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[CodeGen] Add a flag to disable emitting block signature strings (#96944)
Users who don't need the signature string to be emitted can use the flag to reduce code size. rdar://121933818
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‎clang/docs/ReleaseNotes.rst‎

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@@ -445,6 +445,11 @@ New Compiler Flags
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- ``-Wc++2c-compat`` group was added to help migrating existing codebases
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to upcoming C++26.
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- ``-fdisable-block-signature-string`` instructs clang not to emit the signature
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string for blocks. Disabling the string can potentially break existing code
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that relies on it. Users should carefully consider this possibiilty when using
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the flag.
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Deprecated Compiler Flags
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-------------------------
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‎clang/docs/UsersManual.rst‎

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@@ -913,6 +913,12 @@ Clang options that don't fit neatly into other categories.
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binary compatibility issues on older x86_64 targets, however, so use it with
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caution.
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.. option:: -fdisable-block-signature-string
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Instruct clang not to emit the signature string for blocks. Disabling the
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string can potentially break existing code that relies on it. Users should
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carefully consider this possibiilty when using the flag.
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.. _configuration-files:
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Configuration files

‎clang/include/clang/Basic/CodeGenOptions.def‎

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@@ -188,6 +188,7 @@ CODEGENOPT(NoImplicitFloat , 1, 0) ///< Set when -mno-implicit-float is enable
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CODEGENOPT(NullPointerIsValid , 1, 0) ///< Assume Null pointer deference is defined.
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CODEGENOPT(OpenCLCorrectlyRoundedDivSqrt, 1, 0) ///< -cl-fp32-correctly-rounded-divide-sqrt
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CODEGENOPT(HIPCorrectlyRoundedDivSqrt, 1, 1) ///< -fno-hip-fp32-correctly-rounded-divide-sqrt
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CODEGENOPT(DisableBlockSignatureString, 1, 0) ///< Set when -fdisable-block-signature-string is enabled.
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CODEGENOPT(HIPSaveKernelArgName, 1, 0) ///< Set when -fhip-kernel-arg-name is enabled.
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CODEGENOPT(UniqueInternalLinkageNames, 1, 0) ///< Internal Linkage symbols get unique names.
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CODEGENOPT(SplitMachineFunctions, 1, 0) ///< Split machine functions using profile information.

‎clang/include/clang/Driver/Options.td‎

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@@ -3477,6 +3477,11 @@ defm objc_avoid_heapify_local_blocks : BoolFOption<"objc-avoid-heapify-local-blo
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PosFlag<SetTrue, [], [ClangOption], "Try">,
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NegFlag<SetFalse, [], [ClangOption], "Don't try">,
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BothFlags<[], [CC1Option], " to avoid heapifying local blocks">>;
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defm disable_block_signature_string : BoolFOption<"disable-block-signature-string",
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CodeGenOpts<"DisableBlockSignatureString">, DefaultFalse,
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PosFlag<SetTrue, [], [ClangOption], "Disable">,
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NegFlag<SetFalse, [], [ClangOption], "Don't disable">,
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BothFlags<[], [CC1Option], " block signature string)">>;
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def fomit_frame_pointer : Flag<["-"], "fomit-frame-pointer">, Group<f_Group>,
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Visibility<[ClangOption, FlangOption]>,

‎clang/lib/CodeGen/CGBlocks.cpp‎

Lines changed: 21 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -121,11 +121,15 @@ static std::string getBlockDescriptorName(const CGBlockInfo &BlockInfo,
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Name += "_";
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}
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std::string TypeAtEncoding =
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CGM.getContext().getObjCEncodingForBlock(BlockInfo.getBlockExpr());
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/// Replace occurrences of '@' with '\1'. '@' is reserved on ELF platforms as
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/// a separator between symbol name and symbol version.
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std::replace(TypeAtEncoding.begin(), TypeAtEncoding.end(), '@', '\1');
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std::string TypeAtEncoding;
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if (!CGM.getCodeGenOpts().DisableBlockSignatureString) {
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TypeAtEncoding =
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CGM.getContext().getObjCEncodingForBlock(BlockInfo.getBlockExpr());
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/// Replace occurrences of '@' with '\1'. '@' is reserved on ELF platforms
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/// as a separator between symbol name and symbol version.
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std::replace(TypeAtEncoding.begin(), TypeAtEncoding.end(), '@', '\1');
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}
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Name += "e" + llvm::to_string(TypeAtEncoding.size()) + "_" + TypeAtEncoding;
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Name += "l" + CGM.getObjCRuntime().getRCBlockLayoutStr(CGM, BlockInfo);
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return Name;
@@ -201,9 +205,13 @@ static llvm::Constant *buildBlockDescriptor(CodeGenModule &CGM,
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}
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// Signature. Mandatory ObjC-style method descriptor @encode sequence.
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std::string typeAtEncoding =
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CGM.getContext().getObjCEncodingForBlock(blockInfo.getBlockExpr());
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elements.add(CGM.GetAddrOfConstantCString(typeAtEncoding).getPointer());
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if (CGM.getCodeGenOpts().DisableBlockSignatureString) {
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elements.addNullPointer(i8p);
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} else {
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std::string typeAtEncoding =
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CGM.getContext().getObjCEncodingForBlock(blockInfo.getBlockExpr());
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elements.add(CGM.GetAddrOfConstantCString(typeAtEncoding).getPointer());
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}
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// GC layout.
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if (C.getLangOpts().ObjC) {
@@ -814,7 +822,8 @@ llvm::Value *CodeGenFunction::EmitBlockLiteral(const CGBlockInfo &blockInfo) {
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descriptor = buildBlockDescriptor(CGM, blockInfo);
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// Compute the initial on-stack block flags.
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flags = BLOCK_HAS_SIGNATURE;
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if (!CGM.getCodeGenOpts().DisableBlockSignatureString)
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flags = BLOCK_HAS_SIGNATURE;
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if (blockInfo.HasCapturedVariableLayout)
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flags |= BLOCK_HAS_EXTENDED_LAYOUT;
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if (blockInfo.NeedsCopyDispose)
@@ -1300,7 +1309,9 @@ static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
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fields.add(CGM.getNSConcreteGlobalBlock());
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// __flags
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BlockFlags flags = BLOCK_IS_GLOBAL | BLOCK_HAS_SIGNATURE;
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BlockFlags flags = BLOCK_IS_GLOBAL;
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if (!CGM.getCodeGenOpts().DisableBlockSignatureString)
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flags |= BLOCK_HAS_SIGNATURE;
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if (blockInfo.UsesStret)
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flags |= BLOCK_USE_STRET;
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‎clang/lib/Driver/ToolChains/Clang.cpp‎

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@@ -5751,6 +5751,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
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Args.AddLastArg(CmdArgs, options::OPT_fexperimental_omit_vtable_rtti,
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options::OPT_fno_experimental_omit_vtable_rtti);
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Args.AddLastArg(CmdArgs, options::OPT_fdisable_block_signature_string,
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options::OPT_fno_disable_block_signature_string);
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// Handle segmented stacks.
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Args.addOptInFlag(CmdArgs, options::OPT_fsplit_stack,
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options::OPT_fno_split_stack);

‎clang/test/CodeGen/blocks.c‎

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@@ -1,7 +1,14 @@
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// RUN: %clang_cc1 -triple i386-unknown-unknown %s -emit-llvm -Wno-strict-prototypes -o - -fblocks | FileCheck %s
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// RUN: %clang_cc1 -triple i386-unknown-unknown %s -emit-llvm -Wno-strict-prototypes -o - -fblocks | FileCheck --check-prefix=CHECK --check-prefix=SIG_STR %s
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// RUN: %clang_cc1 -triple i386-unknown-unknown %s -emit-llvm -Wno-strict-prototypes -o - -fblocks -fdisable-block-signature-string | FileCheck --check-prefix=CHECK --check-prefix=NO_SIG_STR %s
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3-
// CHECK: @{{.*}} = internal constant { i32, i32, ptr, ptr, ptr, ptr } { i32 0, i32 24, ptr @__copy_helper_block_4_20r, ptr @__destroy_helper_block_4_20r, ptr @{{.*}}, ptr null }, align 4
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// CHECK: @[[BLOCK_DESCRIPTOR_TMP21:.*]] = internal constant { i32, i32, ptr, ptr, ptr, ptr } { i32 0, i32 24, ptr @__copy_helper_block_4_20r, ptr @__destroy_helper_block_4_20r, ptr @{{.*}}, ptr null }, align 4
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// SIG_STR: @[[STR:.*]] = private unnamed_addr constant [6 x i8] c"v4@?0\00", align 1
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// SIG_STR: @{{.*}} = internal constant { ptr, i32, i32, ptr, ptr } { ptr @_NSConcreteGlobalBlock, i32 1342177280, i32 0, ptr @f_block_invoke, ptr @{{.*}} }, align 4
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// NO_SIG_STR: @{{.*}} = internal constant { ptr, i32, i32, ptr, ptr } { ptr @_NSConcreteGlobalBlock, i32 268435456, i32 0, ptr @f_block_invoke, ptr @{{.*}} }, align 4
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// SIG_STR: @{{.*}} = internal constant { i32, i32, ptr, ptr, ptr, ptr } { i32 0, i32 24, ptr @__copy_helper_block_4_20r, ptr @__destroy_helper_block_4_20r, ptr @[[STR]], ptr null }, align 4
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// SIG_STR: @[[BLOCK_DESCRIPTOR_TMP21:.*]] = internal constant { i32, i32, ptr, ptr, ptr, ptr } { i32 0, i32 24, ptr @__copy_helper_block_4_20r, ptr @__destroy_helper_block_4_20r, ptr @[[STR]], ptr null }, align 4
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// NO_SIG_STR: @{{.*}} = internal constant { i32, i32, ptr, ptr, ptr, ptr } { i32 0, i32 24, ptr @__copy_helper_block_4_20r, ptr @__destroy_helper_block_4_20r, ptr null, ptr null }, align 4
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// NO_SIG_STR: @[[BLOCK_DESCRIPTOR_TMP21:.*]] = internal constant { i32, i32, ptr, ptr, ptr, ptr } { i32 0, i32 24, ptr @__copy_helper_block_4_20r, ptr @__destroy_helper_block_4_20r, ptr null, ptr null }, align 4
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void (^f)(void) = ^{};
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‎clang/test/CodeGenObjC/blocks.m‎

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@@ -1,9 +1,13 @@
1-
// RUN: %clang_cc1 -triple i386-apple-darwin9 -fobjc-runtime=macosx-fragile-10.5 -emit-llvm -fblocks -Wno-strict-prototypes -o - %s | FileCheck %s
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// RUN: %clang_cc1 -triple i386-apple-darwin9 -fobjc-runtime=macosx-fragile-10.5 -emit-llvm -fblocks -Wno-strict-prototypes -o - %s | FileCheck --check-prefix=CHECK --check-prefix=SIG_STR %s
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// RUN: %clang_cc1 -triple i386-apple-darwin9 -fobjc-runtime=macosx-fragile-10.5 -emit-llvm -fblocks -Wno-strict-prototypes -fdisable-block-signature-string -o - %s | FileCheck --check-prefix=CHECK --check-prefix=NO_SIG_STR %s
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// Check that there is only one capture (20o) in the copy/dispose function
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// names.
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// CHECK: @[[BLOCK_DESCRIPTOR0:.*]] = linkonce_odr hidden unnamed_addr constant { i32, i32, ptr, ptr, ptr, i32 } { i32 0, i32 28, ptr @__copy_helper_block_4_20o, ptr @__destroy_helper_block_4_20o, ptr @{{.*}}, i32 512 },
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// SIG_STR: @[[STR3:.*]] = private unnamed_addr constant [6 x i8] c"v4@?0\00", align 1
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// SIG_STR: @[[BLOCK_DESCRIPTOR0:"__block_descriptor_28_4_20o_e5_v4\\01\?0l"]] = linkonce_odr hidden unnamed_addr constant { i32, i32, ptr, ptr, ptr, i32 } { i32 0, i32 28, ptr @__copy_helper_block_4_20o, ptr @__destroy_helper_block_4_20o, ptr @[[STR3]], i32 512 },
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// NO_SIG_STR: @[[BLOCK_DESCRIPTOR0:__block_descriptor_28_4_20o_e0_l]] = linkonce_odr hidden unnamed_addr constant { i32, i32, ptr, ptr, ptr, i32 } { i32 0, i32 28, ptr @__copy_helper_block_4_20o, ptr @__destroy_helper_block_4_20o, ptr null, i32 512 },
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void (^gb0)(void);
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@@ -132,6 +136,9 @@ void test5(A *a) {
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}
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// CHECK-LABEL: define void @test5(
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// CHECK: %[[FLAGS:.*]] = getelementptr inbounds <{ ptr, i32, i32, ptr, ptr, ptr, ptr }>, ptr %{{.*}}, i32 0, i32 1
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// SIG_STR: store i32 -1040187392, ptr %[[FLAGS]], align 4
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// NO_SIG_STR: store i32 -2113929216, ptr %[[FLAGS]], align 4
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// CHECK: %[[V0:.*]] = getelementptr inbounds <{ ptr, i32, i32, ptr, ptr, ptr, ptr }>, ptr %{{.*}}, i32 0, i32 4
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// CHECK: store ptr @[[BLOCK_DESCRIPTOR0]], ptr %[[V0]],
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