[PowerPC] Implement writeNopData

This implements a proper PPCAsmBackend::writeNopData routine
that actually writes PowerPC nop instructions.

This fixes the last remaining difference in object file output
(text section) between the integrated assembler and GNU as
that I've seen anywhere.

llvm-svn: 185662

llvm/lib/Target/PowerPC/MCTargetDesc/PPCAsmBackend.cpp

@@ -148,10 +148,14 @@ public:
   }
 
   bool writeNopData(uint64_t Count, MCObjectWriter *OW) const {
-    // FIXME: Zero fill for now. That's not right, but at least will get the
-    // section size right.
-    for (uint64_t i = 0; i != Count; ++i)
-      OW->Write8(0);
+    // Can't emit NOP with size not multiple of 32-bits
+    if (Count % 4 != 0)
+      return false;
+
+    uint64_t NumNops = Count / 4;
+    for (uint64_t i = 0; i != NumNops; ++i)
+      OW->Write32(0x60000000);
+
     return true;
   }
 

llvm/test/MC/PowerPC/ppc-nop.s

@@ -0,0 +1,9 @@
+# RUN: llvm-mc -filetype=obj -triple=powerpc-unknown-linux-gnu %s | llvm-readobj -s -sd - | FileCheck %s
+# RUN: llvm-mc -filetype=obj -triple=powerpc64-unknown-linux-gnu %s | llvm-readobj -s -sd - | FileCheck %s
+
+blr
+.p2align 3
+blr
+
+# CHECK:  0000: 4E800020 60000000 4E800020
+