diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -368,6 +368,8 @@
 X86 Support in Clang
 --------------------
 
+- Support ``-mharden-sls=[none|all|return|indirect-branch]`` for X86.
+
 DWARF Support in Clang
 ----------------------
 
diff --git a/clang/lib/Driver/ToolChains/Arch/X86.cpp b/clang/lib/Driver/ToolChains/Arch/X86.cpp
--- a/clang/lib/Driver/ToolChains/Arch/X86.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/X86.cpp
@@ -242,4 +242,22 @@
       Name = Name.substr(3);
     Features.push_back(Args.MakeArgString((IsNegative ? "-" : "+") + Name));
   }
+
+  // Enable/disable straight line speculation hardening.
+  if (Arg *A = Args.getLastArg(options::OPT_mharden_sls_EQ)) {
+    StringRef Scope = A->getValue();
+    if (Scope == "all") {
+      Features.push_back("+harden-sls-ind");
+      Features.push_back("+harden-sls-ret");
+    } else if (Scope == "none") {
+      Features.push_back("-harden-sls-ind");
+      Features.push_back("-harden-sls-ret");
+    } else if (Scope == "return") {
+      Features.push_back("+harden-sls-ret");
+    } else if (Scope == "indirect-branch") {
+      Features.push_back("+harden-sls-ind");
+    } else {
+      D.Diag(diag::err_invalid_sls_hardening) << Scope << A->getAsString(Args);
+    }
+  }
 }
diff --git a/clang/test/Driver/x86-target-features.c b/clang/test/Driver/x86-target-features.c
--- a/clang/test/Driver/x86-target-features.c
+++ b/clang/test/Driver/x86-target-features.c
@@ -304,3 +304,16 @@
 // RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mno-crc32 %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-CRC32 %s
 // CRC32: "-target-feature" "+crc32"
 // NO-CRC32: "-target-feature" "-crc32"
+
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=all %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-ALL %s
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=none %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-NONE %s
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=return %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-RET %s
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=indirect-branch %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-IND %s
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=none -mharden-sls=all %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-ALL %s
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=all -mharden-sls=none %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-NONE %s
+// RUN: %clang -target i386-unknown-linux-gnu -march=i386 -mharden-sls=return,indirect-branch %s -### -o %t.o 2>&1 | FileCheck -check-prefix=SLS-BAD %s
+// SLS-RET: "-target-feature" "+harden-sls-ret"
+// SLS-IND: "-target-feature" "+harden-sls-ind"
+// SLS-ALL: "-target-feature" "+harden-sls-ind" "-target-feature" "+harden-sls-ret"
+// SLS-NONE: "-target-feature" "-harden-sls-ind" "-target-feature" "-harden-sls-ret"
+// SLS-BAD: invalid sls hardening option '{{[^']+}}' in '-mharden-sls=
diff --git a/llvm/lib/Target/X86/X86.td b/llvm/lib/Target/X86/X86.td
--- a/llvm/lib/Target/X86/X86.td
+++ b/llvm/lib/Target/X86/X86.td
@@ -382,6 +382,17 @@
           "Use an instruction sequence for taking the address of a global "
           "that allows a memory tag in the upper address bits.">;
 
+// Control codegen mitigation against Straight Line Speculation vulnerability.
+def FeatureHardenSlsRet
+    : SubtargetFeature<
+          "harden-sls-ret", "HardenSlsRet", "true",
+          "Harden against straight line speculation across RET instructions.">;
+
+def FeatureHardenSlsInd
+    : SubtargetFeature<
+          "harden-sls-ind", "HardenSlsInd", "true",
+          "Harden against straight line speculation across indirect JMP instructions.">;
+
 //===----------------------------------------------------------------------===//
 // X86 Subtarget Tuning features
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.h b/llvm/lib/Target/X86/X86AsmPrinter.h
--- a/llvm/lib/Target/X86/X86AsmPrinter.h
+++ b/llvm/lib/Target/X86/X86AsmPrinter.h
@@ -131,10 +131,7 @@
 
   void emitInstruction(const MachineInstr *MI) override;
 
-  void emitBasicBlockEnd(const MachineBasicBlock &MBB) override {
-    AsmPrinter::emitBasicBlockEnd(MBB);
-    SMShadowTracker.emitShadowPadding(*OutStreamer, getSubtargetInfo());
-  }
+  void emitBasicBlockEnd(const MachineBasicBlock &MBB) override;
 
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        const char *ExtraCode, raw_ostream &O) override;
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
--- a/llvm/lib/Target/X86/X86AsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -336,6 +336,28 @@
   }
 }
 
+void X86AsmPrinter::emitBasicBlockEnd(const MachineBasicBlock &MBB) {
+  AsmPrinter::emitBasicBlockEnd(MBB);
+  if (Subtarget->hardenSlsRet() || Subtarget->hardenSlsInd()) {
+    auto I = MBB.getLastNonDebugInstr();
+    if (I != MBB.end()) {
+      const MCInstrDesc &Desc = I->getDesc();
+      auto IsIndirectTailCall = [I, &Desc]() {
+        return Desc.isCall() && Desc.isReturn() && Desc.isBarrier() &&
+               !I->getOperand(0).isGlobal();
+      };
+      if ((Subtarget->hardenSlsRet() && Desc.isReturn() && !Desc.isCall()) ||
+          (Subtarget->hardenSlsInd() &&
+           (Desc.isIndirectBranch() || IsIndirectTailCall()))) {
+        MCInst TmpInst;
+        TmpInst.setOpcode(X86::INT3);
+        EmitToStreamer(*OutStreamer, TmpInst);
+      }
+    }
+  }
+  SMShadowTracker.emitShadowPadding(*OutStreamer, getSubtargetInfo());
+}
+
 void X86AsmPrinter::PrintMemReference(const MachineInstr *MI, unsigned OpNo,
                                       raw_ostream &O, const char *Modifier) {
   assert(isMem(*MI, OpNo) && "Invalid memory reference!");
diff --git a/llvm/test/CodeGen/X86/speculation-hardening-sls.ll b/llvm/test/CodeGen/X86/speculation-hardening-sls.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/CodeGen/X86/speculation-hardening-sls.ll
@@ -0,0 +1,97 @@
+; RUN: llc -mattr=harden-sls-ret -verify-machineinstrs -mtriple=x86_64-unknown-unknown < %s | FileCheck %s -check-prefixes=CHECK,RET
+; RUN: llc -mattr=harden-sls-ind -verify-machineinstrs -mtriple=x86_64-unknown-unknown < %s | FileCheck %s -check-prefixes=CHECK,IND
+
+define dso_local i32 @double_return(i32 %a, i32 %b) local_unnamed_addr {
+; CHECK-LABEL: double_return:
+; CHECK:         jle
+; CEHCK-NOT:     int3
+; CHECK:         retq
+; RET-NEXT:      int3
+; IND-NOT:       int3
+; CHECK:         retq
+; RET-NEXT:      int3
+; IND-NOT:       int3
+entry:
+  %cmp = icmp sgt i32 %a, 0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  %div = sdiv i32 %a, %b
+  ret i32 %div
+
+if.else:                                          ; preds = %entry
+  %div1 = sdiv i32 %b, %a
+  ret i32 %div1
+}
+
+@__const.indirect_branch.ptr = private unnamed_addr constant [2 x i8*] [i8* blockaddress(@indirect_branch, %return), i8* blockaddress(@indirect_branch, %l2)], align 8
+
+; Function Attrs: norecurse nounwind readnone
+define dso_local i32 @indirect_branch(i32 %a, i32 %b, i32 %i) {
+; CHECK-LABEL: indirect_branch:
+; CHECK:         jmpq *
+; RET-NOT:       int3
+; IND-NEXT:      int3
+; CHECK:         retq
+; RET-NEXT:      int3
+; IND-NOT:       int3
+; CHECK:         retq
+; RET-NEXT:      int3
+; IND-NOT:       int3
+entry:
+  %idxprom = sext i32 %i to i64
+  %arrayidx = getelementptr inbounds [2 x i8*], [2 x i8*]* @__const.indirect_branch.ptr, i64 0, i64 %idxprom
+  %0 = load i8*, i8** %arrayidx, align 8
+  indirectbr i8* %0, [label %return, label %l2]
+
+l2:                                               ; preds = %entry
+  br label %return
+
+return:                                           ; preds = %entry, %l2
+  %retval.0 = phi i32 [ 1, %l2 ], [ 0, %entry ]
+  ret i32 %retval.0
+}
+
+define i32 @asmgoto() {
+; CHECK-LABEL: asmgoto:
+; CHECK:       # %bb.0: # %entry
+; CHECK:         jmp .L
+; CEHCK-NOT:     int3
+; CHECK:         retq
+; RET-NEXT:      int3
+; IND-NOT:       int3
+; CHECK:         retq
+; RET-NEXT:      int3
+; IND-NOT:       int3
+entry:
+  callbr void asm sideeffect "jmp $0", "X"(i8* blockaddress(@asmgoto, %d))
+            to label %asm.fallthrough [label %d]
+     ; The asm goto above produces a direct branch:
+
+asm.fallthrough:               ; preds = %entry
+  ret i32 0
+
+d:                             ; preds = %asm.fallthrough, %entry
+  ret i32 1
+}
+
+define void @bar(void ()* %0) {
+; CHECK-LABEL: bar:
+; CHECK:         jmpq *
+; RET-NOT:       int3
+; IND-NEXT:      int3
+; CEHCK-NOT:     ret
+  tail call void %0()
+  ret void
+}
+
+declare dso_local void @foo()
+
+define dso_local void @bar2() {
+; CHECK-LABEL: bar2:
+; CHECK:         jmp foo
+; CHECK-NOT:     int3
+; CEHCK-NOT:     ret
+  tail call void @foo()
+  ret void
+}