r284253 - Implement __stosb intrinsic as a volatile memset

[Albert Gutowski via cfe-commits]

Author: agutowski
Date: Fri Oct 14 12:33:05 2016
New Revision: 284253

URL: http://llvm.org/viewvc/llvm-project?rev=284253&view=rev
Log:
Implement __stosb intrinsic as a volatile memset

Summary: We need `__stosb` to be an intrinsic, because SecureZeroMemory function uses it without including intrin.h. Implementing it as a volatile memset is not consistent with MSDN specification, but it gives us target-independent IR while keeping the most important properties of `__stosb`.

Reviewers: rnk, hans, thakis, majnemer

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25334

Modified:
    cfe/trunk/include/clang/Basic/BuiltinsX86.def
    cfe/trunk/lib/CodeGen/CGBuiltin.cpp
    cfe/trunk/lib/Headers/intrin.h
    cfe/trunk/test/CodeGen/ms-intrinsics.c
    cfe/trunk/test/Headers/ms-intrin.cpp

Modified: cfe/trunk/include/clang/Basic/BuiltinsX86.def
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/BuiltinsX86.def?rev=284253&r1=284252&r2=284253&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/BuiltinsX86.def (original)
+++ cfe/trunk/include/clang/Basic/BuiltinsX86.def Fri Oct 14 12:33:05 2016
@@ -2041,6 +2041,8 @@ TARGET_HEADER_BUILTIN(__emulu, "ULLiUiUi
 
 TARGET_HEADER_BUILTIN(_AddressOfReturnAddress, "v*", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
 
+TARGET_HEADER_BUILTIN(__stosb, "vUc*Ucz", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+
 #undef BUILTIN
 #undef TARGET_BUILTIN
 #undef TARGET_HEADER_BUILTIN

Modified: cfe/trunk/lib/CodeGen/CGBuiltin.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGBuiltin.cpp?rev=284253&r1=284252&r2=284253&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGBuiltin.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGBuiltin.cpp Fri Oct 14 12:33:05 2016
@@ -7770,6 +7770,11 @@ Value *CodeGenFunction::EmitX86BuiltinEx
     Value *F = CGM.getIntrinsic(Intrinsic::addressofreturnaddress);
     return Builder.CreateCall(F);
   }
+  case X86::BI__stosb: {
+    // We treat __stosb as a volatile memset - it may not generate "rep stosb"
+    // instruction, but it will create a memset that won't be optimized away.
+    return Builder.CreateMemSet(Ops[0], Ops[1], Ops[2], 1, true);
+  }
   }
 }
 

Modified: cfe/trunk/lib/Headers/intrin.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Headers/intrin.h?rev=284253&r1=284252&r2=284253&view=diff
==============================================================================
--- cfe/trunk/lib/Headers/intrin.h (original)
+++ cfe/trunk/lib/Headers/intrin.h Fri Oct 14 12:33:05 2016
@@ -1024,11 +1024,6 @@ __movsw(unsigned short *__dst, unsigned
                         : "%edi", "%esi", "%ecx");
 }
 static __inline__ void __DEFAULT_FN_ATTRS
-__stosb(unsigned char *__dst, unsigned char __x, size_t __n) {
-  __asm__("rep stosb" : : "D"(__dst), "a"(__x), "c"(__n)
-                        : "%edi", "%ecx");
-}
-static __inline__ void __DEFAULT_FN_ATTRS
 __stosd(unsigned long *__dst, unsigned long __x, size_t __n) {
   __asm__("rep stosl" : : "D"(__dst), "a"(__x), "c"(__n)
                         : "%edi", "%ecx");

Modified: cfe/trunk/test/CodeGen/ms-intrinsics.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/ms-intrinsics.c?rev=284253&r1=284252&r2=284253&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/ms-intrinsics.c (original)
+++ cfe/trunk/test/CodeGen/ms-intrinsics.c Fri Oct 14 12:33:05 2016
@@ -14,6 +14,22 @@ typedef __SIZE_TYPE__ size_t;
 
 #include <intrin.h>
 
+#if defined(__i386__) || defined(__x86_64__)
+void test__stosb(unsigned char *Dest, unsigned char Data, size_t Count) {
+  return __stosb(Dest, Data, Count);
+}
+
+// CHECK-I386: define{{.*}}void @test__stosb
+// CHECK-I386:   tail call void @llvm.memset.p0i8.i32(i8* %Dest, i8 %Data, i32 %Count, i32 1, i1 true)
+// CHECK-I386:   ret void
+// CHECK-I386: }
+
+// CHECK-X64: define{{.*}}void @test__stosb
+// CHECK-X64:   tail call void @llvm.memset.p0i8.i64(i8* %Dest, i8 %Data, i64 %Count, i32 1, i1 true)
+// CHECK-X64:   ret void
+// CHECK-X64: }
+#endif
+
 void *test_ReturnAddress() {
   return _ReturnAddress();
 }

Modified: cfe/trunk/test/Headers/ms-intrin.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Headers/ms-intrin.cpp?rev=284253&r1=284252&r2=284253&view=diff
==============================================================================
--- cfe/trunk/test/Headers/ms-intrin.cpp (original)
+++ cfe/trunk/test/Headers/ms-intrin.cpp Fri Oct 14 12:33:05 2016
@@ -38,7 +38,6 @@ void f() {
   __movsd(0, 0, 0);
   __movsw(0, 0, 0);
 
-  __stosb(0, 0, 0);
   __stosd(0, 0, 0);
   __stosw(0, 0, 0);