[PATCH] D20337: [MC] Support symbolic expressions in assembly directives

[Rafael Espíndola via llvm-commits]

What happens if you try to print the assembly back out? I.e., if you run
llvm-mc with filetype=obj?

Cheers,
Rafael
On May 17, 2016 5:48 PM, "Petr Hosek via llvm-commits" <
llvm-commits at lists.llvm.org> wrote:

phosek created this revision.
phosek added a subscriber: llvm-commits.
phosek set the repository for this revision to rL LLVM.

This matches the behavior of GNU assembler which supports symbolic
expressions in absolute expressions used in assembly directives.

Repository:
  rL LLVM

http://reviews.llvm.org/D20337

Files:
  include/llvm/MC/MCObjectStreamer.h
  include/llvm/MC/MCStreamer.h
  lib/MC/MCParser/AsmParser.cpp
  test/MC/AsmParser/symbolic-expression.s

Index: test/MC/AsmParser/symbolic-expression.s
===================================================================
--- /dev/null
+++ test/MC/AsmParser/symbolic-expression.s
@@ -0,0 +1,18 @@
+# RUN: llvm-mc -filetype=obj -triple=i386-unknown-elf %s | llvm-objdump -t
- | FileCheck %s
+
+# CHECK: 00000000         .text           00000000 TEST0
+TEST0:
+  .fill 0x10
+# CHECK: 00000010         .text           00000000 TEST1
+TEST1:
+  .fill TEST1 - TEST0 + 0x5
+# CHECK: 00000025         .text           00000000 TEST2
+TEST2:
+  .zero TEST2 - (TEST1 + 0x5)
+# CHECK: 00000035         .text           00000000 TEST3
+TEST3:
+  .align (TEST1 - TEST0) * 8
+# CHECK: 00000080         .text           00000000 TEST4
+TEST4:
+# CHECK: 00000015 g       *COM*           00000010 a
+  .comm a, TEST2 - TEST1, TEST1 - TEST0
Index: lib/MC/MCParser/AsmParser.cpp
===================================================================
--- lib/MC/MCParser/AsmParser.cpp
+++ lib/MC/MCParser/AsmParser.cpp
@@ -1131,7 +1131,7 @@
   if (parseExpression(Expr))
     return true;

-  if (!Expr->evaluateAsAbsolute(Res))
+  if (!getStreamer().evaluateAsAbsolute(Expr, Res))
     return Error(StartLoc, "expected absolute expression");

   return false;
Index: include/llvm/MC/MCStreamer.h
===================================================================
--- include/llvm/MC/MCStreamer.h
+++ include/llvm/MC/MCStreamer.h
@@ -772,6 +772,11 @@
   void Finish();

   virtual bool mayHaveInstructions(MCSection &Sec) const { return true; }
+
+  /// \brief Try to evaluate the \p Value as an absolute value.
+  virtual bool evaluateAsAbsolute(const MCExpr *Value, int64_t &Res) {
+    return Value->evaluateAsAbsolute(Res);
+  }
 };

 /// Create a dummy machine code streamer, which does nothing. This is
useful for
Index: include/llvm/MC/MCObjectStreamer.h
===================================================================
--- include/llvm/MC/MCObjectStreamer.h
+++ include/llvm/MC/MCObjectStreamer.h
@@ -154,6 +154,12 @@
                               unsigned Size) override;

   bool mayHaveInstructions(MCSection &Sec) const override;
+
+  bool evaluateAsAbsolute(const MCExpr *Value, int64_t &Res) override {
+    MCDataFragment *DF = getOrCreateDataFragment();
+    flushPendingLabels(DF, DF->getContents().size());
+    return Value->evaluateAsAbsolute(Res, getAssembler());
+  }
 };

 } // end namespace llvm



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