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[clang][FMV][AArch64] Diagnose/ignore unreachable functions versions. (llvm#171496)
The commit llvm#150267 allows the user to override version priority. As a result it is now possible to define an unreachable function version if a higher priority version contains a subset of its FMV features. For example: target_clones("sve;priority=2", "sve2;priority=1") the sve2 version is unreachable, since if you don't have sve we can't have sve2 either. The patch emits a warning about such cases and ignores those versions when generating the resolver. Also removes their definitions.
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‎clang/include/clang/Basic/DiagnosticFrontendKinds.td‎

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@@ -398,6 +398,10 @@ def err_invalid_llvm_ir : Error<"invalid LLVM IR input: %0">;
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def err_os_unsupport_riscv_fmv : Error<
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"function multiversioning is currently only supported on Linux">;
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def warn_unreachable_version
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: Warning<"function version '%0' is unreachable; ignoring version">,
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InGroup<FunctionMultiVersioning>;
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def warn_hlsl_langstd_minimal :
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Warning<"support for HLSL language version %0 is incomplete, "
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"recommend using %1 instead">,

‎clang/lib/CodeGen/CodeGenFunction.cpp‎

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@@ -3144,6 +3144,10 @@ void CodeGenFunction::EmitAArch64MultiVersionResolver(
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Builder.SetInsertPoint(CurBlock);
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}
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// Skip unreachable versions.
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if (RO.Function == nullptr)
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continue;
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llvm::BasicBlock *RetBlock = createBasicBlock("resolver_return", Resolver);
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CGBuilderTy RetBuilder(*this, RetBlock);
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CreateMultiVersionResolverReturn(CGM, Resolver, RetBuilder, RO.Function,

‎clang/lib/CodeGen/CodeGenModule.cpp‎

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@@ -68,6 +68,7 @@
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/Hash.h"
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#include "llvm/Support/TimeProfiler.h"
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#include "llvm/TargetParser/AArch64TargetParser.h"
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#include "llvm/TargetParser/RISCVISAInfo.h"
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#include "llvm/TargetParser/Triple.h"
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#include "llvm/TargetParser/X86TargetParser.h"
@@ -4664,6 +4665,7 @@ void CodeGenModule::emitMultiVersionFunctions() {
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// in this TU. For other architectures it is always emitted.
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bool ShouldEmitResolver = !getTarget().getTriple().isAArch64();
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SmallVector<CodeGenFunction::FMVResolverOption, 10> Options;
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llvm::DenseMap<llvm::Function *, const FunctionDecl *> DeclMap;
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getContext().forEachMultiversionedFunctionVersion(
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FD, [&](const FunctionDecl *CurFD) {
@@ -4674,11 +4676,13 @@ void CodeGenModule::emitMultiVersionFunctions() {
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assert(getTarget().getTriple().isX86() && "Unsupported target");
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TA->getX86AddedFeatures(Feats);
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llvm::Function *Func = createFunction(CurFD);
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DeclMap.insert({Func, CurFD});
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Options.emplace_back(Func, Feats, TA->getX86Architecture());
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} else if (const auto *TVA = CurFD->getAttr<TargetVersionAttr>()) {
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if (TVA->isDefaultVersion() && IsDefined)
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ShouldEmitResolver = true;
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llvm::Function *Func = createFunction(CurFD);
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DeclMap.insert({Func, CurFD});
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char Delim = getTarget().getTriple().isAArch64() ? '+' : ',';
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TVA->getFeatures(Feats, Delim);
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Options.emplace_back(Func, Feats);
@@ -4689,6 +4693,7 @@ void CodeGenModule::emitMultiVersionFunctions() {
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if (TC->isDefaultVersion(I) && IsDefined)
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ShouldEmitResolver = true;
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llvm::Function *Func = createFunction(CurFD, I);
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DeclMap.insert({Func, CurFD});
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Feats.clear();
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if (getTarget().getTriple().isX86()) {
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TC->getX86Feature(Feats, I);
@@ -4734,6 +4739,24 @@ void CodeGenModule::emitMultiVersionFunctions() {
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const CodeGenFunction::FMVResolverOption &RHS) {
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return getFMVPriority(TI, LHS).ugt(getFMVPriority(TI, RHS));
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});
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// Diagnose unreachable function versions.
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if (getTarget().getTriple().isAArch64()) {
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for (auto I = Options.begin() + 1, E = Options.end(); I != E; ++I) {
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llvm::APInt RHS = llvm::AArch64::getCpuSupportsMask(I->Features);
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if (std::any_of(Options.begin(), I, [RHS](auto RO) {
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llvm::APInt LHS = llvm::AArch64::getCpuSupportsMask(RO.Features);
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return LHS.isSubsetOf(RHS);
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})) {
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Diags.Report(DeclMap[I->Function]->getLocation(),
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diag::warn_unreachable_version)
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<< I->Function->getName();
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assert(I->Function->user_empty() && "unexpected users");
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I->Function->eraseFromParent();
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I->Function = nullptr;
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}
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}
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}
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CodeGenFunction CGF(*this);
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CGF.EmitMultiVersionResolver(ResolverFunc, Options);
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‎clang/test/CodeGen/AArch64/fmv-unreachable-version.c‎

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@@ -0,0 +1,89 @@
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// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --function-signature --check-attributes --check-globals --include-generated-funcs
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// RUN: %clang_cc1 -triple aarch64-linux-gnu -verify -emit-llvm -o - %s | FileCheck %s
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__attribute__((target_version("sve;priority=5"))) int unreachable_versions(void) { return 5; }
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// expected-warning@+1 {{function version 'unreachable_versions._MlseMmops' is unreachable; ignoring version}}
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__attribute__((target_version("mops+lse;priority=1"))) int unreachable_versions(void) { return 1; }
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int foo() { return unreachable_versions(); }
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// expected-warning@+1 {{function version 'unreachable_versions._Msve2' is unreachable; ignoring version}}
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__attribute__((target_clones("sve2;priority=4", "aes+sve2;priority=3", "lse;priority=2", "default"))) int unreachable_versions(void) { return 0; }
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// expected-warning@-1 {{function version 'unreachable_versions._MaesMsve2' is unreachable; ignoring version}}
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//.
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// CHECK: @__aarch64_cpu_features = external dso_local global { i64 }
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// CHECK: @unreachable_versions = weak_odr ifunc i32 (), ptr @unreachable_versions.resolver
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//.
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// CHECK: Function Attrs: noinline nounwind optnone vscale_range(1,16)
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// CHECK-LABEL: define {{[^@]+}}@unreachable_versions._Msve
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// CHECK-SAME: () #[[ATTR0:[0-9]+]] {
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// CHECK-NEXT: entry:
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// CHECK-NEXT: ret i32 5
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//
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//
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// CHECK: Function Attrs: noinline nounwind optnone
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// CHECK-LABEL: define {{[^@]+}}@foo
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// CHECK-SAME: () #[[ATTR1:[0-9]+]] {
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// CHECK-NEXT: entry:
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// CHECK-NEXT: [[CALL:%.*]] = call i32 @unreachable_versions()
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// CHECK-NEXT: ret i32 [[CALL]]
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//
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//
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// CHECK: Function Attrs: noinline nounwind optnone vscale_range(1,16)
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// CHECK-LABEL: define {{[^@]+}}@unreachable_versions._Mlse
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// CHECK-SAME: () #[[ATTR2:[0-9]+]] {
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// CHECK-NEXT: entry:
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// CHECK-NEXT: ret i32 0
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//
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//
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// CHECK: Function Attrs: noinline nounwind optnone vscale_range(1,16)
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// CHECK-LABEL: define {{[^@]+}}@unreachable_versions.default
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// CHECK-SAME: () #[[ATTR3:[0-9]+]] {
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// CHECK-NEXT: entry:
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// CHECK-NEXT: ret i32 0
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//
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//
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// CHECK: Function Attrs: disable_sanitizer_instrumentation
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// CHECK-LABEL: define {{[^@]+}}@unreachable_versions.resolver
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// CHECK-SAME: () #[[ATTR4:[0-9]+]] comdat {
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// CHECK-NEXT: resolver_entry:
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// CHECK-NEXT: call void @__init_cpu_features_resolver()
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// CHECK-NEXT: [[TMP0:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
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// CHECK-NEXT: [[TMP1:%.*]] = and i64 [[TMP0]], 1073807616
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// CHECK-NEXT: [[TMP2:%.*]] = icmp eq i64 [[TMP1]], 1073807616
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// CHECK-NEXT: [[TMP3:%.*]] = and i1 true, [[TMP2]]
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// CHECK-NEXT: br i1 [[TMP3]], label [[RESOLVER_RETURN:%.*]], label [[RESOLVER_ELSE:%.*]]
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// CHECK: resolver_return:
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// CHECK-NEXT: ret ptr @unreachable_versions._Msve
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// CHECK: resolver_else:
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// CHECK-NEXT: [[TMP4:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
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// CHECK-NEXT: [[TMP5:%.*]] = and i64 [[TMP4]], 69793284352
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// CHECK-NEXT: [[TMP6:%.*]] = icmp eq i64 [[TMP5]], 69793284352
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// CHECK-NEXT: [[TMP7:%.*]] = and i1 true, [[TMP6]]
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// CHECK-NEXT: [[TMP8:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
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// CHECK-NEXT: [[TMP9:%.*]] = and i64 [[TMP8]], 69793317632
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// CHECK-NEXT: [[TMP10:%.*]] = icmp eq i64 [[TMP9]], 69793317632
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// CHECK-NEXT: [[TMP11:%.*]] = and i1 true, [[TMP10]]
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// CHECK-NEXT: [[TMP12:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
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// CHECK-NEXT: [[TMP13:%.*]] = and i64 [[TMP12]], 128
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// CHECK-NEXT: [[TMP14:%.*]] = icmp eq i64 [[TMP13]], 128
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// CHECK-NEXT: [[TMP15:%.*]] = and i1 true, [[TMP14]]
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// CHECK-NEXT: br i1 [[TMP15]], label [[RESOLVER_RETURN1:%.*]], label [[RESOLVER_ELSE2:%.*]]
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// CHECK: resolver_return1:
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// CHECK-NEXT: ret ptr @unreachable_versions._Mlse
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// CHECK: resolver_else2:
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// CHECK-NEXT: [[TMP16:%.*]] = load i64, ptr @__aarch64_cpu_features, align 8
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// CHECK-NEXT: [[TMP17:%.*]] = and i64 [[TMP16]], 576460752303423616
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// CHECK-NEXT: [[TMP18:%.*]] = icmp eq i64 [[TMP17]], 576460752303423616
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// CHECK-NEXT: [[TMP19:%.*]] = and i1 true, [[TMP18]]
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// CHECK-NEXT: ret ptr @unreachable_versions.default
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//
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//.
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// CHECK: attributes #[[ATTR0]] = { noinline nounwind optnone vscale_range(1,16) "fmv-features"="P0,P2,sve" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+fp-armv8,+fullfp16,+sve" }
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// CHECK: attributes #[[ATTR1]] = { noinline nounwind optnone "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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// CHECK: attributes #[[ATTR2]] = { noinline nounwind optnone vscale_range(1,16) "fmv-features"="P1,lse" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+lse" }
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// CHECK: attributes #[[ATTR3]] = { noinline nounwind optnone vscale_range(1,16) "fmv-features" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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// CHECK: attributes #[[ATTR4]] = { disable_sanitizer_instrumentation }
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//.
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// CHECK: [[META0:![0-9]+]] = !{i32 1, !"wchar_size", i32 4}
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// CHECK: [[META1:![0-9]+]] = !{!"{{.*}}clang version {{.*}}"}
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//.

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