[PATCH] D25334: Implement __stosb intrinsic as a volatile memset

[Albert Gutowski via cfe-commits]

agutowski created this revision.
agutowski added reviewers: rnk, hans, thakis, majnemer.
agutowski added a subscriber: cfe-commits.

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.


https://reviews.llvm.org/D25334

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


Index: lib/Headers/intrin.h
===================================================================
--- lib/Headers/intrin.h
+++ lib/Headers/intrin.h
@@ -1148,11 +1148,6 @@
                         : "%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");
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -7599,7 +7599,20 @@
     HigherBits = Builder.CreateIntCast(HigherBits, ResType, IsSigned);
     return HigherBits;
   }
+
+  case X86::BI__stosb: {
+    // we treat __stosb as volatile memset  - it may not generate "rep stosb"
+    // instruction, but it will create a memset that won't be optimized away
+    const FunctionDecl *FD = E->getDirectCallee();
+    Address Dest = EmitPointerWithAlignment(E->getArg(0));
+    Value *ByteVal = EmitScalarExpr(E->getArg(1));
+    Value *SizeVal = EmitScalarExpr(E->getArg(2));
+    EmitNonNullArgCheck(RValue::get(Dest.getPointer()), E->getArg(0)->getType(),
+                        E->getArg(0)->getExprLoc(), FD, 0);
+    Builder.CreateMemSet(Dest, ByteVal, SizeVal, true);
+    return Dest.getPointer();
   }
+  }
 }
 
 
Index: include/clang/Basic/BuiltinsX86.def
===================================================================
--- include/clang/Basic/BuiltinsX86.def
+++ include/clang/Basic/BuiltinsX86.def
@@ -2071,6 +2071,8 @@
 TARGET_BUILTIN(__builtin_ia32_monitorx, "vv*UiUi", "", "mwaitx")
 TARGET_BUILTIN(__builtin_ia32_mwaitx, "vUiUiUi", "", "mwaitx")
 
+TARGET_HEADER_BUILTIN(__stosb, "vUc*Ucz", "nh", "intrin.h", ALL_MS_LANGUAGES, "")
+
 #undef BUILTIN
 #undef TARGET_BUILTIN
 #undef TARGET_HEADER_BUILTIN
Index: test/CodeGen/ms-intrinsics.c
===================================================================
--- test/CodeGen/ms-intrinsics.c
+++ test/CodeGen/ms-intrinsics.c
@@ -14,6 +14,22 @@
 
 #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_InterlockedExchangePointer(void * volatile *Target, void *Value) {
   return _InterlockedExchangePointer(Target, Value);
 }
Index: test/Headers/ms-intrin.cpp
===================================================================
--- test/Headers/ms-intrin.cpp
+++ test/Headers/ms-intrin.cpp
@@ -38,7 +38,6 @@
   __movsd(0, 0, 0);
   __movsw(0, 0, 0);
 
-  __stosb(0, 0, 0);
   __stosd(0, 0, 0);
   __stosw(0, 0, 0);
 


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