Index: test/CodeGen/inline-asm-attr.c
===================================================================
--- test/CodeGen/inline-asm-attr.c	(revision 0)
+++ test/CodeGen/inline-asm-attr.c	(revision 0)
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin10 -O3 -emit-llvm %s -o - | FileCheck %s
+
+__attribute__((const))
+static inline void **varptr(void) {
+    void *ptr;
+    asm("mov $0x12345678, %0" : "=r" (ptr));
+    return ptr;
+}
+static inline void *getvar(void) { return *varptr(); }
+static inline void setvar(void *value) { *varptr() = value; }
+
+void fn(void) {
+// CHECK: @fn
+// CHECK: entry
+// CHECK: tail call i8* asm 
+// CHECK: if.then
+// CHECK-NOT: tail call i8* asm 
+  if (getvar())
+    setvar(0);
+}
Index: lib/CodeGen/CGStmt.cpp
===================================================================
--- lib/CodeGen/CGStmt.cpp	(revision 155999)
+++ lib/CodeGen/CGStmt.cpp	(working copy)
@@ -1595,11 +1595,14 @@
   Constraints += InOutConstraints;
 
   // Clobbers
+  bool ClobbersOnlyRegisters = true;
   for (unsigned i = 0, e = S.getNumClobbers(); i != e; i++) {
     StringRef Clobber = S.getClobber(i)->getString();
 
     if (Clobber != "memory" && Clobber != "cc")
-    Clobber = Target.getNormalizedGCCRegisterName(Clobber);
+      Clobber = Target.getNormalizedGCCRegisterName(Clobber);
+    else
+      ClobbersOnlyRegisters = false;
 
     if (i != 0 || NumConstraints != 0)
       Constraints += ',';
@@ -1634,6 +1637,11 @@
   llvm::CallInst *Result = Builder.CreateCall(IA, Args);
   Result->addAttribute(~0, llvm::Attribute::NoUnwind);
 
+  // An inline asm can be marked readonly if it doesn't clobber memory/cc and it
+  // isn't volatile.
+  if (ClobbersOnlyRegisters && !S.isVolatile())
+    Result->addAttribute(~0, llvm::Attribute::ReadOnly);
+
   // Slap the source location of the inline asm into a !srcloc metadata on the
   // call.
   Result->setMetadata("srcloc", getAsmSrcLocInfo(S.getAsmString(), *this));