From 0c58bc64a4bd40561ae044527c4e1f8190f435f7 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Wed, 25 Sep 2013 10:47:21 +0000
Subject: [PATCH] MC: Add support for treating $ as a reference to the PC

The binutils assembler supports a mode called DOLLAR_DOT which treats
the dollar sign token as a reference to the current program counter if
the dollar sign doesn't precede a constant or identifier.

This commit adds a new MCAsmInfo flag stating whether or not a given
target supports this interpretation of the dollar sign token; by
default, this flag is not enabled.

Further, enable this flag for PPC. The system assembler for AIX and
binutils both support using the dollar sign in this manner.

This fixes PR17353.

llvm-svn: 191368
---
 llvm/include/llvm/MC/MCAsmInfo.h                 |  7 +++++++
 llvm/lib/MC/MCAsmInfo.cpp                        |  1 +
 llvm/lib/MC/MCParser/AsmParser.cpp               | 16 +++++++++++++---
 .../Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp |  2 ++
 llvm/test/MC/PowerPC/ppc64-operands.s            |  5 +++++
 5 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/MC/MCAsmInfo.h b/llvm/include/llvm/MC/MCAsmInfo.h
index f5acd1716df4..3734d7e006b4 100644
--- a/llvm/include/llvm/MC/MCAsmInfo.h
+++ b/llvm/include/llvm/MC/MCAsmInfo.h
@@ -93,6 +93,10 @@ namespace llvm {
     /// this value.  Factored out in .debug_frame and .debug_line.
     unsigned MinInstAlignment;                  // Defaults to 1.
 
+    /// DollarIsPC - The '$' token, when not referencing an identifier or
+    /// constant, refers to the current PC.
+    bool DollarIsPC;                         // Defaults to false.
+
     /// SeparatorString - This string, if specified, is used to separate
     /// instructions from each other when on the same line.
     const char *SeparatorString;             // Defaults to ';'
@@ -421,6 +425,9 @@ namespace llvm {
     unsigned getMinInstAlignment() const {
       return MinInstAlignment;
     }
+    bool getDollarIsPC() const {
+      return DollarIsPC;
+    }
     const char *getSeparatorString() const {
       return SeparatorString;
     }
diff --git a/llvm/lib/MC/MCAsmInfo.cpp b/llvm/lib/MC/MCAsmInfo.cpp
index 73dc74a4f20d..152aae15af17 100644
--- a/llvm/lib/MC/MCAsmInfo.cpp
+++ b/llvm/lib/MC/MCAsmInfo.cpp
@@ -35,6 +35,7 @@ MCAsmInfo::MCAsmInfo() {
   LinkerRequiresNonEmptyDwarfLines = false;
   MaxInstLength = 4;
   MinInstAlignment = 1;
+  DollarIsPC = false;
   SeparatorString = ";";
   CommentColumn = 40;
   CommentString = "#";
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index 1267dc814cde..21cbd3416ca5 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -772,9 +772,19 @@ bool AsmParser::parsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc) {
   case AsmToken::Identifier: {
     StringRef Identifier;
     if (parseIdentifier(Identifier)) {
-      if (FirstTokenKind == AsmToken::Dollar)
-        return Error(FirstTokenLoc, "invalid token in expression");
-      return true;
+      if (FirstTokenKind == AsmToken::Dollar) {
+        if (Lexer.getMAI().getDollarIsPC()) {
+          // This is a '$' reference, which references the current PC.  Emit a
+          // temporary label to the streamer and refer to it.
+          MCSymbol *Sym = Ctx.CreateTempSymbol();
+          Out.EmitLabel(Sym);
+          Res = MCSymbolRefExpr::Create(Sym, MCSymbolRefExpr::VK_None, getContext());
+          EndLoc = FirstTokenLoc;
+          return false;
+        } else
+          return Error(FirstTokenLoc, "invalid token in expression");
+        return true;
+      }
     }
 
     EndLoc = SMLoc::getFromPointer(Identifier.end());
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
index 1f3e5b49a644..91578a9b5043 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
@@ -54,6 +54,8 @@ PPCLinuxMCAsmInfo::PPCLinuxMCAsmInfo(bool is64Bit) {
   // Debug Information
   SupportsDebugInformation = true;
 
+  DollarIsPC = true;
+
   // Set up DWARF directives
   HasLEB128 = true;  // Target asm supports leb128 directives (little-endian)
   MinInstAlignment = 4;
diff --git a/llvm/test/MC/PowerPC/ppc64-operands.s b/llvm/test/MC/PowerPC/ppc64-operands.s
index cb96fd458876..fc1cbeb94b94 100644
--- a/llvm/test/MC/PowerPC/ppc64-operands.s
+++ b/llvm/test/MC/PowerPC/ppc64-operands.s
@@ -108,3 +108,8 @@
 # CHECK: beqa 0, 1024                    # encoding: [0x41,0x82,0x04,0x02]
          beqa 1024
 
+# CHECK:                                 # encoding: [0x42,0x9f,A,0bAAAAAA01]
+         bcl 20, 31, $+4
+
+# CHECK:                                 # encoding: [0x42,0x00,A,0bAAAAAA00]
+         bdnz $-8