[PATCH] [lld] [LinkerScript] Implement linker script expression evaluation

[Rui Ueyama]

================
Comment at: lib/ReaderWriter/LinkerScript.cpp:545
@@ +544,3 @@
+    return LinkerScriptReaderError::unknown_symbol_in_expr;
+  return symbolTable[_name];
+}
----------------
Maybe you want to use find and compare the return value with end, so that you don't look up the table twice.

================
Comment at: lib/ReaderWriter/LinkerScript.cpp:582
@@ +581,3 @@
+  case Unary::Minus:
+    return 0 - childRes;
+  case Unary::Not:
----------------
nit: return -childRes;

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Comment at: lib/ReaderWriter/LinkerScript.cpp:588
@@ +587,3 @@
+  llvm_unreachable("");
+  return 0;
+}
----------------
Remove this line. I believe llvm_unreachable has __attribute__((noreturn)), so no warning would be issued.

================
Comment at: lib/ReaderWriter/LinkerScript.cpp:674
@@ +673,3 @@
+  llvm_unreachable("");
+  return 0;
+}
----------------
Ditto

================
Comment at: lib/ReaderWriter/LinkerScript.cpp:705
@@ +704,3 @@
+    return falseExprRes;
+}
+
----------------
Is it okay to compute both "then" and "else" clauses regardless of a condition value? In a normal programming language, we don't do that -- for example, if (true) {} else { 1 / 0; } doesn't fail.

http://reviews.llvm.org/D8156

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