diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/DebugInfo/CodeView/SymbolRecord.h"
@@ -2497,6 +2498,84 @@
   if ((!IsDarwin || NParameters != 0) && NParameters != A.size())
     return Error(L, "Wrong number of arguments");
 
+  // Handles LOCAL directives in alternate macro mode.
+  std::string Buf;
+  if (AltMacroMode && Body.find("LOCAL ") != std::string::npos) {
+    std::size_t Pos = 0;
+    StringSet<> Locals;
+
+    // Checks if there are duplicate arguments to LOCAL directives
+    while (true) {
+      Pos = Body.find("LOCAL ", Pos);
+      if (Pos == std::string::npos)
+        break;
+      if (Pos > 0 && isalpha(Body[Pos - 1]))
+        continue;
+
+      std::size_t I = Pos + 6;
+      std::size_t E = Body.find('\n', I);
+      while (I < E) {
+        while (I < E && !isIdentifierChar(Body[I]))
+          ++I;
+        std::size_t SymB = I;
+        while (I < E && isIdentifierChar(Body[I]))
+          ++I;
+        std::string Sym(Body.data() + SymB, I - SymB);
+        if (!Locals.insert(Sym).second)
+          return Error(
+              L, Sym + " was already used as an argument to a LOCAL directive");
+      }
+      Pos = E + 1;
+    }
+
+    Buf = std::string(Body);
+    Pos = 0;
+
+    // Replaces all the uses of the argument to a LOCAL directive with a unique
+    // name
+    while (true) {
+      Pos = Buf.find("LOCAL ", Pos);
+      if (Pos == std::string::npos)
+        break;
+      if (Pos > 0 && isalpha(Buf[Pos - 1]))
+        continue;
+
+      std::size_t I = Pos + 6;
+      std::size_t E = Buf.find('\n', I);
+      while (I < E) {
+        while (I < E && !isIdentifierChar(Buf[I]))
+          ++I;
+        std::size_t SymB = I;
+        while (I < E && isIdentifierChar(Buf[I]))
+          ++I;
+        std::string Sym(Buf.data() + SymB, I - SymB);
+        std::string LocalSym;
+        do {
+          static unsigned LocalCnt = 0;
+          LocalSym = Sym + std::to_string(LocalCnt++);
+        } while (getContext().lookupSymbol(LocalSym));
+
+        // Replace all the uses of the current argument
+        size_t SymI = E + 1;
+        while (true) {
+          SymI = Buf.find(Sym, SymI);
+          if (SymI == std::string::npos)
+            break;
+          std::size_t SymE = SymI + Sym.size();
+          if ((SymI > 0 && isIdentifierChar(Buf[SymI - 1])) ||
+              (SymE < Buf.size() && isIdentifierChar(Buf[SymE]))) {
+            SymI = SymE;
+            continue;
+          }
+          Buf = Buf.substr(0, SymI) + LocalSym + Buf.substr(SymE);
+          SymI += LocalSym.size();
+        }
+      }
+      Buf = Buf.substr(0, Pos) + Buf.substr(E + 1);
+    }
+    Body = Buf;
+  }
+
   // A macro without parameters is handled differently on Darwin:
   // gas accepts no arguments and does no substitutions
   while (!Body.empty()) {
diff --git a/llvm/test/MC/AsmParser/directive_local_alt_macro_mode.s b/llvm/test/MC/AsmParser/directive_local_alt_macro_mode.s
new file mode 100644
--- /dev/null
+++ b/llvm/test/MC/AsmParser/directive_local_alt_macro_mode.s
@@ -0,0 +1,42 @@
+// RUN: llvm-mc -triple i386 -filetype=asm %s | FileCheck %s
+// RUN: not llvm-mc -triple i386 -filetype=asm --defsym ERR=1 %s -o /dev/null 2>&1  | FileCheck --check-prefix=ERR %s
+
+.altmacro
+
+.macro write arg
+LOCAL x,y
+.set x, \arg
+.set y, \arg
+.set z, \arg
+LOCAL z
+.endm
+
+.macro err
+LOCAL x,y
+LOCAL x
+.endm
+
+
+.macro read
+mov x, %eax
+mov y, %ebx
+mov z, %ecx
+.endm
+
+
+write 16
+read
+.ifdef ERR
+err
+// ERR:[[#@LINE-1]]:4: error: x was already used as an argument to a LOCAL directive
+.endif
+
+
+// CHECK:      .set x0, 16
+// CHECK-NEXT: .set y1, 16
+// CHECK-NEXT: .set z, 16
+// CHECK-EMPTY:
+// CHECK-NEXT: movl x, %eax
+// CHECK-NEXT: movl y, %ebx
+// CHECK-NEXT: movl 16, %ecx
+