[x86/SLH] Add a real Clang flag and LLVM IR attribute for Speculative Load Hardening.

[chandlerc]

Summary

Wires up the existing pass to work with a proper IR attribute rather
than just a hidden/internal flag. The internal flag continues to work
for now, but I'll likely remove it soon.

Most of the churn here is adding the IR attribute. I talked about this
Kristof Beyls and he seemed at least initially OK with this direction.
The idea of using a full attribute here is that we *do* expect at least
some forms of this for other architectures. There isn't anything
*inherently* x86-specific about this technique, just that we only have
an implementation for x86 at the moment.

While we could potentially expose this as a Clang-level attribute as
well, that seems like a good question to defer for the moment as it
isn't 100% clear whether that or some other programmer interface (or
both?) would be best. We'll defer the programmer interface side of this
for now, but at least get to the point where the feature can be enabled
without relying on implementation details.

This also allows us to do something that was really hard before: we can
enable *just* the indirect call retpolines when using SLH. For x86, we
don't have any other way to mitigate indirect calls. Other architectures
may take a different approach of course, and none of this is surfaced to
user-level flags.

I can split this patch up into an LLVM-side and a Clang-side, but it
seemed honestly harder to review there, as this way it is clear how
these pieces are intended to be used. That said, if reviewers would like
them split, I'm happy to oblige.

[rnk]

It makes sense to me to do this all in one go and defer the clang __attribute__ until later.

llvm/include/llvm/IR/Attributes.td

250

I can't tell if this is just vim fixing the lack of a proper trailing newline, but revert any whitespace change if possible.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

1169

These appear to repeat LLVMBitcodes.h, unless I am mistaken. Weird. Anyway, fixing that is out of scope.

[rsmith]

clang/include/clang/Driver/Options.td

2006–2009

We usually only provide -cc1 flags to switch into the non-default state.

clang/include/clang/Frontend/CodeGenOptions.def

214

Spaces rather than underscores here.

clang/lib/Driver/ToolChains/Arch/X86.cpp

169–170

-mspeculative-load-hardening -mretpoline-external-thunk does not enable +retpoline-indirect-branches (but -mretpoline-external-thunk by itself does). Is that intentional?

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

1169

The values "above the fold" in Phabricator aren't all the same as the enum value plus one. *shrug*

[chandlerc]

Address review comments.

[chandlerc]

Thanks, should all be addressed now.

clang/lib/Driver/ToolChains/Arch/X86.cpp

169–170

Yes, as that's is specifically useful (and that is one thing that motivated my above comment that we should remove the ability to use -mretpoline-external-thunk by itself eventually).

You might only need SLH's minimal retpolines, but you might need to provide your own thunks for them in the Kernel for example.

llvm/include/llvm/IR/Attributes.td

250

Soryr, my annoying editor. Will fix before submit.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

1169

Yeah, this isn't factorable easily. Anyways....

[chandlerc]

Add a test file that I somehow missed earlier (sorry about that).

[rsmith]

clang/lib/Frontend/CompilerInvocation.cpp

1150

You can just use hasArg(OPT_mspeculative_load_hardening) here.

[kristof.beyls]

llvm/docs/LangRef.rst

1659–1661

It feels wrong to me to have source code that is annotated to get hardened, but that actually will not get hardened (whether it is due to it being inlined somewhere or due to any other automatic behind-the-back-of-the-developer transformation). I fear this may lower trust in the protection this attribute provides.
I assume there is a use case where the developer wants to indicate "no hardening in this function nor in any functions inlined here". If that needs to be supported, my feel is that we may need to support that in another way.
I guess that there must be some cases where just duplicating the function to be inlined in the source code into a hardened and a non-hardened version could be too hard to do for some programs.
So, in short, I don't know what the best solution here is. I just want to raise my concern that I don't think it's a good idea that functions that are marked to be hardened end up not getting hardened under some circumstances.

[chandlerc]

Move to a more conservative model suggested by Kristof.

[chandlerc]

llvm/docs/LangRef.rst

1659–1661

I actually started out with this, so I'm very sympathetic to the perspective.

Given that you prefer it, let's start with this very conservative stance. We can always add specific mechanisms to be less conservative later, but I agree that it seems much better to start with a safe position.

[kristof.beyls]

I'm not an expert on many of the areas touched by this patch, but it looks fine from me from a high-level point-of-view, modulo a few nits I have on a few comments.

clang/lib/Driver/ToolChains/Arch/X86.cpp

151

s/deprecated/deprecating/
s/warning/warn/

llvm/include/llvm/IR/Attributes.td

181–185

After updating the LangRef.rst text, I think this comment also needs to be updated. As is, it still documents the old inlining behaviour?
I'm also not sure in how far the comment makes most sense here. This is already documented in LangRef.rst, and AFAIK, the inlining compatibility mode is not something that is defined here?

llvm/lib/Target/X86/X86SpeculativeLoadHardening.cpp

78–82

I'm not sure, but do you really still need an option to force enable SLH when you have function attributes now to enable it?
When you generate LLVM-IR using clang, you now have a clang option to enable that function attribute on all functions, so do you still have scenarios where you need an LLVM backend option to override the function attribute?

llvm/lib/Target/X86/X86TargetMachine.cpp

474

I guess this is true for some other passes too, and they don't add such a comment here. Maybe best to remove this comment if my guess is right?

[chandlerc]

All outstanding comments addressed, and landing this. Thanks all for the reviews and let me know if I missed anything.

llvm/include/llvm/IR/Attributes.td

181–185

Updated the comment.

You can override the compatibility here -- see the CompatRule productions just before the MergeRule ones.

I'd like this to be documented near the code in addition to in the langref personally. It reminds the reader to look below at the rule sections.

llvm/lib/Target/X86/X86SpeculativeLoadHardening.cpp

78–82

Long term, no, we don't.

I just have some users that are already passing this flag. Out of convenience, I wanted to leave this working until they have picked up the new version of Clang and LLVM and migrated. I don't expect it to last long (a week or two?).

clang/include/clang/Driver/Options.td

 def mno_red_zone : Flag<["-"], "mno-red-zone">, Group<m_Group>;
 def mno_relax_all : Flag<["-"], "mno-relax-all">, Group<m_Group>;
 def mno_rtd: Flag<["-"], "mno-rtd">, Group<m_Group>;
 def mno_soft_float : Flag<["-"], "mno-soft-float">, Group<m_Group>;
 def mno_stackrealign : Flag<["-"], "mno-stackrealign">, Group<m_Group>;
 
 def mretpoline : Flag<["-"], "mretpoline">, Group<m_Group>, Flags<[CoreOption,DriverOption]>;
 def mno_retpoline : Flag<["-"], "mno-retpoline">, Group<m_Group>, Flags<[CoreOption,DriverOption]>;
+def mspeculative_load_hardening : Flag<["-"], "mspeculative-load-hardening">,
+  Group<m_Group>, Flags<[CoreOption,CC1Option]>;
+def mno_speculative_load_hardening : Flag<["-"], "mno-speculative-load-hardening">,
+  Group<m_Group>, Flags<[CoreOption]>;
 
 def mrelax : Flag<["-"], "mrelax">, Group<m_riscv_Features_Group>,
   HelpText<"Enable linker relaxation">;
 def mno_relax : Flag<["-"], "mno-relax">, Group<m_riscv_Features_Group>,
   HelpText<"Disable linker relaxation">;
 
 def munaligned_access : Flag<["-"], "munaligned-access">, Group<m_arm_Features_Group>,
   HelpText<"Allow memory accesses to be unaligned (AArch32/AArch64 only)">;

clang/include/clang/Frontend/CodeGenOptions.def

CODEGENOPT(SanitizeCoverageTracePCGuard, 1, 0) ///< Enable PC tracing with guard
                                                ///< in sanitizer coverage.
 CODEGENOPT(SanitizeCoverageInline8bitCounters, 1, 0) ///< Use inline 8bit counters.
 CODEGENOPT(SanitizeCoveragePCTable, 1, 0) ///< Create a PC Table.
 CODEGENOPT(SanitizeCoverageNoPrune, 1, 0) ///< Disable coverage pruning.
 CODEGENOPT(SanitizeCoverageStackDepth, 1, 0) ///< Enable max stack depth tracing
 CODEGENOPT(SanitizeStats     , 1, 0) ///< Collect statistics for sanitizers.
 CODEGENOPT(SimplifyLibCalls  , 1, 1) ///< Set when -fbuiltin is enabled.
 CODEGENOPT(SoftFloat         , 1, 0) ///< -soft-float.
+CODEGENOPT(SpeculativeLoadHardening, 1, 0) ///< Enable speculative load hardening.
 CODEGENOPT(FineGrainedBitfieldAccesses, 1, 0) ///< Enable fine-grained bitfield accesses.
 CODEGENOPT(StrictEnums       , 1, 0) ///< Optimize based on strict enum definition.
 CODEGENOPT(StrictVTablePointers, 1, 0) ///< Optimize based on the strict vtable pointers
 CODEGENOPT(TimePasses        , 1, 0) ///< Set when -ftime-report is enabled.
 CODEGENOPT(UnrollLoops       , 1, 0) ///< Control whether loops are unrolled.
 CODEGENOPT(RerollLoops       , 1, 0) ///< Control whether loops are rerolled.
 CODEGENOPT(NoUseJumpTables   , 1, 0) ///< Set when -fno-jump-tables is enabled.
 CODEGENOPT(UnsafeFPMath      , 1, 0) ///< Allow unsafe floating point optzns.

clang/lib/CodeGen/CGCall.cpp

if (!CodeGenOpts.PreferVectorWidth.empty() &&
         CodeGenOpts.PreferVectorWidth != "none")
       FuncAttrs.addAttribute("prefer-vector-width",
                              CodeGenOpts.PreferVectorWidth);
 
     if (CodeGenOpts.StackRealignment)
       FuncAttrs.addAttribute("stackrealign");
     if (CodeGenOpts.Backchain)
       FuncAttrs.addAttribute("backchain");
+
+    if (CodeGenOpts.SpeculativeLoadHardening)
+      FuncAttrs.addAttribute(llvm::Attribute::SpeculativeLoadHardening);
   }
 
   if (getLangOpts().assumeFunctionsAreConvergent()) {
     // Conservatively, mark all functions and calls in CUDA and OpenCL as
     // convergent (meaning, they may call an intrinsically convergent op, such
     // as __syncthreads() / barrier(), and so can't have certain optimizations
     // applied around them).  LLVM will remove this attribute where it safely
     // can.

clang/lib/Driver/ToolChains/Arch/X86.cpp

if (ArchType == llvm::Triple::x86_64) {
       Features.push_back("+sse4.2");
       Features.push_back("+popcnt");
     } else
       Features.push_back("+ssse3");
   }
 
   // Translate the high level `-mretpoline` flag to the specific target feature
   // flags. We also detect if the user asked for retpoline external thunks but
-  // failed to ask for retpolines themselves. This is a bit hacky but keeps
-  // existing usages working. We should consider deprecated this and instead
-  // warning if the user requests external retpoline thunks and *doesn't*
-  // request some form of retpolines.
-  if (Args.hasArgNoClaim(options::OPT_mretpoline, options::OPT_mno_retpoline)) {
+  // failed to ask for retpolines themselves (through any of the different
+  // flags). This is a bit hacky but keeps existing usages working. We should
+  // consider deprecated this and instead warning if the user requests external
+  // retpoline thunks and *doesn't* request some form of retpolines.
+  if (Args.hasArgNoClaim(options::OPT_mretpoline, options::OPT_mno_retpoline,
+                         options::OPT_mspeculative_load_hardening,
+                         options::OPT_mno_speculative_load_hardening)) {
     if (Args.hasFlag(options::OPT_mretpoline, options::OPT_mno_retpoline,
                      false)) {
       Features.push_back("+retpoline-indirect-calls");
       Features.push_back("+retpoline-indirect-branches");
+    } else if (Args.hasFlag(options::OPT_mspeculative_load_hardening,
+                            options::OPT_mno_speculative_load_hardening,
+                            false)) {
+      // On x86, speculative load hardening relies on at least using retpolines
+      // for indirect calls.
+      Features.push_back("+retpoline-indirect-calls");
     }
   } else if (Args.hasFlag(options::OPT_mretpoline_external_thunk,
                           options::OPT_mno_retpoline_external_thunk, false)) {
     // FIXME: Add a warning about failing to specify `-mretpoline` and
     // eventually switch to an error here.
     Features.push_back("+retpoline-indirect-calls");
     Features.push_back("+retpoline-indirect-branches");
   }
 
   // Now add any that the user explicitly requested on the command line,
   // which may override the defaults.
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_x86_Features_Group);
 }

clang/lib/Driver/ToolChains/Clang.cpp

if (A->getOption().matches(options::OPT_freroll_loops))
       CmdArgs.push_back("-freroll-loops");
 
   Args.AddLastArg(CmdArgs, options::OPT_fwritable_strings);
   Args.AddLastArg(CmdArgs, options::OPT_funroll_loops,
                   options::OPT_fno_unroll_loops);
 
   Args.AddLastArg(CmdArgs, options::OPT_pthread);
 
+  Args.AddLastArg(CmdArgs, options::OPT_mspeculative_load_hardening,
+                  options::OPT_mno_speculative_load_hardening);
+
   RenderSSPOptions(getToolChain(), Args, CmdArgs, KernelOrKext);
 
   // Translate -mstackrealign
   if (Args.hasFlag(options::OPT_mstackrealign, options::OPT_mno_stackrealign,
                    false))
     CmdArgs.push_back(Args.MakeArgString("-mstackrealign"));
 
   if (Args.hasArg(options::OPT_mstack_alignment)) {

clang/lib/Frontend/CompilerInvocation.cpp

else if (SignScope.equals_lower("non-leaf"))
           CodeGenOptions::SignReturnAddressScope::NonLeaf);
     else
       Diags.Report(diag::err_drv_invalid_value)
           << A->getAsString(Args) << A->getValue();
   }
 
   Opts.KeepStaticConsts = Args.hasArg(OPT_fkeep_static_consts);
 
+  Opts.SpeculativeLoadHardening =
+      Args.hasFlag(OPT_mspeculative_load_hardening,
+                   OPT_mno_speculative_load_hardening, false);
+
   return Success;
 }
 
 static void ParseDependencyOutputArgs(DependencyOutputOptions &Opts,
                                       ArgList &Args) {
   Opts.OutputFile = Args.getLastArgValue(OPT_dependency_file);
   Opts.Targets = Args.getAllArgValues(OPT_MT);
   Opts.IncludeSystemHeaders = Args.hasArg(OPT_sys_header_deps);

clang/test/CodeGen/attr-speculative-load-hardening.c

+// RUN: %clang_cc1 -mspeculative-load-hardening -disable-llvm-passes -emit-llvm %s -o - | FileCheck %s -check-prefix=SLH
+//
+// Check that we set the attribute on each function.
+
+int test1() {
+  return 42;
+}
+// SLH: @{{.*}}test1{{.*}}[[SLH:#[0-9]+]]
+
+// SLH: attributes [[SLH]] = { {{.*}}speculative_load_hardening{{.*}} }
+

clang/test/Driver/x86-target-features.c

 // RETPOLINE: "-target-feature" "+retpoline-indirect-calls" "-target-feature" "+retpoline-indirect-branches"
 // NO-RETPOLINE-NOT: retpoline
 
 // RUN: %clang -target i386-linux-gnu -mretpoline -mretpoline-external-thunk %s -### -o %t.o 2>&1 | FileCheck -check-prefix=RETPOLINE-EXTERNAL-THUNK %s
 // RUN: %clang -target i386-linux-gnu -mretpoline -mno-retpoline-external-thunk %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-RETPOLINE-EXTERNAL-THUNK %s
 // RETPOLINE-EXTERNAL-THUNK: "-target-feature" "+retpoline-external-thunk"
 // NO-RETPOLINE-EXTERNAL-THUNK: "-target-feature" "-retpoline-external-thunk"
 
+// RUN: %clang -target i386-linux-gnu -mspeculative-load-hardening %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLH %s
+// RUN: %clang -target i386-linux-gnu -mretpoline -mspeculative-load-hardening %s -### -o %t.o 2>&1 | FileCheck -check-prefix=RETPOLINE %s
+// RUN: %clang -target i386-linux-gnu -mno-speculative-load-hardening %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-SLH %s
+// SLH-NOT: retpoline
+// SLH: "-target-feature" "+retpoline-indirect-calls"
+// SLH-NOT: retpoline
+// SLH: "-mspeculative-load-hardening"
+// NO-SLH-NOT: retpoline
+
 // RUN: %clang -target i386-linux-gnu -mwaitpkg %s -### -o %t.o 2>&1 | FileCheck -check-prefix=WAITPKG %s
 // RUN: %clang -target i386-linux-gnu -mno-waitpkg %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-WAITPKG %s
 // WAITPKG: "-target-feature" "+waitpkg"
 // NO-WAITPKG: "-target-feature" "-waitpkg"
 
 // RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mmovdiri %s -### -o %t.o 2>&1 | FileCheck -check-prefix=MOVDIRI %s
 // RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mno-movdiri %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-MOVDIRI %s
 // MOVDIRI: "-target-feature" "+movdiri"

llvm/docs/LangRef.rst

``sanitize_memory``
     of accesses to uninitialized memory) are enabled for this function.
 ``sanitize_thread``
     This attribute indicates that ThreadSanitizer checks
     (dynamic thread safety analysis) are enabled for this function.
 ``sanitize_hwaddress``
     This attribute indicates that HWAddressSanitizer checks
     (dynamic address safety analysis based on tagged pointers) are enabled for
     this function.
+``speculative_load_hardening``
+    This attribute indicates that
+    `Speculative Load Hardening <https://llvm.org/docs/SpeculativeLoadHardening.html>`_
+    should be enabled for the function body. This is a best-effort attempt to
+    mitigate all known speculative execution information leak vulnerabilities
+    that are based on the fundamental principles of modern processors'
+    speculative execution. These vulnerabilities are classified as "Spectre
+    variant #1" vulnerabilities typically. Notably, this does not attempt to
+    mitigate any vulnerabilities where the speculative execution and/or
+    prediction devices of specific processors can be *completely* undermined
+    (such as "Branch Target Injection", a.k.a, "Spectre variant #2"). Instead,
+    this is a target-independent request to harden against the completely
+    generic risk posed by speculative execution to incorrectly load secret data,
+    making it available to some micro-architectural side-channel for information
+    leak. For a processor without any speculative execution or predictors, this
+    is expected to be a no-op.
+
+    When inlining, the attribute is sticky. Inlining a function that carries
+    this attribute will cause the caller to gain the attribute. This is intended
+    to provide a maximally conservative model where the code in a function
+    annotated with this attribute will always (even after inlining) end up
+    hardened.
 ``speculatable``
     This function attribute indicates that the function does not have any
     effects besides calculating its result and does not have undefined behavior.
     Note that ``speculatable`` is not enough to conclude that along any
     particular execution path the number of calls to this function will not be
     externally observable. This attribute is only valid on functions
     and declarations, not on individual call sites. If a function is
     incorrectly marked as speculatable and really does exhibit
     undefined behavior, the undefined behavior may be observed even

llvm/include/llvm/Bitcode/LLVMBitCodes.h

enum AttributeKindCodes {
   ATTR_KIND_ALLOC_SIZE = 51,
   ATTR_KIND_WRITEONLY = 52,
   ATTR_KIND_SPECULATABLE = 53,
   ATTR_KIND_STRICT_FP = 54,
   ATTR_KIND_SANITIZE_HWADDRESS = 55,
   ATTR_KIND_NOCF_CHECK = 56,
   ATTR_KIND_OPT_FOR_FUZZING = 57,
   ATTR_KIND_SHADOWCALLSTACK = 58,
+  ATTR_KIND_SPECULATIVE_LOAD_HARDENING = 59,
 };
 
 enum ComdatSelectionKindCodes {
   COMDAT_SELECTION_KIND_ANY = 1,
   COMDAT_SELECTION_KIND_EXACT_MATCH = 2,
   COMDAT_SELECTION_KIND_LARGEST = 3,
   COMDAT_SELECTION_KIND_NO_DUPLICATES = 4,
   COMDAT_SELECTION_KIND_SAME_SIZE = 5,

llvm/include/llvm/IR/Attributes.td

 def SanitizeThread : EnumAttr<"sanitize_thread">;
 
 /// MemorySanitizer is on.
 def SanitizeMemory : EnumAttr<"sanitize_memory">;
 
 /// HWAddressSanitizer is on.
 def SanitizeHWAddress : EnumAttr<"sanitize_hwaddress">;
 
+/// Speculative Load Hardening is enabled.
+///
+/// Note that this uses the default compatibility (always compatible during
+/// inlining) and the default merge strategy of retaining the caller's
+/// attribute. This specifically matches the intent for this attribute which is
+/// that the context dominates, and inlined code will become hardened or lose
+/// its hardening based on the caller's attribute.
+def SpeculativeLoadHardening : EnumAttr<"speculative_load_hardening">;
+
 /// Argument is swift error.
 def SwiftError : EnumAttr<"swifterror">;
 
 /// Argument is swift self/context.
 def SwiftSelf : EnumAttr<"swiftself">;
 
 /// Function must be in a unwind table.
 def UWTable : EnumAttr<"uwtable">;

 
 def : MergeRule<"setAND<LessPreciseFPMADAttr>">;
 def : MergeRule<"setAND<NoInfsFPMathAttr>">;
 def : MergeRule<"setAND<NoNansFPMathAttr>">;
 def : MergeRule<"setAND<UnsafeFPMathAttr>">;
 def : MergeRule<"setOR<NoImplicitFloatAttr>">;
 def : MergeRule<"setOR<NoJumpTablesAttr>">;
 def : MergeRule<"setOR<ProfileSampleAccurateAttr>">;
+def : MergeRule<"setOR<SpeculativeLoadHardeningAttr>">;
 def : MergeRule<"adjustCallerSSPLevel">;
 def : MergeRule<"adjustCallerStackProbes">;
 def : MergeRule<"adjustCallerStackProbeSize">;
 def : MergeRule<"adjustMinLegalVectorWidth">;
 def : MergeRule<"adjustNullPointerValidAttr">;

llvm/lib/AsmParser/LLLexer.cpp

#define KEYWORD(STR)                                                           \
   KEYWORD(sspstrong);
   KEYWORD(strictfp);
   KEYWORD(safestack);
   KEYWORD(shadowcallstack);
   KEYWORD(sanitize_address);
   KEYWORD(sanitize_hwaddress);
   KEYWORD(sanitize_thread);
   KEYWORD(sanitize_memory);
+  KEYWORD(speculative_load_hardening);
   KEYWORD(swifterror);
   KEYWORD(swiftself);
   KEYWORD(uwtable);
   KEYWORD(writeonly);
   KEYWORD(zeroext);
 
   KEYWORD(type);
   KEYWORD(opaque);

llvm/lib/AsmParser/LLParser.cpp

while (true) {
     case lltok::kw_sanitize_address:
       B.addAttribute(Attribute::SanitizeAddress); break;
     case lltok::kw_sanitize_hwaddress:
       B.addAttribute(Attribute::SanitizeHWAddress); break;
     case lltok::kw_sanitize_thread:
       B.addAttribute(Attribute::SanitizeThread); break;
     case lltok::kw_sanitize_memory:
       B.addAttribute(Attribute::SanitizeMemory); break;
+    case lltok::kw_speculative_load_hardening:
+      B.addAttribute(Attribute::SpeculativeLoadHardening);
+      break;
     case lltok::kw_strictfp: B.addAttribute(Attribute::StrictFP); break;
     case lltok::kw_uwtable: B.addAttribute(Attribute::UWTable); break;
     case lltok::kw_writeonly: B.addAttribute(Attribute::WriteOnly); break;
 
     // Error handling.
     case lltok::kw_inreg:
     case lltok::kw_signext:
     case lltok::kw_zeroext:
while (true) {
     case lltok::kw_optforfuzzing:
     case lltok::kw_optnone:
     case lltok::kw_optsize:
     case lltok::kw_returns_twice:
     case lltok::kw_sanitize_address:
     case lltok::kw_sanitize_hwaddress:
     case lltok::kw_sanitize_memory:
     case lltok::kw_sanitize_thread:
+    case lltok::kw_speculative_load_hardening:
     case lltok::kw_ssp:
     case lltok::kw_sspreq:
     case lltok::kw_sspstrong:
     case lltok::kw_safestack:
     case lltok::kw_shadowcallstack:
     case lltok::kw_strictfp:
     case lltok::kw_uwtable:
       HaveError |= Error(Lex.getLoc(), "invalid use of function-only attribute");
while (true) {
     case lltok::kw_optforfuzzing:
     case lltok::kw_optnone:
     case lltok::kw_optsize:
     case lltok::kw_returns_twice:
     case lltok::kw_sanitize_address:
     case lltok::kw_sanitize_hwaddress:
     case lltok::kw_sanitize_memory:
     case lltok::kw_sanitize_thread:
+    case lltok::kw_speculative_load_hardening:
     case lltok::kw_ssp:
     case lltok::kw_sspreq:
     case lltok::kw_sspstrong:
     case lltok::kw_safestack:
     case lltok::kw_shadowcallstack:
     case lltok::kw_strictfp:
     case lltok::kw_uwtable:
       HaveError |= Error(Lex.getLoc(), "invalid use of function-only attribute");

llvm/lib/AsmParser/LLToken.h

enum Kind {
   kw_ssp,
   kw_sspreq,
   kw_sspstrong,
   kw_safestack,
   kw_shadowcallstack,
   kw_sret,
   kw_sanitize_thread,
   kw_sanitize_memory,
+  kw_speculative_load_hardening,
   kw_strictfp,
   kw_swifterror,
   kw_swiftself,
   kw_uwtable,
   kw_writeonly,
   kw_zeroext,
 
   kw_type,

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

static uint64_t getRawAttributeMask(Attribute::AttrKind Val) {
   case Attribute::SwiftError:      return 1ULL << 52;
   case Attribute::WriteOnly:       return 1ULL << 53;
   case Attribute::Speculatable:    return 1ULL << 54;
   case Attribute::StrictFP:        return 1ULL << 55;
   case Attribute::SanitizeHWAddress: return 1ULL << 56;
   case Attribute::NoCfCheck:       return 1ULL << 57;
   case Attribute::OptForFuzzing:   return 1ULL << 58;
   case Attribute::ShadowCallStack: return 1ULL << 59;
+  case Attribute::SpeculativeLoadHardening:
+    return 1ULL << 60;
   case Attribute::Dereferenceable:
     llvm_unreachable("dereferenceable attribute not supported in raw format");
     break;
   case Attribute::DereferenceableOrNull:
     llvm_unreachable("dereferenceable_or_null attribute not supported in raw "
                      "format");
     break;
   case Attribute::ArgMemOnly:
static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
   case bitc::ATTR_KIND_SANITIZE_ADDRESS:
     return Attribute::SanitizeAddress;
   case bitc::ATTR_KIND_SANITIZE_HWADDRESS:
     return Attribute::SanitizeHWAddress;
   case bitc::ATTR_KIND_SANITIZE_THREAD:
     return Attribute::SanitizeThread;
   case bitc::ATTR_KIND_SANITIZE_MEMORY:
     return Attribute::SanitizeMemory;
+  case bitc::ATTR_KIND_SPECULATIVE_LOAD_HARDENING:
+    return Attribute::SpeculativeLoadHardening;
   case bitc::ATTR_KIND_SWIFT_ERROR:
     return Attribute::SwiftError;
   case bitc::ATTR_KIND_SWIFT_SELF:
     return Attribute::SwiftSelf;
   case bitc::ATTR_KIND_UW_TABLE:
     return Attribute::UWTable;
   case bitc::ATTR_KIND_WRITEONLY:
     return Attribute::WriteOnly;

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
   case Attribute::SanitizeAddress:
     return bitc::ATTR_KIND_SANITIZE_ADDRESS;
   case Attribute::SanitizeHWAddress:
     return bitc::ATTR_KIND_SANITIZE_HWADDRESS;
   case Attribute::SanitizeThread:
     return bitc::ATTR_KIND_SANITIZE_THREAD;
   case Attribute::SanitizeMemory:
     return bitc::ATTR_KIND_SANITIZE_MEMORY;
+  case Attribute::SpeculativeLoadHardening:
+    return bitc::ATTR_KIND_SPECULATIVE_LOAD_HARDENING;
   case Attribute::SwiftError:
     return bitc::ATTR_KIND_SWIFT_ERROR;
   case Attribute::SwiftSelf:
     return bitc::ATTR_KIND_SWIFT_SELF;
   case Attribute::UWTable:
     return bitc::ATTR_KIND_UW_TABLE;
   case Attribute::WriteOnly:
     return bitc::ATTR_KIND_WRITEONLY;

llvm/lib/IR/Attributes.cpp

std::string Attribute::getAsString(bool InAttrGrp) const {
   if (hasAttribute(Attribute::WriteOnly))
     return "writeonly";
   if (hasAttribute(Attribute::Returned))
     return "returned";
   if (hasAttribute(Attribute::ReturnsTwice))
     return "returns_twice";
   if (hasAttribute(Attribute::SExt))
     return "signext";
+  if (hasAttribute(Attribute::SpeculativeLoadHardening))
+    return "speculative_load_hardening";
   if (hasAttribute(Attribute::Speculatable))
     return "speculatable";
   if (hasAttribute(Attribute::StackProtect))
     return "ssp";
   if (hasAttribute(Attribute::StackProtectReq))
     return "sspreq";
   if (hasAttribute(Attribute::StackProtectStrong))
     return "sspstrong";

llvm/lib/IR/Verifier.cpp

static bool isFuncOnlyAttr(Attribute::AttrKind Kind) {
   case Attribute::OptimizeNone:
   case Attribute::JumpTable:
   case Attribute::Convergent:
   case Attribute::ArgMemOnly:
   case Attribute::NoRecurse:
   case Attribute::InaccessibleMemOnly:
   case Attribute::InaccessibleMemOrArgMemOnly:
   case Attribute::AllocSize:
+  case Attribute::SpeculativeLoadHardening:
   case Attribute::Speculatable:
   case Attribute::StrictFP:
     return true;
   default:
     break;
   }
   return false;
 }

llvm/lib/Target/X86/X86SpeculativeLoadHardening.cpp

STATISTIC(NumAddrRegsHardened,
           "Number of address mode used registers hardaned");
 STATISTIC(NumPostLoadRegsHardened,
           "Number of post-load register values hardened");
 STATISTIC(NumCallsOrJumpsHardened,
           "Number of calls or jumps requiring extra hardening");
 STATISTIC(NumInstsInserted, "Number of instructions inserted");
 STATISTIC(NumLFENCEsInserted, "Number of lfence instructions inserted");
 
+static cl::opt<bool> EnableSpeculativeLoadHardening(
+    "x86-speculative-load-hardening",
+    cl::desc("Force enable speculative load hardening"), cl::init(false),
+    cl::Hidden);
+
 static cl::opt<bool> HardenEdgesWithLFENCE(
     PASS_KEY "-lfence",
     cl::desc(
         "Use LFENCE along each conditional edge to harden against speculative "
         "loads rather than conditional movs and poisoned pointers."),
     cl::init(false), cl::Hidden);
 
 static cl::opt<bool> EnablePostLoadHardening(
static bool hasVulnerableLoad(MachineFunction &MF) {
   return false;
 }
 
 bool X86SpeculativeLoadHardeningPass::runOnMachineFunction(
     MachineFunction &MF) {
   LLVM_DEBUG(dbgs() << "********** " << getPassName() << " : " << MF.getName()
                     << " **********\n");
 
+  // Only run if this pass is forced enabled or we detect the relevant function
+  // attribute requesting SLH.
+  if (!EnableSpeculativeLoadHardening &&
+      !MF.getFunction().hasFnAttribute(Attribute::SpeculativeLoadHardening))
+    return false;
+
   Subtarget = &MF.getSubtarget<X86Subtarget>();
   MRI = &MF.getRegInfo();
   TII = Subtarget->getInstrInfo();
   TRI = Subtarget->getRegisterInfo();
 
   // FIXME: Support for 32-bit.
   PS.emplace(MF, &X86::GR64_NOSPRegClass);
 

llvm/lib/Target/X86/X86TargetMachine.cpp

 #include <string>
 
 using namespace llvm;
 
 static cl::opt<bool> EnableMachineCombinerPass("x86-machine-combiner",
                                cl::desc("Enable the machine combiner pass"),
                                cl::init(true), cl::Hidden);
 
-static cl::opt<bool> EnableSpeculativeLoadHardening(
-    "x86-speculative-load-hardening",
-    cl::desc("Enable speculative load hardening"), cl::init(false), cl::Hidden);
-
 namespace llvm {
 
 void initializeWinEHStatePassPass(PassRegistry &);
 void initializeFixupLEAPassPass(PassRegistry &);
 void initializeShadowCallStackPass(PassRegistry &);
 void initializeX86CallFrameOptimizationPass(PassRegistry &);
 void initializeX86CmovConverterPassPass(PassRegistry &);
 void initializeX86ExecutionDomainFixPass(PassRegistry &);
void X86PassConfig::addPreRegAlloc() {
   if (getOptLevel() != CodeGenOpt::None) {
     addPass(&LiveRangeShrinkID);
     addPass(createX86FixupSetCC());
     addPass(createX86OptimizeLEAs());
     addPass(createX86CallFrameOptimization());
     addPass(createX86AvoidStoreForwardingBlocks());
   }
 
-  if (EnableSpeculativeLoadHardening)
-    addPass(createX86SpeculativeLoadHardeningPass());
+  // Will only run if force enabled or detects the relevant attribute.
 
   addPass(createX86FlagsCopyLoweringPass());
   addPass(createX86WinAllocaExpander());
 }
 void X86PassConfig::addMachineSSAOptimization() {
   addPass(createX86DomainReassignmentPass());
   TargetPassConfig::addMachineSSAOptimization();
 }

llvm/lib/Transforms/IPO/ForceFunctionAttrs.cpp

return StringSwitch<Attribute::AttrKind>(Kind)
       .Case("argmemonly", Attribute::ArgMemOnly)
       .Case("returns_twice", Attribute::ReturnsTwice)
       .Case("safestack", Attribute::SafeStack)
       .Case("shadowcallstack", Attribute::ShadowCallStack)
       .Case("sanitize_address", Attribute::SanitizeAddress)
       .Case("sanitize_hwaddress", Attribute::SanitizeHWAddress)
       .Case("sanitize_memory", Attribute::SanitizeMemory)
       .Case("sanitize_thread", Attribute::SanitizeThread)
+      .Case("speculative_load_hardening", Attribute::SpeculativeLoadHardening)
       .Case("ssp", Attribute::StackProtect)
       .Case("sspreq", Attribute::StackProtectReq)
       .Case("sspstrong", Attribute::StackProtectStrong)
       .Case("strictfp", Attribute::StrictFP)
       .Case("uwtable", Attribute::UWTable)
       .Default(Attribute::None);
 }
 

llvm/lib/Transforms/Utils/CodeExtractor.cpp

if (Attr.isStringAttribute()) {
       case Attribute::OptimizeNone:
       case Attribute::OptimizeForSize:
       case Attribute::SafeStack:
       case Attribute::ShadowCallStack:
       case Attribute::SanitizeAddress:
       case Attribute::SanitizeMemory:
       case Attribute::SanitizeThread:
       case Attribute::SanitizeHWAddress:
+      case Attribute::SpeculativeLoadHardening:
       case Attribute::StackProtect:
       case Attribute::StackProtectReq:
       case Attribute::StackProtectStrong:
       case Attribute::StrictFP:
       case Attribute::UWTable:
       case Attribute::NoCfCheck:
         break;
       }

llvm/test/CodeGen/X86/O0-pipeline.ll

 ; CHECK-NEXT:       Exception handling preparation
 ; CHECK-NEXT:       Safe Stack instrumentation pass
 ; CHECK-NEXT:       Insert stack protectors
 ; CHECK-NEXT:       Module Verifier
 ; CHECK-NEXT:       X86 DAG->DAG Instruction Selection
 ; CHECK-NEXT:       X86 PIC Global Base Reg Initialization
 ; CHECK-NEXT:       Expand ISel Pseudo-instructions
 ; CHECK-NEXT:       Local Stack Slot Allocation
+; CHECK-NEXT:       X86 speculative load hardening
 ; CHECK-NEXT:       MachineDominator Tree Construction
 ; CHECK-NEXT:       X86 EFLAGS copy lowering
 ; CHECK-NEXT:       X86 WinAlloca Expander
 ; CHECK-NEXT:       Eliminate PHI nodes for register allocation
 ; CHECK-NEXT:       Two-Address instruction pass
 ; CHECK-NEXT:       Fast Register Allocator
 ; CHECK-NEXT:       Bundle Machine CFG Edges
 ; CHECK-NEXT:       X86 FP Stackifier

llvm/test/CodeGen/X86/O3-pipeline.ll

 ; CHECK-NEXT:       Machine code sinking
 ; CHECK-NEXT:       Peephole Optimizations
 ; CHECK-NEXT:       Remove dead machine instructions
 ; CHECK-NEXT:       Live Range Shrink
 ; CHECK-NEXT:       X86 Fixup SetCC
 ; CHECK-NEXT:       X86 LEA Optimize
 ; CHECK-NEXT:       X86 Optimize Call Frame
 ; CHECK-NEXT:       X86 Avoid Store Forwarding Block
+; CHECK-NEXT:       X86 speculative load hardening
 ; CHECK-NEXT:       MachineDominator Tree Construction
 ; CHECK-NEXT:       X86 EFLAGS copy lowering
 ; CHECK-NEXT:       X86 WinAlloca Expander
 ; CHECK-NEXT:       Detect Dead Lanes
 ; CHECK-NEXT:       Process Implicit Definitions
 ; CHECK-NEXT:       Remove unreachable machine basic blocks
 ; CHECK-NEXT:       Live Variable Analysis
 ; CHECK-NEXT:       MachineDominator Tree Construction

llvm/test/CodeGen/X86/speculative-load-hardening-gather.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -x86-speculative-load-hardening | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s
 
 declare <4 x float> @llvm.x86.avx2.gather.d.ps(<4 x float>, i8*, <4 x i32>, <4 x float>, i8)
 
 define <4 x float> @test_llvm_x86_avx2_gather_d_ps(i8* %b, <4 x i32> %iv, <4 x float> %mask) #0 {
 ; CHECK-LABEL: test_llvm_x86_avx2_gather_d_ps:
 ; CHECK:       # %bb.0: # %entry
 ; CHECK-NEXT:    movq %rsp, %rax
 ; CHECK-NEXT:    movq $-1, %rcx

 ; CHECK-NEXT:    vmovdqa %ymm1, %ymm0
 ; CHECK-NEXT:    orq %rax, %rsp
 ; CHECK-NEXT:    retq
 entry:
   %v = call <4 x i64> @llvm.x86.avx512.gather3div4.di(<4 x i64> zeroinitializer, i8* %b, <4 x i64> %iv, i8 -1, i32 1)
   ret <4 x i64> %v
 }
 
-attributes #0 = { nounwind "target-features"="+avx2" }
-attributes #1 = { nounwind "target-features"="+avx512f" }
-attributes #2 = { nounwind "target-features"="+avx512vl" }
+attributes #0 = { nounwind speculative_load_hardening "target-features"="+avx2" }
+attributes #1 = { nounwind speculative_load_hardening "target-features"="+avx512f" }
+attributes #2 = { nounwind speculative_load_hardening "target-features"="+avx512vl" }

llvm/test/CodeGen/X86/speculative-load-hardening-indirect.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -x86-speculative-load-hardening -data-sections | FileCheck %s --check-prefix=X64
-; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -x86-speculative-load-hardening -data-sections -mattr=+retpoline | FileCheck %s --check-prefix=X64-RETPOLINE
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -data-sections | FileCheck %s --check-prefix=X64
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -data-sections -mattr=+retpoline | FileCheck %s --check-prefix=X64-RETPOLINE
 ;
 ; FIXME: Add support for 32-bit.
 
 @global_fnptr = external global i32 ()*
 
 @global_blockaddrs = constant [4 x i8*] [
   i8* blockaddress(@test_indirectbr_global, %bb0),
   i8* blockaddress(@test_indirectbr_global, %bb1),
   i8* blockaddress(@test_indirectbr_global, %bb2),
   i8* blockaddress(@test_indirectbr_global, %bb3)
 ]
 
-define i32 @test_indirect_call(i32 ()** %ptr) nounwind {
+define i32 @test_indirect_call(i32 ()** %ptr) nounwind speculative_load_hardening {
 ; X64-LABEL: test_indirect_call:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %rax
 ; X64-NEXT:    movq %rsp, %rax
 ; X64-NEXT:    movq $-1, %rcx
 ; X64-NEXT:    sarq $63, %rax
 ; X64-NEXT:    movq (%rdi), %rcx
 ; X64-NEXT:    orq %rax, %rcx

 ; X64-RETPOLINE-NEXT:    popq %rcx
 ; X64-RETPOLINE-NEXT:    retq
 entry:
   %fp = load i32 ()*, i32 ()** %ptr
   %v = call i32 %fp()
   ret i32 %v
 }
 
-define i32 @test_indirect_tail_call(i32 ()** %ptr) nounwind {
+define i32 @test_indirect_tail_call(i32 ()** %ptr) nounwind speculative_load_hardening {
 ; X64-LABEL: test_indirect_tail_call:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    movq %rsp, %rax
 ; X64-NEXT:    movq $-1, %rcx
 ; X64-NEXT:    sarq $63, %rax
 ; X64-NEXT:    movq (%rdi), %rcx
 ; X64-NEXT:    orq %rax, %rcx
 ; X64-NEXT:    shlq $47, %rax

 ; X64-RETPOLINE-NEXT:    orq %rax, %rsp
 ; X64-RETPOLINE-NEXT:    jmp __llvm_retpoline_r11 # TAILCALL
 entry:
   %fp = load i32 ()*, i32 ()** %ptr
   %v = tail call i32 %fp()
   ret i32 %v
 }
 
-define i32 @test_indirect_call_global() nounwind {
+define i32 @test_indirect_call_global() nounwind speculative_load_hardening {
 ; X64-LABEL: test_indirect_call_global:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %rax
 ; X64-NEXT:    movq %rsp, %rax
 ; X64-NEXT:    movq $-1, %rcx
 ; X64-NEXT:    sarq $63, %rax
 ; X64-NEXT:    movq {{.*}}(%rip), %rcx
 ; X64-NEXT:    orq %rax, %rcx

 ; X64-RETPOLINE-NEXT:    popq %rcx
 ; X64-RETPOLINE-NEXT:    retq
 entry:
   %fp = load i32 ()*, i32 ()** @global_fnptr
   %v = call i32 %fp()
   ret i32 %v
 }
 
-define i32 @test_indirect_tail_call_global() nounwind {
+define i32 @test_indirect_tail_call_global() nounwind speculative_load_hardening {
 ; X64-LABEL: test_indirect_tail_call_global:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    movq %rsp, %rax
 ; X64-NEXT:    movq $-1, %rcx
 ; X64-NEXT:    sarq $63, %rax
 ; X64-NEXT:    movq {{.*}}(%rip), %rcx
 ; X64-NEXT:    orq %rax, %rcx
 ; X64-NEXT:    shlq $47, %rax

 ; X64-RETPOLINE-NEXT:    orq %rax, %rsp
 ; X64-RETPOLINE-NEXT:    jmp __llvm_retpoline_r11 # TAILCALL
 entry:
   %fp = load i32 ()*, i32 ()** @global_fnptr
   %v = tail call i32 %fp()
   ret i32 %v
 }
 
-define i32 @test_indirectbr(i8** %ptr) nounwind {
+define i32 @test_indirectbr(i8** %ptr) nounwind speculative_load_hardening {
 ; X64-LABEL: test_indirectbr:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    movq %rsp, %rcx
 ; X64-NEXT:    movq $-1, %rax
 ; X64-NEXT:    sarq $63, %rcx
 ; X64-NEXT:    movq (%rdi), %rax
 ; X64-NEXT:    orq %rcx, %rax
 ; X64-NEXT:    jmpq *%rax

 
 bb2:
   ret i32 13
 
 bb3:
   ret i32 42
 }
 
-define i32 @test_indirectbr_global(i32 %idx) nounwind {
+define i32 @test_indirectbr_global(i32 %idx) nounwind speculative_load_hardening {
 ; X64-LABEL: test_indirectbr_global:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    movq %rsp, %rcx
 ; X64-NEXT:    movq $-1, %rax
 ; X64-NEXT:    sarq $63, %rcx
 ; X64-NEXT:    movslq %edi, %rax
 ; X64-NEXT:    movq global_blockaddrs(,%rax,8), %rax
 ; X64-NEXT:    orq %rcx, %rax
bb2:
   ret i32 13
 
 bb3:
   ret i32 42
 }
 
 ; This function's switch is crafted to trigger jump-table lowering in the x86
 ; backend so that we can test how the exact jump table lowering behaves.
-define i32 @test_switch_jumptable(i32 %idx) nounwind {
+define i32 @test_switch_jumptable(i32 %idx) nounwind speculative_load_hardening {
 ; X64-LABEL: test_switch_jumptable:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    movq %rsp, %rcx
 ; X64-NEXT:    movq $-1, %rax
 ; X64-NEXT:    sarq $63, %rcx
 ; X64-NEXT:    cmpl $3, %edi
 ; X64-NEXT:    ja .LBB6_2
 ; X64-NEXT:  # %bb.1: # %entry

llvm/test/CodeGen/X86/speculative-load-hardening.ll

 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -x86-speculative-load-hardening | FileCheck %s --check-prefix=X64
-; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -x86-speculative-load-hardening -x86-slh-lfence | FileCheck %s --check-prefix=X64-LFENCE
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s --check-prefix=X64
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -x86-slh-lfence | FileCheck %s --check-prefix=X64-LFENCE
 ;
 ; FIXME: Add support for 32-bit and other EH ABIs.
 
 declare void @leak(i32 %v1, i32 %v2)
 
 declare void @sink(i32)
 
-define i32 @test_trivial_entry_load(i32* %ptr) {
+define i32 @test_trivial_entry_load(i32* %ptr) speculative_load_hardening {
 ; X64-LABEL: test_trivial_entry_load:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    movq %rsp, %rcx
 ; X64-NEXT:    movq $-1, %rax
 ; X64-NEXT:    sarq $63, %rcx
 ; X64-NEXT:    movl (%rdi), %eax
 ; X64-NEXT:    orl %ecx, %eax
 ; X64-NEXT:    shlq $47, %rcx
 ; X64-NEXT:    orq %rcx, %rsp
 ; X64-NEXT:    retq
 ;
 ; X64-LFENCE-LABEL: test_trivial_entry_load:
 ; X64-LFENCE:       # %bb.0: # %entry
 ; X64-LFENCE-NEXT:    movl (%rdi), %eax
 ; X64-LFENCE-NEXT:    retq
 entry:
   %v = load i32, i32* %ptr
   ret i32 %v
 }
 
-define void @test_basic_conditions(i32 %a, i32 %b, i32 %c, i32* %ptr1, i32* %ptr2, i32** %ptr3) {
+define void @test_basic_conditions(i32 %a, i32 %b, i32 %c, i32* %ptr1, i32* %ptr2, i32** %ptr3) speculative_load_hardening {
 ; X64-LABEL: test_basic_conditions:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %r15
 ; X64-NEXT:    .cfi_def_cfa_offset 16
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    .cfi_def_cfa_offset 24
 ; X64-NEXT:    pushq %rbx
 ; X64-NEXT:    .cfi_def_cfa_offset 32
merge:
   %ptr2.idx3 = getelementptr i32, i32* %ptr2, i32 %secret7
   store i32 0, i32* %ptr2.idx3
   br label %exit
 
 exit:
   ret void
 }
 
-define void @test_basic_loop(i32 %a, i32 %b, i32* %ptr1, i32* %ptr2) nounwind {
+define void @test_basic_loop(i32 %a, i32 %b, i32* %ptr1, i32* %ptr2) nounwind speculative_load_hardening {
 ; X64-LABEL: test_basic_loop:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %rbp
 ; X64-NEXT:    pushq %r15
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    pushq %r12
 ; X64-NEXT:    pushq %rbx
 ; X64-NEXT:    movq %rsp, %rax
l.header:
   %i.next = add i32 %i, 1
   %i.cmp = icmp slt i32 %i.next, %b
   br i1 %i.cmp, label %l.header, label %exit
 
 exit:
   ret void
 }
 
-define void @test_basic_nested_loop(i32 %a, i32 %b, i32 %c, i32* %ptr1, i32* %ptr2) nounwind {
+define void @test_basic_nested_loop(i32 %a, i32 %b, i32 %c, i32* %ptr1, i32* %ptr2) nounwind speculative_load_hardening {
 ; X64-LABEL: test_basic_nested_loop:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %rbp
 ; X64-NEXT:    pushq %r15
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    pushq %r13
 ; X64-NEXT:    pushq %r12
 ; X64-NEXT:    pushq %rbx

 }
 
 declare i32 @__gxx_personality_v0(...)
 
 declare i8* @__cxa_allocate_exception(i64) local_unnamed_addr
 
 declare void @__cxa_throw(i8*, i8*, i8*) local_unnamed_addr
 
-define void @test_basic_eh(i32 %a, i32* %ptr1, i32* %ptr2) personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+define void @test_basic_eh(i32 %a, i32* %ptr1, i32* %ptr2) speculative_load_hardening personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
 ; X64-LABEL: test_basic_eh:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %rbp
 ; X64-NEXT:    .cfi_def_cfa_offset 16
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    .cfi_def_cfa_offset 24
 ; X64-NEXT:    pushq %rbx
 ; X64-NEXT:    .cfi_def_cfa_offset 32
lpad:
   call void @sink(i32 %leak)
   unreachable
 }
 
 declare void @sink_float(float)
 declare void @sink_double(double)
 
 ; Test direct and converting loads of floating point values.
-define void @test_fp_loads(float* %fptr, double* %dptr, i32* %i32ptr, i64* %i64ptr) nounwind {
+define void @test_fp_loads(float* %fptr, double* %dptr, i32* %i32ptr, i64* %i64ptr) nounwind speculative_load_hardening {
 ; X64-LABEL: test_fp_loads:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %r15
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    pushq %r12
 ; X64-NEXT:    pushq %rbx
 ; X64-NEXT:    pushq %rax
 ; X64-NEXT:    movq %rsp, %rax

 declare void @sink_v4f32(<4 x float>)
 declare void @sink_v2f64(<2 x double>)
 declare void @sink_v16i8(<16 x i8>)
 declare void @sink_v8i16(<8 x i16>)
 declare void @sink_v4i32(<4 x i32>)
 declare void @sink_v2i64(<2 x i64>)
 
 ; Test loads of vectors.
-define void @test_vec_loads(<4 x float>* %v4f32ptr, <2 x double>* %v2f64ptr, <16 x i8>* %v16i8ptr, <8 x i16>* %v8i16ptr, <4 x i32>* %v4i32ptr, <2 x i64>* %v2i64ptr) nounwind {
+define void @test_vec_loads(<4 x float>* %v4f32ptr, <2 x double>* %v2f64ptr, <16 x i8>* %v16i8ptr, <8 x i16>* %v8i16ptr, <4 x i32>* %v4i32ptr, <2 x i64>* %v2i64ptr) nounwind speculative_load_hardening {
 ; X64-LABEL: test_vec_loads:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %r15
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    pushq %r13
 ; X64-NEXT:    pushq %r12
 ; X64-NEXT:    pushq %rbx
 ; X64-NEXT:    movq %rsp, %rax
entry:
   call void @sink_v8i16(<8 x i16> %x4)
   %x5 = load <4 x i32>, <4 x i32>* %v4i32ptr
   call void @sink_v4i32(<4 x i32> %x5)
   %x6 = load <2 x i64>, <2 x i64>* %v2i64ptr
   call void @sink_v2i64(<2 x i64> %x6)
   ret void
 }
 
-define void @test_deferred_hardening(i32* %ptr1, i32* %ptr2, i32 %x) nounwind {
+define void @test_deferred_hardening(i32* %ptr1, i32* %ptr2, i32 %x) nounwind speculative_load_hardening {
 ; X64-LABEL: test_deferred_hardening:
 ; X64:       # %bb.0: # %entry
 ; X64-NEXT:    pushq %r14
 ; X64-NEXT:    pushq %rbx
 ; X64-NEXT:    pushq %rax
 ; X64-NEXT:    movq %rsp, %rax
 ; X64-NEXT:    movq %rsi, %r14
 ; X64-NEXT:    movq %rdi, %rbx

llvm/test/Transforms/Inline/attributes.ll

 define i32 @sanitize_memory_callee(i32 %i) sanitize_memory {
   ret i32 %i
 }
 
 define i32 @safestack_callee(i32 %i) safestack {
   ret i32 %i
 }
 
+define i32 @slh_callee(i32 %i) speculative_load_hardening {
+  ret i32 %i
+}
+
 define i32 @alwaysinline_callee(i32 %i) alwaysinline {
   ret i32 %i
 }
 
 define i32 @alwaysinline_sanitize_address_callee(i32 %i) alwaysinline sanitize_address {
   ret i32 %i
 }
 
define i32 @test_safestack(i32 %arg) safestack {
   %x3 = call i32 @alwaysinline_callee(i32 %x2)
   %x4 = call i32 @alwaysinline_safestack_callee(i32 %x3)
   ret i32 %x4
 ; CHECK-LABEL: @test_safestack(
 ; CHECK-NEXT: @noattr_callee
 ; CHECK-NEXT: ret i32
 }
 
+; Can inline a normal function into an SLH'ed function.
+define i32 @test_caller_slh(i32 %i) speculative_load_hardening {
+; CHECK-LABEL: @test_caller_slh(
+; CHECK-SAME: ) [[SLH:.*]] {
+; CHECK-NOT: call
+; CHECK: ret i32
+entry:
+  %callee = call i32 @noattr_callee(i32 %i)
+  ret i32 %callee
+}
+
+; Can inline a SLH'ed function into a normal one, propagating SLH.
+define i32 @test_callee_slh(i32 %i) {
+; CHECK-LABEL: @test_callee_slh(
+; CHECK-SAME: ) [[SLH:.*]] {
+; CHECK-NOT: call
+; CHECK: ret i32
+entry:
+  %callee = call i32 @slh_callee(i32 %i)
+  ret i32 %callee
+}
+
 ; Check that a function doesn't get inlined if target-cpu strings don't match
 ; exactly.
 define i32 @test_target_cpu_callee0(i32 %i) "target-cpu"="corei7" {
   ret i32 %i
 }
 
 define i32 @test_target_cpu0(i32 %i) "target-cpu"="corei7" {
   %1 = call i32 @test_target_cpu_callee0(i32 %i)

 ; attribute.
 define i32 @test_null-pointer-is-valid2(i32 %i) "null-pointer-is-valid"="true" {
   %1 = call i32 @null-pointer-is-valid_callee2(i32 %i)
   ret i32 %1
 ; CHECK: @test_null-pointer-is-valid2(i32 %i) [[NULLPOINTERISVALID]] {
 ; CHECK-NEXT: ret i32
 }
 
+; CHECK: attributes [[SLH]] = { speculative_load_hardening }
 ; CHECK: attributes [[FPMAD_FALSE]] = { "less-precise-fpmad"="false" }
 ; CHECK: attributes [[FPMAD_TRUE]] = { "less-precise-fpmad"="true" }
 ; CHECK: attributes [[NOIMPLICITFLOAT]] = { noimplicitfloat }
 ; CHECK: attributes [[NOUSEJUMPTABLES]] = { "no-jump-tables"="true" }
 ; CHECK: attributes [[NULLPOINTERISVALID]] = { "null-pointer-is-valid"="true" }