[clang][MinGW] Add asan DLL lib before other libs and objects

As stated in #61685, by
passing LLD the import lib of the asan DLL first, the asan DLL will be
listed as the first entry in the Import Directory Table, making it be
loaded first before other user DLLs. This allows asan to be initialized
as early as possible to increase its instrumentation coverage to include
other DLLs not built with asan.

This also avoids some false asan reports on `realloc` for memory
allocated during initialization of user DLLs being loaded earlier than
asan, because after this change they will be loaded later than asan.

Differential Revision: https://reviews.llvm.org/D146908

clang/lib/Driver/ToolChains/MinGW.cpp

@@ -200,6 +200,16 @@ void tools::MinGW::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddAllArgs(CmdArgs, options::OPT_u_Group);
   Args.AddLastArg(CmdArgs, options::OPT_Z_Flag);
 
+  // Add asan_dynamic as the first import lib before other libs. This allows
+  // asan to be initialized as early as possible to increase its instrumentation
+  // coverage to include other user DLLs which has not been built with asan.
+  if (Sanitize.needsAsanRt() && !Args.hasArg(options::OPT_nostdlib) &&
+      !Args.hasArg(options::OPT_nodefaultlibs)) {
+    // MinGW always links against a shared MSVCRT.
+    CmdArgs.push_back(
+        TC.getCompilerRTArgString(Args, "asan_dynamic", ToolChain::FT_Shared));
+  }
+
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
     if (Args.hasArg(options::OPT_shared) || Args.hasArg(options::OPT_mdll)) {
       CmdArgs.push_back(Args.MakeArgString(TC.GetFilePath("dllcrt2.o")));

clang/test/Driver/mingw-sanitizers.c

@@ -1,13 +1,20 @@
-// RUN: %clang -target i686-windows-gnu %s -### -fsanitize=address 2>&1 | FileCheck --check-prefix=ASAN-I686 %s
-// ASAN-I686: "{{.*}}libclang_rt.asan_dynamic-i386.dll.a"
-// ASAN-I686: "{{[^"]*}}libclang_rt.asan_dynamic_runtime_thunk-i386.a"
-// ASAN-I686: "--require-defined" "___asan_seh_interceptor"
-// ASAN-I686: "--whole-archive" "{{.*}}libclang_rt.asan_dynamic_runtime_thunk-i386.a" "--no-whole-archive"
-
-// RUN: %clang -target x86_64-windows-gnu %s -### -fsanitize=address 2>&1 | FileCheck --check-prefix=ASAN-X86_64 %s
-// ASAN-X86_64: "{{.*}}libclang_rt.asan_dynamic-x86_64.dll.a"
+// RUN: touch %t.a
+// RUN: %clang -target i686-windows-gnu %s -### -fsanitize=address -lcomponent %/t.a 2>&1 | FileCheck --check-prefixes=ASAN-ALL,ASAN-I686 -DINPUT=%/t.a %s
+// RUN: %clang -target x86_64-windows-gnu %s -### -fsanitize=address -lcomponent %/t.a 2>&1 | FileCheck --check-prefixes=ASAN-ALL,ASAN-X86_64 -DINPUT=%/t.a %s
+//
+// ASAN-ALL-NOT:"-l{{[^"]+"]}}"
+// ASAN-ALL-NOT:"[[INPUT]]"
+// ASAN-I686:   "{{[^"]*}}libclang_rt.asan_dynamic-i386.dll.a"
+// ASAN-X86_64: "{{[^"]*}}libclang_rt.asan_dynamic-x86_64.dll.a"
+// ASAN-ALL:    "-lcomponent"
+// ASAN-ALL:    "[[INPUT]]"
+// ASAN-I686:   "{{[^"]*}}libclang_rt.asan_dynamic-i386.dll.a"
+// ASAN-I686:   "{{[^"]*}}libclang_rt.asan_dynamic_runtime_thunk-i386.a"
+// ASAN-I686:   "--require-defined" "___asan_seh_interceptor"
+// ASAN-I686:   "--whole-archive" "{{[^"]*}}libclang_rt.asan_dynamic_runtime_thunk-i386.a" "--no-whole-archive"
+// ASAN-X86_64: "{{[^"]*}}libclang_rt.asan_dynamic-x86_64.dll.a"
 // ASAN-X86_64: "{{[^"]*}}libclang_rt.asan_dynamic_runtime_thunk-x86_64.a"
 // ASAN-X86_64: "--require-defined" "__asan_seh_interceptor"
-// ASAN-X86_64: "--whole-archive" "{{.*}}libclang_rt.asan_dynamic_runtime_thunk-x86_64.a" "--no-whole-archive"
+// ASAN-X86_64: "--whole-archive" "{{[^"]*}}libclang_rt.asan_dynamic_runtime_thunk-x86_64.a" "--no-whole-archive"
 
 // RUN: %clang -target x86_64-windows-gnu %s -### -fsanitize=vptr