Fix symbol value computation when part of the expression is weak.

This matches the behaviour of the gnu assembler and is part of
fixing pr24486.

llvm-svn: 245576
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 4ec81b3..09a27fe 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -137,7 +137,7 @@
 
   // If SD is a variable, evaluate it.
   MCValue Target;
-  if (!S.getVariableValue()->evaluateAsRelocatable(Target, &Layout, nullptr))
+  if (!S.getVariableValue()->evaluateAsValue(Target, Layout))
     report_fatal_error("unable to evaluate offset for variable '" +
                        S.getName() + "'");
 
diff --git a/llvm/test/MC/X86/expand-var.s b/llvm/test/MC/X86/expand-var.s
index 8d5529a..d9b8bb9 100644
--- a/llvm/test/MC/X86/expand-var.s
+++ b/llvm/test/MC/X86/expand-var.s
@@ -1,9 +1,13 @@
-// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux < %s | llvm-readobj -r | FileCheck %s
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux < %s | llvm-readobj -r -t | FileCheck %s
 
 // CHECK:       Section {{.*}} .rela.text {
 // CHECK-NEXT:    0x0 R_X86_64_32 d 0x0
 // CHECK-NEXT:  }
 
+// CHECK:      Symbol {
+// CHECK:        Name:  d2
+// CHECK-NEXT:   Value: 0x2A
+
 a:
         b = a
         c = a
@@ -16,3 +20,4 @@
         .weak b2
         b2 = a2
         c2 = b2 - a2
+        d2 = b2 - a2 + 42