Index: lib/AST/Stmt.cpp
===================================================================
--- lib/AST/Stmt.cpp
+++ lib/AST/Stmt.cpp
@@ -632,6 +632,14 @@
 
       CurPtr = NameEnd+1;
       continue;
+    } else if (*Begin == 'v') {
+      // GCC accepts code staring with "%v", e. g. "%vpcmpestri" and transforms
+      // it into "vpcmpestri" instruction if target processor supports AVX and
+      // into "pcmpestri" otherwise.
+      if (C.getTargetInfo().hasFeature("avx"))
+        CurStringPiece = "v" + CurStringPiece;
+      CurStringPiece += EscapedChar;
+      continue;
     }
 
     DiagOffs = CurPtr-StrStart-1;
Index: test/CodeGen/avx-inline-asm.c
===================================================================
--- test/CodeGen/avx-inline-asm.c
+++ test/CodeGen/avx-inline-asm.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -target-feature +avx -emit-llvm -S %s -o - | FileCheck %s -check-prefix=CHECK-AVX
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -emit-llvm -S %s -o - | FileCheck %s
+
+void f(void* arg)
+{
+  __asm__ ("%vpcmpestri $0, (%1), %2"
+           : "=c"(arg)
+           : "r"(arg), "x"(arg));
+
+  // CHECK: pcmpestri
+  // CHECK-AVX: vpcmpestri
+}