[clang] Fix inline builtin functions of an __asm__ renamed function with symbol prefixes

[mstorsjo]

Summary

If a function is renamed with __asm__, the name provided is the
exact symbol name, without any extra implicit symbol prefixes.
If the target does use symbol prefixes, the IR level symbol gets
an \01 prefix to indicate that it's a literal symbol name to be
taken as is.

When a builtin function is specialized by providing an inline
version of it, that inline function is named <funcname>.inline.

When the base function has been renamed due to __asm__, the inline
function ends up named <asmname>.inline. Up to this point,
things did work as expected before.

However, for targets with symbol prefixes, one codepath that produced
the combined name <asmname>.inline used the mangled asmname with
\01 prefix, while others didn't. This patch fixes this.

This fixes the combination of asm renamed builtin function, with
inline override of the function, on any target with symbol
prefixes (such as i386 windows and any Darwin target).

Alternatively, instead of reimplementing this piece of logic
here, should it try to call MangleContext::mangleName somehow?

[rnk]

clang/lib/CodeGen/CGExpr.cpp

5020

I think you can call CGM.getMangledName, but I might be wrong. It's worth doing if straightforward.

[mstorsjo]

clang/lib/CodeGen/CGExpr.cpp

5020

Thanks, that seems to work just great, and simplifies things nicely!

[mstorsjo]

Use CGM.getMangledName(), simplifying the code instead of complicating it further.

[mstorsjo]

This seems like a followup to D134362.

[rnk]

lgtm, thanks

clang/lib/CodeGen/CGExpr.cpp

 
 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";
 
-    auto *A = FD->getAttr<AsmLabelAttr>();
-    StringRef Ident = A ? A->getLabel() : FD->getName();
+    StringRef Ident = CGF.CGM.getMangledName(GD);
     std::string FDInlineName = (Ident + ".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 &&

clang/test/CodeGen/inline-builtin-asm-name.c

+// RUN: %clang_cc1 -triple i686-windows-gnu -emit-llvm -o - %s -disable-llvm-optzns | FileCheck %s
+
+// CHECK: call i32 @"\01_asm_func_name.inline"
+
+// CHECK: declare dso_local i32 @"\01_asm_func_name"(ptr noundef, i32 noundef, ptr noundef, ptr noundef)
+
+// CHECK: define internal i32 @"\01_asm_func_name.inline"
+
+// CHECK: call i32 @__mingw_vsnprintf
+
+// CHECK: declare dso_local i32 @__mingw_vsnprintf
+
+typedef unsigned int size_t;
+
+int __mingw_vsnprintf(char *_DstBuf, size_t _MaxCount, const char *_Format, __builtin_va_list _ArgList);
+
+// For the real use case, "_asm_func_name" is actually "___mingw_vsnprintf", but it's renamed in the testcase for disambiguation.
+int vsnprintf(char *__stream, size_t __n, const char *__format, __builtin_va_list __local_argv) __asm__("_asm_func_name");
+
+extern __inline__ __attribute__((__always_inline__, __gnu_inline__))
+int vsnprintf(char *__stream, size_t __n, const char *__format, __builtin_va_list __local_argv)
+{
+  return __mingw_vsnprintf(__stream, __n, __format, __local_argv);
+}
+
+void call(const char* fmt, ...) {
+  char buf[200];
+  __builtin_va_list ap;
+  __builtin_va_start(ap, fmt);
+  vsnprintf(buf, sizeof(buf), fmt, ap);
+  __builtin_va_end(ap);
+}