diff --git a/llvm/include/llvm/MC/MCExpr.h b/llvm/include/llvm/MC/MCExpr.h
index 11da711ab9ca..d5a68be3ec65 100644
--- a/llvm/include/llvm/MC/MCExpr.h
+++ b/llvm/include/llvm/MC/MCExpr.h
@@ -105,6 +105,13 @@ public:
   bool EvaluateAsRelocatable(MCValue &Res, const MCAsmLayout *Layout,
                              const MCFixup *Fixup) const;
 
+  /// \brief Try to evaluate the expression to the form (a - b + constant) where
+  /// neither a nor b are variables.
+  ///
+  /// This is a more aggressive variant of EvaluateAsRelocatable. The intended
+  /// use is for when relocations are not available, like the .size directive.
+  bool evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const;
+
   /// FindAssociatedSection - Find the "associated section" for this expression,
   /// which is currently defined as the absolute section for constants, or
   /// otherwise the section associated with the first defined symbol in the
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 6345bd534171..857eafc0b7e4 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -188,7 +188,7 @@ const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
 
   const MCExpr *Expr = Symbol.getVariableValue();
   MCValue Value;
-  if (!Expr->EvaluateAsRelocatable(Value, this, nullptr))
+  if (!Expr->evaluateAsValue(Value, *this))
     llvm_unreachable("Invalid Expression");
 
   const MCSymbolRefExpr *RefB = Value.getSymB();
diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
index 7508ef671233..8a64403362c0 100644
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -584,7 +584,15 @@ bool MCExpr::EvaluateAsRelocatable(MCValue &Res,
                                    false);
 }
 
-static bool canExpand(const MCSymbol &Sym, const MCAssembler *Asm) {
+bool MCExpr::evaluateAsValue(MCValue &Res, const MCAsmLayout &Layout) const {
+  MCAssembler *Assembler = &Layout.getAssembler();
+  return EvaluateAsRelocatableImpl(Res, Assembler, &Layout, nullptr, nullptr,
+                                   true);
+}
+
+static bool canExpand(const MCSymbol &Sym, const MCAssembler *Asm, bool InSet) {
+  if (InSet)
+    return true;
   if (!Asm)
     return false;
   const MCSymbolData &SD = Asm->getSymbolData(Sym);
@@ -613,10 +621,11 @@ bool MCExpr::EvaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
 
     // Evaluate recursively if this is a variable.
     if (Sym.isVariable() && SRE->getKind() == MCSymbolRefExpr::VK_None &&
-        canExpand(Sym, Asm)) {
+        canExpand(Sym, Asm, InSet)) {
+      bool IsMachO = SRE->hasSubsectionsViaSymbols();
       if (Sym.getVariableValue()->EvaluateAsRelocatableImpl(
-              Res, Asm, Layout, Fixup, Addrs, true)) {
-        if (!SRE->hasSubsectionsViaSymbols())
+              Res, Asm, Layout, Fixup, Addrs, InSet || IsMachO)) {
+        if (!IsMachO)
           return true;
 
         const MCSymbolRefExpr *A = Res.getSymA();
diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index c519a9d6d5e8..c6bc81ddc564 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -175,6 +175,8 @@ public:
                                               const MCFragment &FB, bool InSet,
                                               bool IsPCRel) const override;
 
+  bool isWeak(const MCSymbolData &SD) const override;
+
   void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
                         const MCFragment *Fragment, const MCFixup &Fixup,
                         MCValue Target, bool &IsPCRel,
@@ -661,6 +663,12 @@ bool WinCOFFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
                                                                 InSet, IsPCRel);
 }
 
+bool WinCOFFObjectWriter::isWeak(const MCSymbolData &SD) const {
+  // FIXME: this is for PR23025. Write a good description on
+  // why this is needed.
+  return SD.isExternal();
+}
+
 void WinCOFFObjectWriter::RecordRelocation(
     MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
     const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
diff --git a/llvm/test/MC/X86/expand-var.s b/llvm/test/MC/X86/expand-var.s
index b3311b4a8440..ef62d8a260fa 100644
--- a/llvm/test/MC/X86/expand-var.s
+++ b/llvm/test/MC/X86/expand-var.s
@@ -10,3 +10,9 @@ a:
         d = a
         .weak d
         .long d + (b - c)
+
+
+a2:
+        .weak b2
+        b2 = a2
+        c2 = b2 - a2