[AArch64] [MinGW] Allow enabling SEH exceptions

[mstorsjo]

Summary

The default for mingw/aarch64 still is dwarf, but SEH exceptions can now be enabled optionally for the MinGW target.

Once things have settled and this works fine in practice, the default can be switched from dwarf to SEH. Or is this unnecessary churn and we should just keep off this until the default can be changed?

[rnk]

lgtm I think it's worth making this work incrementally like this.

lib/MC/MCObjectFileInfo.cpp

void MCObjectFileInfo::initCOFFMCObjectFileInfo(const Triple &T) {
   DataSection = Ctx->getCOFFSection(
       ".data", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ |
                    COFF::IMAGE_SCN_MEM_WRITE,
       SectionKind::getData());
   ReadOnlySection = Ctx->getCOFFSection(
       ".rdata", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA | COFF::IMAGE_SCN_MEM_READ,
       SectionKind::getReadOnly());
 
-  if (T.getArch() == Triple::x86_64) {
+  if (T.getArch() == Triple::x86_64 || T.getArch() == Triple::aarch64) {
     // On Windows 64 with SEH, the LSDA is emitted into the .xdata section
     LSDASection = nullptr;
   } else {
     LSDASection = Ctx->getCOFFSection(".gcc_except_table",
                                       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
                                           COFF::IMAGE_SCN_MEM_READ,
                                       SectionKind::getReadOnly());
   }

lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp

AArch64MCAsmInfoGNUCOFF::AArch64MCAsmInfoGNUCOFF() {
   Data64bitsDirective = "\t.xword\t";
 
   AlignmentIsInBytes = false;
   SupportsDebugInformation = true;
   CodePointerSize = 8;
 
   CommentString = "//";
   ExceptionsType = ExceptionHandling::DwarfCFI;
+  WinEHEncodingType = WinEH::EncodingType::Itanium;
 }

test/CodeGen/AArch64/wineh-mingw.ll

+; RUN: llc < %s -exception-model=wineh -mtriple=aarch64-pc-mingw32 | FileCheck %s -check-prefix=WINEH
+; RUN: llc < %s -exception-model=wineh -mtriple=aarch64-pc-mingw32 -filetype=obj | llvm-readobj -s | FileCheck %s -check-prefix=WINEH-SECTIONS
+
+; Check emission of eh handler and handler data
+declare i32 @_d_eh_personality(i32, i32, i64, i8*, i8*)
+declare void @_d_eh_resume_unwind(i8*)
+
+declare i32 @bar()
+
+define i32 @foo4() #0 personality i32 (i32, i32, i64, i8*, i8*)* @_d_eh_personality {
+entry:
+  %step = alloca i32, align 4
+  store i32 0, i32* %step
+  %tmp = load i32, i32* %step
+
+  %tmp1 = invoke i32 @bar()
+          to label %finally unwind label %landingpad
+
+finally:
+  store i32 1, i32* %step
+  br label %endtryfinally
+
+landingpad:
+  %landing_pad = landingpad { i8*, i32 }
+          cleanup
+  %tmp3 = extractvalue { i8*, i32 } %landing_pad, 0
+  store i32 2, i32* %step
+  call void @_d_eh_resume_unwind(i8* %tmp3)
+  unreachable
+
+endtryfinally:
+  %tmp10 = load i32, i32* %step
+  ret i32 %tmp10
+}
+; WINEH-LABEL: foo4:
+; WINEH: .seh_proc foo4
+; WINEH: .seh_handler _d_eh_personality, @unwind, @except
+; WINEH: ret
+; WINEH: .section .xdata,"dr"
+; WINEH-NEXT: .seh_handlerdata
+; WINEH-NEXT: .text
+; WINEH-NEXT: .seh_endproc
+; WINEH: .section .xdata,"dr"
+; WINEH-NEXT: .p2align 2
+; WINEH-NEXT: GCC_except_table0:
+
+; WINEH-SECTIONS: Name: .xdata
+; WINEH-SECTIONS-NOT: Name: .gcc_except_table