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

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).

Differential Revision: https://reviews.llvm.org/D137073

Author: mstorsjo

clang/lib/CodeGen/CGExpr.cpp

@@ -5014,8 +5014,7 @@ static CGCallee EmitDirectCallee(CodeGenFunction &CGF, GlobalDecl GD) {
     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 =

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

@@ -0,0 +1,32 @@
+// 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);
+}