Support target Assemblers without a zero directive

[borisboesler]

Summary

MCAsmStreamer fails to emit fill bytes if the target's assembler does not provide a zero directive to fill a number of bytes in memory with a given value. If the directive does not exist an empty MCStreamer::emitFill() is called. A nested code block does emit bytes with a Data8BitsDirective, but is inside a if (const char *ZeroDirective = MAI->getZeroDirective()) block. This should be the fall through case.

[daltenty]

Thanks for fixing this. Can you provide a test case for one of the targets which doesn't initialize ZeroDirective?

[borisboesler]

In D114874#3166973, @daltenty wrote:

Thanks for fixing this. Can you provide a test case for one of the targets which doesn't initialize ZeroDirective?

All targets support a ZeroDirective; its initial value is "\t.zero\t" and some targets overwrite it with "\t.space\t"or "\t.skip\t" or ".b8". My out of source target does not support such a directive.

What would the result of the target tests be, if I set ZeroDirective = nullptr; in each target? Do the test expect a .zero or similar?

llvm/lib/MC/MCAsmStreamer.cpp

void MCAsmStreamer::emitFill(const MCExpr &NumBytes, uint64_t FillValue,
   if (const char *ZeroDirective = MAI->getZeroDirective()) {
     if (MAI->doesZeroDirectiveSupportNonZeroValue() || FillValue == 0) {
       // FIXME: Emit location directives
       OS << ZeroDirective;
       NumBytes.print(OS, MAI);
       if (FillValue != 0)
         OS << ',' << (int)FillValue;
       EmitEOL();
-    } else {
-      if (!IsAbsolute)
-        report_fatal_error(
-            "Cannot emit non-absolute expression lengths of fill.");
-      for (int i = 0; i < IntNumBytes; ++i) {
-        OS << MAI->getData8bitsDirective() << (int)FillValue;
-        EmitEOL();
-      }
-    }
-    return;
-  }
-
-  MCStreamer::emitFill(NumBytes, FillValue);
-}
+      return;
+    }
+  }
+
+    report_fatal_error("Cannot emit non-absolute expression lengths of fill.");
 
 void MCAsmStreamer::emitFill(const MCExpr &NumValues, int64_t Size,
                              int64_t Expr, SMLoc Loc) {
   // FIXME: Emit location directives
   OS << "\t.fill\t";
   NumValues.print(OS, MAI);
   OS << ", " << Size << ", 0x";
   OS.write_hex(truncateToSize(Expr, 4));