ARM: improved assembler diagnostics for missing CPU features.

When an instruction match is found, but the subtarget features it
requires are not available (missing floating point unit, or thumb vs arm
mode, for example), issue a diagnostic that identifies what the feature
mismatch is.

rdar://11257547

llvm-svn: 155499

1 files changed, 16 insertions, 3 deletions

diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 2c53e3f8f8c..cbd9bdb77ca 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -7277,6 +7277,7 @@ unsigned ARMAsmParser::checkTargetMatchPredicate(MCInst &Inst) {
   return Match_Success;
 }
 
+static const char *getSubtargetFeatureName(unsigned Val);
 bool ARMAsmParser::
 MatchAndEmitInstruction(SMLoc IDLoc,
                         SmallVectorImpl<MCParsedAsmOperand*> &Operands,
@@ -7317,9 +7318,21 @@ MatchAndEmitInstruction(SMLoc IDLoc,
     Inst.setLoc(IDLoc);
     Out.EmitInstruction(Inst);
     return false;
-  case Match_MissingFeature:
-    Error(IDLoc, "instruction requires a CPU feature not currently enabled");
-    return true;
+  case Match_MissingFeature: {
+    assert(ErrorInfo && "Unknown missing feature!");
+    // Special case the error message for the very common case where only
+    // a single subtarget feature is missing (Thumb vs. ARM, e.g.).
+    std::string Msg = "instruction requires:";
+    unsigned Mask = 1;
+    for (unsigned i = 0; i < (sizeof(ErrorInfo)*8-1); ++i) {
+      if (ErrorInfo & Mask) {
+        Msg += " ";
+        Msg += getSubtargetFeatureName(ErrorInfo & Mask);
+      }
+      Mask <<= 1;
+    }
+    return Error(IDLoc, Msg);
+  }
   case Match_InvalidOperand: {
     SMLoc ErrorLoc = IDLoc;
     if (ErrorInfo != ~0U) {