Index: llvm/trunk/include/llvm/MC/MCExpr.h
===================================================================
--- llvm/trunk/include/llvm/MC/MCExpr.h
+++ llvm/trunk/include/llvm/MC/MCExpr.h
@@ -13,6 +13,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DataTypes.h"
+#include "llvm/Support/SMLoc.h"
 
 namespace llvm {
 class MCAsmInfo;
@@ -43,6 +44,7 @@
 
 private:
   ExprKind Kind;
+  SMLoc Loc;
 
   MCExpr(const MCExpr&) = delete;
   void operator=(const MCExpr&) = delete;
@@ -56,7 +58,7 @@
                           const SectionAddrMap *Addrs, bool InSet) const;
 
 protected:
-  explicit MCExpr(ExprKind Kind) : Kind(Kind) {}
+  explicit MCExpr(ExprKind Kind, SMLoc Loc) : Kind(Kind), Loc(Loc) {}
 
   bool evaluateAsRelocatableImpl(MCValue &Res, const MCAssembler *Asm,
                                  const MCAsmLayout *Layout,
@@ -68,6 +70,7 @@
   /// @{
 
   ExprKind getKind() const { return Kind; }
+  SMLoc getLoc() const { return Loc; }
 
   /// @}
   /// \name Utility Methods
@@ -132,7 +135,7 @@
   int64_t Value;
 
   explicit MCConstantExpr(int64_t Value)
-      : MCExpr(MCExpr::Constant), Value(Value) {}
+      : MCExpr(MCExpr::Constant, SMLoc()), Value(Value) {}
 
 public:
   /// \name Construction
@@ -289,7 +292,7 @@
   const MCSymbol *Symbol;
 
   explicit MCSymbolRefExpr(const MCSymbol *Symbol, VariantKind Kind,
-                           const MCAsmInfo *MAI);
+                           const MCAsmInfo *MAI, SMLoc Loc = SMLoc());
 
 public:
   /// \name Construction
@@ -300,7 +303,7 @@
   }
 
   static const MCSymbolRefExpr *create(const MCSymbol *Symbol, VariantKind Kind,
-                                       MCContext &Ctx);
+                                       MCContext &Ctx, SMLoc Loc = SMLoc());
   static const MCSymbolRefExpr *create(StringRef Name, VariantKind Kind,
                                        MCContext &Ctx);
 
@@ -346,7 +349,7 @@
   const MCExpr *Expr;
 
   MCUnaryExpr(Opcode Op, const MCExpr *Expr)
-      : MCExpr(MCExpr::Unary), Op(Op), Expr(Expr) {}
+      : MCExpr(MCExpr::Unary, SMLoc()), Op(Op), Expr(Expr) {}
 
 public:
   /// \name Construction
@@ -417,15 +420,17 @@
   Opcode Op;
   const MCExpr *LHS, *RHS;
 
-  MCBinaryExpr(Opcode Op, const MCExpr *LHS, const MCExpr *RHS)
-      : MCExpr(MCExpr::Binary), Op(Op), LHS(LHS), RHS(RHS) {}
+  MCBinaryExpr(Opcode Op, const MCExpr *LHS, const MCExpr *RHS,
+               SMLoc Loc = SMLoc())
+      : MCExpr(MCExpr::Binary, Loc), Op(Op), LHS(LHS), RHS(RHS) {}
 
 public:
   /// \name Construction
   /// @{
 
   static const MCBinaryExpr *create(Opcode Op, const MCExpr *LHS,
-                                    const MCExpr *RHS, MCContext &Ctx);
+                                    const MCExpr *RHS, MCContext &Ctx,
+                                    SMLoc Loc = SMLoc());
   static const MCBinaryExpr *createAdd(const MCExpr *LHS, const MCExpr *RHS,
                                        MCContext &Ctx) {
     return create(Add, LHS, RHS, Ctx);
@@ -531,7 +536,7 @@
 class MCTargetExpr : public MCExpr {
   virtual void anchor();
 protected:
-  MCTargetExpr() : MCExpr(Target) {}
+  MCTargetExpr() : MCExpr(Target, SMLoc()) {}
   virtual ~MCTargetExpr() {}
 public:
   virtual void printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const = 0;
Index: llvm/trunk/lib/MC/MCExpr.cpp
===================================================================
--- llvm/trunk/lib/MC/MCExpr.cpp
+++ llvm/trunk/lib/MC/MCExpr.cpp
@@ -137,8 +137,9 @@
 /* *** */
 
 const MCBinaryExpr *MCBinaryExpr::create(Opcode Opc, const MCExpr *LHS,
-                                         const MCExpr *RHS, MCContext &Ctx) {
-  return new (Ctx) MCBinaryExpr(Opc, LHS, RHS);
+                                         const MCExpr *RHS, MCContext &Ctx,
+                                         SMLoc Loc) {
+  return new (Ctx) MCBinaryExpr(Opc, LHS, RHS, Loc);
 }
 
 const MCUnaryExpr *MCUnaryExpr::create(Opcode Opc, const MCExpr *Expr,
@@ -153,8 +154,8 @@
 /* *** */
 
 MCSymbolRefExpr::MCSymbolRefExpr(const MCSymbol *Symbol, VariantKind Kind,
-                                 const MCAsmInfo *MAI)
-    : MCExpr(MCExpr::SymbolRef), Kind(Kind),
+                                 const MCAsmInfo *MAI, SMLoc Loc)
+    : MCExpr(MCExpr::SymbolRef, Loc), Kind(Kind),
       UseParensForSymbolVariant(MAI->useParensForSymbolVariant()),
       HasSubsectionsViaSymbols(MAI->hasSubsectionsViaSymbols()),
       Symbol(Symbol) {
@@ -163,8 +164,8 @@
 
 const MCSymbolRefExpr *MCSymbolRefExpr::create(const MCSymbol *Sym,
                                                VariantKind Kind,
-                                               MCContext &Ctx) {
-  return new (Ctx) MCSymbolRefExpr(Sym, Kind, Ctx.getAsmInfo());
+                                               MCContext &Ctx, SMLoc Loc) {
+  return new (Ctx) MCSymbolRefExpr(Sym, Kind, Ctx.getAsmInfo(), Loc);
 }
 
 const MCSymbolRefExpr *MCSymbolRefExpr::create(StringRef Name, VariantKind Kind,
Index: llvm/trunk/lib/MC/MCFragment.cpp
===================================================================
--- llvm/trunk/lib/MC/MCFragment.cpp
+++ llvm/trunk/lib/MC/MCFragment.cpp
@@ -145,14 +145,14 @@
   MCValue Value;
   if (!Expr->evaluateAsValue(Value, *this)) {
     Assembler.getContext().reportError(
-        SMLoc(), "expression could not be evaluated");
+        Expr->getLoc(), "expression could not be evaluated");
     return nullptr;
   }
 
   const MCSymbolRefExpr *RefB = Value.getSymB();
   if (RefB) {
     Assembler.getContext().reportError(
-        SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
+        Expr->getLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
                      "' could not be evaluated in a subtraction expression");
     return nullptr;
   }
@@ -164,8 +164,7 @@
   const MCSymbol &ASym = A->getSymbol();
   const MCAssembler &Asm = getAssembler();
   if (ASym.isCommon()) {
-    // FIXME: we should probably add a SMLoc to MCExpr.
-    Asm.getContext().reportError(SMLoc(),
+    Asm.getContext().reportError(Expr->getLoc(),
                                  "Common symbol '" + ASym.getName() +
                                      "' cannot be used in assignment expr");
     return nullptr;
Index: llvm/trunk/lib/MC/MCParser/AsmParser.cpp
===================================================================
--- llvm/trunk/lib/MC/MCParser/AsmParser.cpp
+++ llvm/trunk/lib/MC/MCParser/AsmParser.cpp
@@ -1005,7 +1005,7 @@
     }
 
     // Otherwise create a symbol ref.
-    Res = MCSymbolRefExpr::create(Sym, Variant, getContext());
+    Res = MCSymbolRefExpr::create(Sym, Variant, getContext(), FirstTokenLoc);
     return false;
   }
   case AsmToken::BigNum:
@@ -1436,6 +1436,7 @@
 /// Res contains the LHS of the expression on input.
 bool AsmParser::parseBinOpRHS(unsigned Precedence, const MCExpr *&Res,
                               SMLoc &EndLoc) {
+  SMLoc StartLoc = Lexer.getLoc();
   while (true) {
     MCBinaryExpr::Opcode Kind = MCBinaryExpr::Add;
     unsigned TokPrec = getBinOpPrecedence(Lexer.getKind(), Kind);
@@ -1460,7 +1461,7 @@
       return true;
 
     // Merge LHS and RHS according to operator.
-    Res = MCBinaryExpr::create(Kind, Res, RHS, getContext());
+    Res = MCBinaryExpr::create(Kind, Res, RHS, getContext(), StartLoc);
   }
 }
 
Index: llvm/trunk/test/MC/AArch64/error-location-post-layout.s
===================================================================
--- llvm/trunk/test/MC/AArch64/error-location-post-layout.s
+++ llvm/trunk/test/MC/AArch64/error-location-post-layout.s
@@ -1,14 +1,11 @@
 // RUN: not llvm-mc -triple aarch64--none-eabi -filetype obj < %s -o /dev/null 2>&1 | FileCheck %s
 
-// Note: These errors are not always emitted in the order in which the relevant
-// source appears, this file is carefully ordered so that that is the case.
-
-// CHECK: <unknown>:0: error: expression could not be evaluated
   .set v1, -undef
+// CHECK: <unknown>:0: error: expression could not be evaluated
 
   .comm common, 4
-// CHECK: <unknown>:0: error: Common symbol 'common' cannot be used in assignment expr
   .set v3, common
+// CHECK: 7:12: error: Common symbol 'common' cannot be used in assignment expr
 
-// CHECK: <unknown>:0: error: symbol 'undef' could not be evaluated in a subtraction expression
   .set v2, a-undef
+// CHECK: 10:13: error: symbol 'undef' could not be evaluated in a subtraction expression
Index: llvm/trunk/test/MC/ARM/error-location-post-layout.s
===================================================================
--- llvm/trunk/test/MC/ARM/error-location-post-layout.s
+++ llvm/trunk/test/MC/ARM/error-location-post-layout.s
@@ -1,14 +1,14 @@
 @ RUN: not llvm-mc -triple armv7a--none-eabi -filetype obj < %s -o /dev/null 2>&1 | FileCheck %s
 
-@ Note: These errors are not always emitted in the order in which the relevant
-@ source appears, this file is carefully ordered so that that is the case.
-
-@ CHECK: <unknown>:0: error: expression could not be evaluated
   .set v1, -undef
+@ CHECK: <unknown>:0: error: expression could not be evaluated
 
   .comm common, 4
-@ CHECK: <unknown>:0: error: Common symbol 'common' cannot be used in assignment expr
   .set v3, common
+@ CHECK: 7:12: error: Common symbol 'common' cannot be used in assignment expr
 
-@ CHECK: <unknown>:0: error: symbol 'undef' could not be evaluated in a subtraction expression
   .set v2, a-undef
+@ CHECK-DAG: 10:13: error: symbol 'undef' could not be evaluated in a subtraction expression
+
+  .equ STACK_START, (a + undef)
+@ CHECK-DAG: 13:24: error: expression could not be evaluated