[clang] ae80024 - [clang] Honor __attribute__((no_builtin("foo"))) on functions

[Stephen Long via cfe-commits]

Author: Stephen Long
Date: 2022-05-20T06:41:47-07:00
New Revision: ae80024fbe51339afabfa2ff43ae532356fa3c93

URL: https://github.com/llvm/llvm-project/commit/ae80024fbe51339afabfa2ff43ae532356fa3c93
DIFF: https://github.com/llvm/llvm-project/commit/ae80024fbe51339afabfa2ff43ae532356fa3c93.diff

LOG: [clang] Honor __attribute__((no_builtin("foo"))) on functions

Support for `__attribute__((no_builtin("foo")))` was added in https://reviews.llvm.org/D68028,
but builtins were still being used even when the attribute was placed on a function.

Reviewed By: hans

Differential Revision: https://reviews.llvm.org/D124701

Added: 
    clang/test/CodeGen/no-builtin-2.c

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/include/clang/Basic/AttrDocs.td
    clang/lib/CodeGen/CGExpr.cpp

Removed: 
    


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 69b5dc1dd1fd..5d1b12504f78 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -318,6 +318,10 @@ Attribute Changes in Clang
 - The ``__declspec(naked)`` attribute can no longer be written on a member
   function in Microsoft compatibility mode, matching the behavior of cl.exe.
 
+- Attribute ``no_builtin`` should now affect the generated code. It now disables
+  builtins (corresponding to the specific names listed in the attribute) in the
+  body of the function the attribute is on.
+
 Windows Support
 ---------------
 

diff  --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index d635da6b84b8..aedf11a70753 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -6000,9 +6000,6 @@ attribute `clang_builtin_alias`.
 def NoBuiltinDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
-.. Note:: This attribute is not yet fully implemented, it is validated but has
-          no effect on the generated code.
-
 The ``__attribute__((no_builtin))`` is similar to the ``-fno-builtin`` flag
 except it is specific to the body of a function. The attribute may also be
 applied to a virtual function but has no effect on the behavior of overriding

diff  --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index fbe1586001b1..3d7f13aed0ab 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -5034,7 +5034,16 @@ static CGCallee EmitDirectCallee(CodeGenFunction &CGF, GlobalDecl GD) {
   const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
 
   if (auto builtinID = FD->getBuiltinID()) {
+    std::string NoBuiltinFD = ("no-builtin-" + FD->getName()).str();
+    std::string NoBuiltins = "no-builtins";
     std::string FDInlineName = (FD->getName() + ".inline").str();
+
+    bool IsPredefinedLibFunction =
+        CGF.getContext().BuiltinInfo.isPredefinedLibFunction(builtinID);
+    bool HasAttributeNoBuiltin =
+        CGF.CurFn->getAttributes().hasFnAttr(NoBuiltinFD) ||
+        CGF.CurFn->getAttributes().hasFnAttr(NoBuiltins);
+
     // When directing calling an inline builtin, call it through it's mangled
     // name to make it clear it's not the actual builtin.
     if (CGF.CurFn->getName() != FDInlineName &&
@@ -5054,8 +5063,11 @@ static CGCallee EmitDirectCallee(CodeGenFunction &CGF, GlobalDecl GD) {
 
     // Replaceable builtins provide their own implementation of a builtin. If we
     // are in an inline builtin implementation, avoid trivial infinite
-    // recursion.
-    else
+    // recursion. Honor __attribute__((no_builtin("foo"))) or
+    // __attribute__((no_builtin)) on the current function unless foo is
+    // not a predefined library function which means we must generate the
+    // builtin no matter what.
+    else if (!IsPredefinedLibFunction || !HasAttributeNoBuiltin)
       return CGCallee::forBuiltin(builtinID, FD);
   }
 

diff  --git a/clang/test/CodeGen/no-builtin-2.c b/clang/test/CodeGen/no-builtin-2.c
new file mode 100644
index 000000000000..f236f29779e0
--- /dev/null
+++ b/clang/test/CodeGen/no-builtin-2.c
@@ -0,0 +1,63 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s
+
+typedef typeof(sizeof(0)) size_t;
+
+void bar(char *s);
+void *memset(void *s, int c, size_t n);
+void *memcpy(void *d, const void *s, size_t n);
+void *memmove(void *d, const void *s, size_t n);
+
+// CHECK: define{{.*}} void @foo1({{.*}}) #[[NO_NOBUILTIN:[0-9]+]]
+// CHECK:   call void @bar
+// CHECK:   call void @llvm.memset
+// CHECK:   call void @llvm.memcpy
+// CHECK:   call void @llvm.memmove
+void foo1(char *s, char *d, size_t n) {
+  bar(s);
+  memset(s, 0, n);
+  memcpy(d, s, n);
+  memmove(d, s, n);
+}
+
+// CHECK: define{{.*}} void @foo2({{.*}}) #[[NOBUILTIN_MEMSET:[0-9]+]]
+// CHECK:   call void @bar
+// CHECK:   {{.*}}call {{.*}} @memset
+// CHECK:   call void @llvm.memcpy
+// CHECK:   call void @llvm.memmove
+void foo2(char *s, char *d, size_t n) __attribute__((no_builtin("memset"))) {
+  bar(s);
+  memset(s, 1, n);
+  memcpy(d, s, n);
+  memmove(d, s, n);
+}
+
+// CHECK: define{{.*}} void @foo3({{.*}}) #[[NOBUILTIN_MEMSET_MEMCPY:[0-9]+]]
+// CHECK:   call void @bar
+// CHECK:   {{.*}}call {{.*}} @memset
+// CHECK:   {{.*}}call {{.*}} @memcpy
+// CHECK:   call void @llvm.memmove
+void foo3(char *s, char *d, size_t n) __attribute__((no_builtin("memset", "memcpy"))) {
+  bar(s);
+  memset(s, 2, n);
+  memcpy(d, s, n);
+  memmove(d, s, n);
+}
+
+// CHECK: define{{.*}} void @foo4({{.*}}) #[[NOBUILTINS:[0-9]+]]
+// CHECK:   call void @bar
+// CHECK:   {{.*}}call {{.*}} @memset
+// CHECK:   {{.*}}call {{.*}} @memcpy
+// CHECK:   {{.*}}call {{.*}} @memmove
+void foo4(char *s, char *d, size_t n) __attribute__((no_builtin)) {
+  bar(s);
+  memset(s, 2, n);
+  memcpy(d, s, n);
+  memmove(s, d, n);
+}
+
+// CHECK-NOT: attributes #[[NO_NOBUILTIN]] = {{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK-NOT: attributes #[[NO_NOBUILTIN]] = {{{.*}}"no-builtin-memcpy"{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK-NOT: attributes #[[NO_NOBUILTIN]] = {{{.*}}"no-builtins"{{.*}}}
+// CHECK:     attributes #[[NOBUILTIN_MEMSET]] = {{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK:     attributes #[[NOBUILTIN_MEMSET_MEMCPY]] = {{{.*}}"no-builtin-memcpy"{{.*}}"no-builtin-memset"{{.*}}}
+// CHECK:     attributes #[[NOBUILTINS]] = {{{.*}}"no-builtins"{{.*}}}