[MC] Change AsmParser to leverage Assembler during evaluation

Teach AsmParser to check with Assembler for when evaluating constant
expressions.  This improves the handing of preprocessor expressions
that must be resolved at parse time. This idiom can be found as
assembling-time assertion checks in source-level assemblers. Note that
this relies on the MCStreamer to keep sufficient tabs on Section /
Fragment information which the MCAsmStreamer does not. As a result the
textual output may fail where the equivalent object generation would
pass. This can most easily be resolved by folding the MCAsmStreamer
and MCObjectStreamer together which is planned for in a separate
patch.

Currently, this feature is only enabled for assembly input, keeping IR
compilation consistent between assembly and object generation.

Reviewers: echristo, rnk, probinson, espindola, peter.smith

Reviewed By: peter.smith

Subscribers: eraman, peter.smith, arichardson, jyknight, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D45164

llvm-svn: 331218

1 files changed, 10 insertions, 7 deletions

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 7ee8e1b3e84..c2410413a62 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -775,7 +775,7 @@ bool AsmParser::processIncbinFile(const std::string &Filename, int64_t Skip,
   Bytes = Bytes.drop_front(Skip);
   if (Count) {
     int64_t Res;
-    if (!Count->evaluateAsAbsolute(Res))
+    if (!Count->evaluateAsAbsolute(Res, getStreamer().getAssemblerPtr()))
       return Error(Loc, "expected absolute expression");
     if (Res < 0)
       return Warning(Loc, "negative count has no effect");
@@ -1378,7 +1378,8 @@ bool AsmParser::parseExpression(const MCExpr *&Res, SMLoc &EndLoc) {
     Lex();
   }
 
-  // Try to constant fold it up front, if possible.
+  // Try to constant fold it up front, if possible. Do not exploit
+  // assembler here.
   int64_t Value;
   if (Res->evaluateAsAbsolute(Value))
     Res = MCConstantExpr::create(Value, getContext());
@@ -1419,7 +1420,7 @@ bool AsmParser::parseAbsoluteExpression(int64_t &Res) {
   if (parseExpression(Expr))
     return true;
 
-  if (!Expr->evaluateAsAbsolute(Res))
+  if (!Expr->evaluateAsAbsolute(Res, getStreamer().getAssemblerPtr()))
     return Error(StartLoc, "expected absolute expression");
 
   return false;
@@ -2616,7 +2617,8 @@ bool AsmParser::parseMacroArguments(const MCAsmMacro *M,
         Lex();
         if (parseExpression(AbsoluteExp, EndLoc))
           return false;
-        if (!AbsoluteExp->evaluateAsAbsolute(Value))
+        if (!AbsoluteExp->evaluateAsAbsolute(Value,
+                                             getStreamer().getAssemblerPtr()))
           return Error(StrLoc, "expected absolute expression");
         const char *StrChar = StrLoc.getPointer();
         const char *EndChar = EndLoc.getPointer();
@@ -2916,8 +2918,9 @@ bool AsmParser::parseDirectiveReloc(SMLoc DirectiveLoc) {
   if (parseExpression(Offset))
     return true;
 
-  if (check(!Offset->evaluateAsAbsolute(OffsetValue), OffsetLoc,
-            "expression is not a constant value") ||
+  if (check(!Offset->evaluateAsAbsolute(OffsetValue,
+                                        getStreamer().getAssemblerPtr()),
+            OffsetLoc, "expression is not a constant value") ||
       check(OffsetValue < 0, OffsetLoc, "expression is negative") ||
       parseToken(AsmToken::Comma, "expected comma") ||
       check(getTok().isNot(AsmToken::Identifier), "expected relocation name"))
@@ -5344,7 +5347,7 @@ bool AsmParser::parseDirectiveRept(SMLoc DirectiveLoc, StringRef Dir) {
     return true;
 
   int64_t Count;
-  if (!CountExpr->evaluateAsAbsolute(Count)) {
+  if (!CountExpr->evaluateAsAbsolute(Count, getStreamer().getAssemblerPtr())) {
     return Error(CountLoc, "unexpected token in '" + Dir + "' directive");
   }