[CodeGen] Sort .ctors in reverse on MinGW just like on other platforms

On MinGW targets, the .ctors section is always used (as opposed
to on ELF platforms, where .init_section is the default but
one can select using .ctors, with the -use-ctors option, or the
UseInitArray field in TargetOptions).

Apply the reverse ordering regardless of whether the caller has
set the UseInitArray flag for this target, as this target
unconditionally uses the .ctors section anyway.

For the CodeGen/X86/constructor.ll testcase, note how this now
produces the same output ordering as for ELF targets with -use-ctors.

This fixes llvm#55938.

Author: mstorsjo

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -2807,7 +2807,11 @@ void AsmPrinter::emitXXStructorList(const DataLayout &DL, const Constant *List,
 
   // Emit the structors in reverse order if we are using the .ctor/.dtor
   // initialization scheme.
-  if (!TM.Options.UseInitArray)
+  bool UseCtorSection = !TM.Options.UseInitArray;
+  // MinGW targets always use the .ctors section.
+  if (TM.getTargetTriple().isWindowsGNUEnvironment())
+    UseCtorSection = true;
+  if (UseCtorSection)
     std::reverse(Structors.begin(), Structors.end());
 
   const Align Align = DL.getPointerPrefAlignment();

llvm/test/CodeGen/X86/constructor.ll

@@ -77,14 +77,14 @@ entry:
 ; MCU-CTORS:         .section        .ctors,"aw",@progbits
 ; MCU-INIT-ARRAY:    .section        .init_array,"aw",@init_array
 
-; COFF-CTOR:		.section	.ctors.65520,"dw",associative,v
+; COFF-CTOR:		.section	.ctors,"dw"
 ; COFF-CTOR-NEXT:	.p2align	3
-; COFF-CTOR-NEXT:	.quad	g
+; COFF-CTOR-NEXT:	.quad	j
+; COFF-CTOR-NEXT:	.quad	i
+; COFF-CTOR-NEXT:	.quad	f
 ; COFF-CTOR-NEXT:	.section	.ctors.09980,"dw",associative,v
 ; COFF-CTOR-NEXT:	.p2align	3
 ; COFF-CTOR-NEXT:	.quad	h
-; COFF-CTOR-NEXT:	.section	.ctors,"dw"
+; COFF-CTOR-NEXT:	.section	.ctors.65520,"dw",associative,v
 ; COFF-CTOR-NEXT:	.p2align	3
-; COFF-CTOR-NEXT:	.quad	f
-; COFF-CTOR-NEXT:	.quad	i
-; COFF-CTOR-NEXT:	.quad	j
+; COFF-CTOR-NEXT:	.quad	g

llvm/test/MC/COFF/global_ctors_dtors.ll

@@ -56,10 +56,10 @@ define i32 @main() nounwind {
 ; WIN32-NOT: c_global_ctor
 ; WIN32: .section .CRT$XTX,"dr"
 ; WIN32: a_global_dtor
-; MINGW32: .section .ctors,"dw"
-; MINGW32: a_global_ctor
 ; MINGW32: .section .ctors,"dw",associative,{{_?}}b
 ; MINGW32: b_global_ctor
 ; MINGW32-NOT: c_global_ctor
+; MINGW32: .section .ctors,"dw"
+; MINGW32: a_global_ctor
 ; MINGW32: .section .dtors,"dw"
 ; MINGW32: a_global_dtor