaCall.LeftRzAddr, Int32PtrTy));
- IRBRet.CreateStore(Zero,
- IRBRet.CreateIntToPtr(PartialRzAddr, Int32PtrTy));
- IRBRet.CreateStore(
- Zero, IRBRet.CreateIntToPtr(AllocaCall.RightRzAddr, Int32PtrTy));
- }
+ void unpoisonDynamicAllocasBeforeInst(Instruction *InstBefore,
+ Value *SavedStack) {
+ IRBuilder<> IRB(InstBefore);
+ IRB.CreateCall2(AsanAllocasUnpoisonFunc,
+ IRB.CreateLoad(DynamicAllocaLayout),
+ IRB.CreatePtrToInt(SavedStack, IntptrTy));
}
- // Right shift for BigEndian and left shift for LittleEndian.
- Value *shiftAllocaMagic(Value *Val, IRBuilder<> &IRB, Value *Shift) {
- auto &DL = F.getParent()->getDataLayout();
- return DL.isLittleEndian() ? IRB.CreateShl(Val, Shift)
- : IRB.CreateLShr(Val, Shift);
+ // Unpoison dynamic allocas redzones.
+ void unpoisonDynamicAllocas() {
+ for (auto &Ret : RetVec)
+ unpoisonDynamicAllocasBeforeInst(Ret, DynamicAllocaLayout);
+
+ for (auto &StackRestoreInst : StackRestoreVec)
+ unpoisonDynamicAllocasBeforeInst(StackRestoreInst,
+ StackRestoreInst->getOperand(0));
}
- // Compute PartialRzMagic for dynamic alloca call. Since we don't know the
- // size of requested memory until runtime, we should compute it dynamically.
- // If PartialSize is 0, PartialRzMagic would contain kAsanAllocaRightMagic,
- // otherwise it would contain the value that we will use to poison the
- // partial redzone for alloca call.
- Value *computePartialRzMagic(Value *PartialSize, IRBuilder<> &IRB);
-
// Deploy and poison redzones around dynamic alloca call. To do this, we
// should replace this call with another one with changed parameters and
// replace all its uses with new address, so
@@ -632,20 +612,15 @@ struct FunctionStackPoisoner : public In
// addr = tmp + 32 (first 32 bytes are for the left redzone).
// Additional_size is added to make new memory allocation contain not only
// requested memory, but also left, partial and right redzones.
- // After that, we should poison redzones:
- // (1) Left redzone with kAsanAllocaLeftMagic.
- // (2) Partial redzone with the value, computed in runtime by
- // computePartialRzMagic function.
- // (3) Right redzone with kAsanAllocaRightMagic.
- void handleDynamicAllocaCall(DynamicAllocaCall &AllocaCall);
+ void handleDynamicAllocaCall(AllocaInst *AI);
/// \brief Collect Alloca instructions we want (and can) handle.
void visitAllocaInst(AllocaInst &AI) {
if (!ASan.isInterestingAlloca(AI)) return;
StackAlignment = std::max(StackAlignment, AI.getAlignment());
- if (isDynamicAlloca(AI))
- DynamicAllocaVec.push_back(DynamicAllocaCall(&AI));
+ if (ASan.isDynamicAlloca(AI))
+ DynamicAllocaVec.push_back(&AI);
else
AllocaVec.push_back(&AI);
}
@@ -653,8 +628,9 @@ struct FunctionStackPoisoner : public In
/// \brief Collect lifetime intrinsic calls to check for use-after-scope
/// errors.
void visitIntrinsicInst(IntrinsicInst &II) {
- if (!ClCheckLifetime) return;
Intrinsic::ID ID = II.getIntrinsicID();
+ if (ID == Intrinsic::stackrestore) StackRestoreVec.push_back(&II);
+ if (!ClCheckLifetime) return;
if (ID != Intrinsic::lifetime_start && ID != Intrinsic::lifetime_end)
return;
// Found lifetime intrinsic, add ASan instrumentation if necessary.
@@ -690,9 +666,6 @@ struct FunctionStackPoisoner : public In
return true;
}
- bool isDynamicAlloca(AllocaInst &AI) const {
- return AI.isArrayAllocation() || !AI.isStaticAlloca();
- }
/// Finds alloca where the value comes from.
AllocaInst *findAllocaForValue(Value *V);
void poisonRedZones(ArrayRef<uint8_t> ShadowBytes, IRBuilder<> &IRB,
@@ -811,12 +784,14 @@ bool AddressSanitizer::isInterestingAllo
if (PreviouslySeenAllocaInfo != ProcessedAllocas.end())
return PreviouslySeenAllocaInfo->getSecond();
- bool IsInteresting = (AI.getAllocatedType()->isSized() &&
- // alloca() may be called with 0 size, ignore it.
- getAllocaSizeInBytes(&AI) > 0 &&
- // We are only interested in allocas not promotable to registers.
- // Promotable allocas are common under -O0.
- (!ClSkipPromotableAllocas || !isAllocaPromotable(&AI)));
+ bool IsInteresting =
+ (AI.getAllocatedType()->isSized() &&
+ // alloca() may be called with 0 size, ignore it.
+ getAllocaSizeInBytes(&AI) > 0 &&
+ // We are only interested in allocas not promotable to registers.
+ // Promotable allocas are common under -O0.
+ (!ClSkipPromotableAllocas || !isAllocaPromotable(&AI) ||
+ isDynamicAlloca(AI)));
ProcessedAllocas[&AI] = IsInteresting;
return IsInteresting;
@@ -1617,6 +1592,11 @@ void FunctionStackPoisoner::initializeCa
AsanUnpoisonStackMemoryFunc = checkSanitizerInterfaceFunction(
M.getOrInsertFunction(kAsanUnpoisonStackMemoryName, IRB.getVoidTy(),
IntptrTy, IntptrTy, nullptr));
+ AsanAllocaPoisonFunc = checkSanitizerInterfaceFunction(M.getOrInsertFunction(
+ kAsanAllocaPoison, IRB.getVoidTy(), IntptrTy, IntptrTy, nullptr));
+ AsanAllocasUnpoisonFunc =
+ checkSanitizerInterfaceFunction(M.getOrInsertFunction(
+ kAsanAllocasUnpoison, IRB.getVoidTy(), IntptrTy, IntptrTy, nullptr));
}
void FunctionStackPoisoner::poisonRedZones(ArrayRef<uint8_t> ShadowBytes,
@@ -1712,15 +1692,24 @@ Value *FunctionStackPoisoner::createAllo
return IRB.CreatePointerCast(Alloca, IntptrTy);
}
+void FunctionStackPoisoner::createDynamicAllocasInitStorage() {
+ BasicBlock &FirstBB = *F.begin();
+ IRBuilder<> IRB(dyn_cast<Instruction>(FirstBB.begin()));
+ DynamicAllocaLayout = IRB.CreateAlloca(IntptrTy, nullptr);
+ IRB.CreateStore(Constant::getNullValue(IntptrTy), DynamicAllocaLayout);
+ DynamicAllocaLayout->setAlignment(32);
+}
+
void FunctionStackPoisoner::poisonStack() {
assert(AllocaVec.size() > 0 || DynamicAllocaVec.size() > 0);
- if (ClInstrumentAllocas) {
+ if (ClInstrumentAllocas && DynamicAllocaVec.size() > 0) {
// Handle dynamic allocas.
- for (auto &AllocaCall : DynamicAllocaVec) {
- handleDynamicAllocaCall(AllocaCall);
- unpoisonDynamicAlloca(AllocaCall);
- }
+ createDynamicAllocasInitStorage();
+ for (auto &AI : DynamicAllocaVec)
+ handleDynamicAllocaCall(AI);
+
+ unpoisonDynamicAllocas();
}
if (AllocaVec.size() == 0) return;
@@ -1955,78 +1944,25 @@ AllocaInst *FunctionStackPoisoner::findA
return Res;
}
-// Compute PartialRzMagic for dynamic alloca call. PartialRzMagic is
-// constructed from two separate 32-bit numbers: PartialRzMagic = Val1 | Val2.
-// (1) Val1 is resposible for forming base value for PartialRzMagic, containing
-// only 00 for fully addressable and 0xcb for fully poisoned bytes for each
-// 8-byte chunk of user memory respectively.
-// (2) Val2 forms the value for marking first poisoned byte in shadow memory
-// with appropriate value (0x01 - 0x07 or 0xcb if Padding % 8 == 0).
-
-// Shift = Padding & ~7; // the number of bits we need to shift to access first
-// chunk in shadow memory, containing nonzero bytes.
-// Example:
-// Padding = 21 Padding = 16
-// Shadow: |00|00|05|cb| Shadow: |00|00|cb|cb|
-// ^ ^
-// | |
-// Shift = 21 & ~7 = 16 Shift = 16 & ~7 = 16
-//
-// Val1 = 0xcbcbcbcb << Shift;
-// PartialBits = Padding ? Padding & 7 : 0xcb;
-// Val2 = PartialBits << Shift;
-// Result = Val1 | Val2;
-Value *FunctionStackPoisoner::computePartialRzMagic(Value *PartialSize,
- IRBuilder<> &IRB) {
- PartialSize = IRB.CreateIntCast(PartialSize, IRB.getInt32Ty(), false);
- Value *Shift = IRB.CreateAnd(PartialSize, IRB.getInt32(~7));
- unsigned Val1Int = kAsanAllocaPartialVal1;
- unsigned Val2Int = kAsanAllocaPartialVal2;
- if (!F.getParent()->getDataLayout().isLittleEndian()) {
- Val1Int = sys::getSwappedBytes(Val1Int);
- Val2Int = sys::getSwappedBytes(Val2Int);
- }
- Value *Val1 = shiftAllocaMagic(IRB.getInt32(Val1Int), IRB, Shift);
- Value *PartialBits = IRB.CreateAnd(PartialSize, IRB.getInt32(7));
- // For BigEndian get 0x000000YZ -> 0xYZ000000.
- if (F.getParent()->getDataLayout().isBigEndian())
- PartialBits = IRB.CreateShl(PartialBits, IRB.getInt32(24));
- Value *Val2 = IRB.getInt32(Val2Int);
- Value *Cond =
- IRB.CreateICmpNE(PartialBits, Constant::getNullValue(IRB.getInt32Ty()));
- Val2 = IRB.CreateSelect(Cond, shiftAllocaMagic(PartialBits, IRB, Shift),
- shiftAllocaMagic(Val2, IRB, Shift));
- return IRB.CreateOr(Val1, Val2);
-}
-
-void FunctionStackPoisoner::handleDynamicAllocaCall(
- DynamicAllocaCall &AllocaCall) {
- AllocaInst *AI = AllocaCall.AI;
- if (!doesDominateAllExits(AI)) {
- // We do not yet handle complex allocas
- AllocaCall.Poison = false;
- return;
- }
-
+void FunctionStackPoisoner::handleDynamicAllocaCall(AllocaInst *AI) {
IRBuilder<> IRB(AI);
- PointerType *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
const unsigned Align = std::max(kAllocaRzSize, AI->getAlignment());
const uint64_t AllocaRedzoneMask = kAllocaRzSize - 1;
Value *Zero = Constant::getNullValue(IntptrTy);
Value *AllocaRzSize = ConstantInt::get(IntptrTy, kAllocaRzSize);
Value *AllocaRzMask = ConstantInt::get(IntptrTy, AllocaRedzoneMask);
- Value *NotAllocaRzMask = ConstantInt::get(IntptrTy, ~AllocaRedzoneMask);
// Since we need to extend alloca with additional memory to locate
// redzones, and OldSize is number of allocated blocks with
// ElementSize size, get allocated memory size in bytes by
// OldSize * ElementSize.
- unsigned ElementSize =
+ const unsigned ElementSize =
F.getParent()->getDataLayout().getTypeAllocSize(AI->getAllocatedType());
- Value *OldSize = IRB.CreateMul(AI->getArraySize(),
- ConstantInt::get(IntptrTy, ElementSize));
+ Value *OldSize =
+ IRB.CreateMul(IRB.CreateIntCast(AI->getArraySize(), IntptrTy, false),
+ ConstantInt::get(IntptrTy, ElementSize));
// PartialSize = OldSize % 32
Value *PartialSize = IRB.CreateAnd(OldSize, AllocaRzMask);
@@ -2054,43 +1990,20 @@ void FunctionStackPoisoner::handleDynami
Value *NewAddress = IRB.CreateAdd(IRB.CreatePtrToInt(NewAlloca, IntptrTy),
ConstantInt::get(IntptrTy, Align));
- Value *NewAddressPtr = IRB.CreateIntToPtr(NewAddress, AI->getType());
+ // Insert __asan_alloca_poison call for new created alloca.
+ IRB.CreateCall2(AsanAllocaPoisonFunc, NewAddress, OldSize);
- // LeftRzAddress = NewAddress - kAllocaRzSize
- Value *LeftRzAddress = IRB.CreateSub(NewAddress, AllocaRzSize);
+ // Store the last alloca's address to DynamicAllocaLayout. We'll need this
+ // for unpoisoning stuff.
+ IRB.CreateStore(IRB.CreatePtrToInt(NewAlloca, IntptrTy), DynamicAllocaLayout);
- // Poisoning left redzone.
- AllocaCall.LeftRzAddr = ASan.memToShadow(LeftRzAddress, IRB);
- IRB.CreateStore(ConstantInt::get(IRB.getInt32Ty(), kAsanAllocaLeftMagic),
- IRB.CreateIntToPtr(AllocaCall.LeftRzAddr, Int32PtrTy));
-
- // PartialRzAligned = PartialRzAddr & ~AllocaRzMask
- Value *PartialRzAddr = IRB.CreateAdd(NewAddress, OldSize);
- Value *PartialRzAligned = IRB.CreateAnd(PartialRzAddr, NotAllocaRzMask);
-
- // Poisoning partial redzone.
- Value *PartialRzMagic = computePartialRzMagic(PartialSize, IRB);
- Value *PartialRzShadowAddr = ASan.memToShadow(PartialRzAligned, IRB);
- IRB.CreateStore(PartialRzMagic,
- IRB.CreateIntToPtr(PartialRzShadowAddr, Int32PtrTy));
-
- // RightRzAddress
- // = (PartialRzAddr + AllocaRzMask) & ~AllocaRzMask
- Value *RightRzAddress = IRB.CreateAnd(
- IRB.CreateAdd(PartialRzAddr, AllocaRzMask), NotAllocaRzMask);
-
- // Poisoning right redzone.
- AllocaCall.RightRzAddr = ASan.memToShadow(RightRzAddress, IRB);
- IRB.CreateStore(ConstantInt::get(IRB.getInt32Ty(), kAsanAllocaRightMagic),
- IRB.CreateIntToPtr(AllocaCall.RightRzAddr, Int32PtrTy));
+ Value *NewAddressPtr = IRB.CreateIntToPtr(NewAddress, AI->getType());
- // Replace all uses of AddessReturnedByAlloca with NewAddress.
+ // Replace all uses of AddessReturnedByAlloca with NewAddressPtr.
AI->replaceAllUsesWith(NewAddressPtr);
- // We are done. Erase old alloca and store left, partial and right redzones
- // shadow addresses for future unpoisoning.
+ // We are done. Erase old alloca from parent.
AI->eraseFromParent();
- NumInstrumentedDynamicAllocas++;
}
// isSafeAccess returns true if Addr is always inbounds with respect to its
Modified: llvm/trunk/test/Instrumentation/AddressSanitizer/instrument-dynamic-allocas.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/AddressSanitizer/instrument-dynamic-allocas.ll?rev=238402&r1=238401&r2=238402&view=diff
==============================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/instrument-dynamic-allocas.ll (original)
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/instrument-dynamic-allocas.ll Thu May 28 02:51:49 2015
@@ -2,17 +2,13 @@
; -asan-instrument-allocas=1
; RUN: opt < %s -asan -asan-module -asan-instrument-allocas=1 -S | FileCheck %s --check-prefix=CHECK-ALLOCA
-; RUN: opt < %s -asan -asan-module -asan-instrument-allocas=0 -S | FileCheck %s --check-prefix=CHECK-NOALLOCA
-; RUN: opt < %s -asan -asan-module -S | FileCheck %s --check-prefix=CHECK-NOALLOCA
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-unknown-linux-gnu"
define void @foo(i32 %len) sanitize_address {
entry:
-; CHECK-ALLOCA: store i32 -892679478
-; CHECK-ALLOCA: store i32 -875836469
-; CHECK-NOALLOCA-NOT: store i32 -892679478
-; CHECK-NOALLOCA-NOT: store i32 -875836469
+; CHECK-ALLOCA: __asan_alloca_poison
+; CHECK-ALLOCA: __asan_allocas_unpoison
%0 = alloca i32, align 4
%1 = alloca i8*
store volatile i32 %len, i32* %0, align 4
Removed: llvm/trunk/test/Instrumentation/AddressSanitizer/undecidable-dynamic-alloca-1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/AddressSanitizer/undecidable-dynamic-alloca-1.ll?rev=238401&view=auto
==============================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/undecidable-dynamic-alloca-1.ll (original)
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/undecidable-dynamic-alloca-1.ll (removed)
@@ -1,23 +0,0 @@
-; Test that undecidable dynamic allocas are skipped by ASan.
-
-; RUN: opt < %s -asan -asan-module -asan-instrument-allocas=1 -S | FileCheck %s
-target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
-target triple = "x86_64-unknown-linux-gnu"
-
-define void @g(i64 %n) sanitize_address {
-entry:
- %cmp = icmp sgt i64 %n, 100
- br i1 %cmp, label %do_alloca, label %done
-
-do_alloca:
-; CHECK-NOT: store i32 -892679478
- %0 = alloca i8, i64 %n, align 1
- call void @f(i8* %0)
- br label %done
-
-done:
- ret void
-}
-
-declare void @f(i8*)
-
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