Look through variables when computing relocations.

Given

bar = foo + 4
	.long bar

MC would eat the 4. GNU as includes it in the relocation. The rule seems to be
that a variable that defines a symbol is used in the relocation and one that
does not define a symbol is evaluated and the result included in the relocation.

Fixing this unfortunately required some other changes:

* Since the variable is now evaluated, it would prevent the ELF writer from
  noticing the weakref marker the elf streamer uses. This patch then replaces
  that with a VariantKind in MCSymbolRefExpr.

* Using VariantKind then requires us to look past other VariantKind to see

	.weakref	bar,foo
	call	bar@PLT

  doing this also fixes

	zed = foo +2
	call zed@PLT

  so that is a good thing.

* Looking past VariantKind means that the relocation selection has to use
  the fixup instead of the target.

This is a reboot of the previous fixes for MC. I will watch the sanitizer
buildbot and wait for a build before adding back the previous fixes.

llvm-svn: 204294

1 files changed, 1 insertions, 3 deletions

diff --git a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
index 217a51cea49..ddc1379e340 100644
--- a/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
+++ b/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCObjectWriter.cpp
@@ -88,9 +88,7 @@ unsigned SystemZObjectWriter::GetRelocType(const MCValue &Target,
                                            bool IsPCRel,
                                            bool IsRelocWithSymbol,
                                            int64_t Addend) const {
-  MCSymbolRefExpr::VariantKind Modifier = (Target.isAbsolute() ?
-                                           MCSymbolRefExpr::VK_None :
-                                           Target.getSymA()->getKind());
+  MCSymbolRefExpr::VariantKind Modifier = Fixup.getAccessVariant();
   unsigned Kind = Fixup.getKind();
   switch (Modifier) {
   case MCSymbolRefExpr::VK_None: