[MIPS] Don't crash on unsized extern types with -mgpopt

[arichardson]

Summary

This fixes an assertion when building the FreeBSD MIPS64 kernel.

[sdardis]

I've seen this patch in the CHERI fork, thanks for upstreaming it. Some nits inlined and can you use update_llc_test_checks.py to generate the CHECK lines?

Thanks.

lib/Target/Mips/MipsTargetObjectFile.cpp

140

Change this to: "It is possible that the type of the global is unsized, i.e. a declaration of a extern struct. In this case don't presume it is in the small data section. This happens e.g. when building the FreeBSD kernel."

test/CodeGen/Mips/unsized-global.ll

3

Add -mattr=+noabicalls here.

5–8

This metadata can be removed.

14

This line can be removed.

15

You can drop the 'local_unnamed_addr #0" here.

15–33

This llvm-ir can all be simplified to:

define %struct.a* @d() {
entry:
  ret %struct.a* @b
}

35–41

All of this can be dropped as well.

[arichardson]

Addressed review comments

[sdardis]

LGTM.

lib/Target/Mips/MipsTargetObjectFile.cpp

if (!ExternSData && ((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
                        GVA->hasCommonLinkage()))
     return false;
 
   // Enforce -membedded-data.
   if (EmbeddedData && GVA->isConstant())
     return false;
 
   Type *Ty = GVA->getValueType();
+
+  // It is possible that the type of the global is unsized, i.e. a declaration
+  // of a extern struct. In this case don't presume it is in the small data
+  // section. This happens e.g. when building the FreeBSD kernel.
+  if (!Ty->isSized())
+    return false;
+
   return IsInSmallSection(
       GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
 }
 
 MCSection *MipsTargetObjectFile::SelectSectionForGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
   // sections?

test/CodeGen/Mips/unsized-global.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; Check that -mgpopt doesn't crash on unsized externals
+; RUN: llc -mtriple=mips64-unknown-freebsd -mattr=+noabicalls -target-abi n64 -mgpopt -o - %s | FileCheck %s
+
+%struct.a = type opaque
+
+@b = external global %struct.a, align 1
+
+; Function Attrs: norecurse nounwind readnone
+define %struct.a* @d() {
+; CHECK-LABEL: d:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    lui $1, %highest(b)
+; CHECK-NEXT:    daddiu $1, $1, %higher(b)
+; CHECK-NEXT:    dsll $1, $1, 16
+; CHECK-NEXT:    daddiu $1, $1, %hi(b)
+; CHECK-NEXT:    dsll $1, $1, 16
+; CHECK-NEXT:    jr $ra
+; CHECK-NEXT:    daddiu $2, $1, %lo(b)
+entry:
+  ret %struct.a* @b
+}