[COFF] Fix assembly output of comdat sections without an attached symbol

[mstorsjo]

Summary

Since SVN r335286, the .xdata sections are produced without an attached symbol, which requires using a different syntax when printing assembly output.

Instead of the usual syntax of '.section <name>,"dr",discard,<symbol>', use '.section <name>,"dr"' + '.linkonce discard' (which is what GCC uses for all assembly output).

This fixes PR38254.

[rnk]

lgtm

lib/MC/MCSectionCOFF.cpp

void MCSectionCOFF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
   if (getCharacteristics() & COFF::IMAGE_SCN_MEM_SHARED)
     OS << 's';
   if ((getCharacteristics() & COFF::IMAGE_SCN_MEM_DISCARDABLE) &&
       !isImplicitlyDiscardable(SectionName))
     OS << 'D';
   OS << '"';
 
   if (getCharacteristics() & COFF::IMAGE_SCN_LNK_COMDAT) {
+    if (COMDATSymbol)
       OS << ",";
+    else
+      OS << "\n\t.linkonce\t";
     switch (Selection) {
       case COFF::IMAGE_COMDAT_SELECT_NODUPLICATES:
-        OS << "one_only,";
+        OS << "one_only";
         break;
       case COFF::IMAGE_COMDAT_SELECT_ANY:
-        OS << "discard,";
+        OS << "discard";
         break;
       case COFF::IMAGE_COMDAT_SELECT_SAME_SIZE:
-        OS << "same_size,";
+        OS << "same_size";
         break;
       case COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH:
-        OS << "same_contents,";
+        OS << "same_contents";
         break;
       case COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE:
-        OS << "associative,";
+        OS << "associative";
         break;
       case COFF::IMAGE_COMDAT_SELECT_LARGEST:
-        OS << "largest,";
+        OS << "largest";
         break;
       case COFF::IMAGE_COMDAT_SELECT_NEWEST:
-        OS << "newest,";
+        OS << "newest";
         break;
       default:
         assert(false && "unsupported COFF selection type");
         break;
     }
-    assert(COMDATSymbol);
+    if (COMDATSymbol) {
+      OS << ",";
       COMDATSymbol->print(OS, &MAI);
     }
+  }
   OS << '\n';
 }
 
 bool MCSectionCOFF::UseCodeAlign() const {
   return getKind().isText();
 }
 
 bool MCSectionCOFF::isVirtualSection() const {
   return getCharacteristics() & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA;
 }

test/CodeGen/X86/mingw-comdats-xdata.ll

+; RUN: llc -mtriple=x86_64-w64-windows-gnu < %s | FileCheck %s --check-prefix=GNU
+; RUN: llc -mtriple=x86_64-w64-windows-gnu < %s -filetype=obj | llvm-objdump - -headers | FileCheck %s --check-prefix=GNUOBJ
+
+; When doing GCC style comdats for MinGW, the .xdata sections don't have a normal comdat
+; symbol attached, which requires a bit of adjustments for the assembler output.
+
+; Generated with this C++ source:
+; int bar(int);
+; __declspec(selectany) int gv = 42;
+; inline int foo(int x) { try { return bar(x) + gv; } catch (...) { return 0; } }
+; int main() { return foo(1); }
+
+$_Z3fooi = comdat any
+
+$gv = comdat any
+
+@gv = weak_odr dso_local global i32 42, comdat, align 4
+
+; Function Attrs: norecurse uwtable
+define dso_local i32 @main() #0 {
+entry:
+  %call = tail call i32 @_Z3fooi(i32 1)
+  ret i32 %call
+}
+
+; GNU: main:
+
+; Function Attrs: inlinehint uwtable
+define linkonce_odr dso_local i32 @_Z3fooi(i32 %x) #1 comdat personality i8* bitcast (i32 (...)* @__gxx_personality_seh0 to i8*) {
+entry:
+  %call = invoke i32 @_Z3bari(i32 %x)
+          to label %invoke.cont unwind label %lpad
+
+invoke.cont:                                      ; preds = %entry
+  %0 = load i32, i32* @gv, align 4
+  %add = add nsw i32 %0, %call
+  br label %return
+
+lpad:                                             ; preds = %entry
+  %1 = landingpad { i8*, i32 }
+          catch i8* null
+  %2 = extractvalue { i8*, i32 } %1, 0
+  %3 = tail call i8* @__cxa_begin_catch(i8* %2) #3
+  tail call void @__cxa_end_catch()
+  br label %return
+
+return:                                           ; preds = %lpad, %invoke.cont
+  %retval.0 = phi i32 [ %add, %invoke.cont ], [ 0, %lpad ]
+  ret i32 %retval.0
+}
+
+; The .xdata section below doesn't have the usual comdat symbol attached, which requires
+; a different syntax for the assembly output.
+
+; GNU: .section        .text$_Z3fooi,"xr",discard,_Z3fooi
+; GNU: _Z3fooi:
+; GNU: .section        .xdata$_Z3fooi,"dr"
+; GNU: .linkonce       discard
+; GNU: GCC_except_table1:
+; GNU: .section        .data$gv,"dw",discard,gv
+; GNU: gv:
+; GNU: .long 42
+
+; Make sure the assembler puts the .xdata and .pdata in sections with the right
+; names.
+; GNUOBJ: .text$_Z3fooi
+; GNUOBJ: .xdata$_Z3fooi
+; GNUOBJ: .data$gv
+; GNUOBJ: .pdata$_Z3fooi
+
+declare dso_local i32 @_Z3bari(i32)
+
+declare dso_local i32 @__gxx_personality_seh0(...)
+
+declare dso_local i8* @__cxa_begin_catch(i8*) local_unnamed_addr
+
+declare dso_local void @__cxa_end_catch() local_unnamed_addr
+
+
+attributes #0 = { norecurse uwtable }
+attributes #1 = { inlinehint uwtable }
+attributes #3 = { nounwind }