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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191368 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 28 insertions, 3 deletions

diff --git a/include/llvm/MC/MCAsmInfo.h b/include/llvm/MC/MCAsmInfo.h
index f5acd17..3734d7e 100644
--- a/include/llvm/MC/MCAsmInfo.h
+++ b/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 '$' token, when not referencing an identifier or
+    /// constant, refers to the current PC.
+    bool DollarIsPC;                         // Defaults to false.
+
     /// SeparatorString - This string, if specified, is used to separate
     /// instructions from each other when on the same line.
     const char *SeparatorString;             // Defaults to ';'
@@ -421,6 +425,9 @@ namespace llvm {
     unsigned getMinInstAlignment() const {
       return MinInstAlignment;
     }
+    bool getDollarIsPC() const {
+      return DollarIsPC;
+    }
     const char *getSeparatorString() const {
       return SeparatorString;
     }
diff --git a/lib/MC/MCAsmInfo.cpp b/lib/MC/MCAsmInfo.cpp
index 73dc74a..152aae1 100644
--- a/lib/MC/MCAsmInfo.cpp
+++ b/lib/MC/MCAsmInfo.cpp
@@ -35,6 +35,7 @@ MCAsmInfo::MCAsmInfo() {
   LinkerRequiresNonEmptyDwarfLines = false;
   MaxInstLength = 4;
   MinInstAlignment = 1;
+  DollarIsPC = false;
   SeparatorString = ";";
   CommentColumn = 40;
   CommentString = "#";
diff --git a/lib/MC/MCParser/AsmParser.cpp b/lib/MC/MCParser/AsmParser.cpp
index 1267dc8..21cbd34 100644
--- a/lib/MC/MCParser/AsmParser.cpp
+++ b/lib/MC/MCParser/AsmParser.cpp
@@ -772,9 +772,19 @@ bool AsmParser::parsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc) {
   case AsmToken::Identifier: {
     StringRef Identifier;
     if (parseIdentifier(Identifier)) {
-      if (FirstTokenKind == AsmToken::Dollar)
-        return Error(FirstTokenLoc, "invalid token in expression");
-      return true;
+      if (FirstTokenKind == AsmToken::Dollar) {
+        if (Lexer.getMAI().getDollarIsPC()) {
+          // This is a '$' 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/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp b/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
index 1f3e5b4..91578a9 100644
--- a/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp
+++ b/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/test/MC/PowerPC/ppc64-operands.s b/test/MC/PowerPC/ppc64-operands.s
index cb96fd4..fc1cbeb 100644
--- a/test/MC/PowerPC/ppc64-operands.s
+++ b/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