Loop alignment: Fix loop size calculation to exclude IG's size that are marked as not aligned

src/coreclr/jit/emit.cpp

@@ -5096,10 +5096,14 @@ unsigned emitter::getLoopSize(insGroup* igLoopHeader, unsigned maxLoopSize DEBUG
 {
  unsigned loopSize = 0;
 
+ JITDUMP("*************** In getLoopSize() for %s\n", emitLabelString(igLoopHeader), loopSize);
+
  for (insGroup* igInLoop = igLoopHeader; igInLoop != nullptr; igInLoop = igInLoop->igNext)
  {
  loopSize += igInLoop->igSize;
- if (igInLoop->endsWithAlignInstr())
+ JITDUMP(" %s has %u bytes.", emitLabelString(igInLoop), igInLoop->igSize);
+
+ if (igInLoop->endsWithAlignInstr() /*|| (igInLoop->igFlags & IGF_REMOVED_ALIGN)*/)
  {
  // If IGF_HAS_ALIGN is present, igInLoop contains align instruction at the end,
  // for next IG or some future IG.
@@ -5179,16 +5183,35 @@ unsigned emitter::getLoopSize(insGroup* igLoopHeader, unsigned maxLoopSize DEBUG
  else
 #endif
  {
+ JITDUMP(" but ends with align instruction, taking off %u bytes.",
+ emitComp->opts.compJitAlignPaddingLimit);
  // The current loop size should exclude the align instruction size reserved for next loop.
  loopSize -= emitComp->opts.compJitAlignPaddingLimit;
  }
  }
+ else if (igInLoop->igFlags & IGF_REMOVED_ALIGN)
+ {
+ assert("!Failed to remove 15 bytes");
+ }
  if ((igInLoop->igLoopBackEdge == igLoopHeader) || (loopSize > maxLoopSize))
  {
+#ifdef DEBUG
+ if (igInLoop->igLoopBackEdge == igLoopHeader)
+ {
+ JITDUMP(" -- Found the back edge.");
+ }
+ else
+ {
+ JITDUMP(" -- loopSize exceeded the threshold of %u bytes.", maxLoopSize);
+ }
+ JITDUMP("\n");
  break;
+#endif
  }
+ JITDUMP("\n");
  }
 
+ JITDUMP("loopSize of %s = %u bytes.\n", emitLabelString(igLoopHeader), loopSize);
  return loopSize;
 }
 
@@ -5280,9 +5303,10 @@ void emitter::emitSetLoopBackEdge(BasicBlock* loopTopBlock)
 
  // This IG should no longer contain alignment instruction
  alignInstr->removeAlignFlags();
+ alignInstr->idaIG->igFlags |= IGF_REMOVED_ALIGN;
 
  markedCurrLoop = true;
- JITDUMP("** Skip alignment for current loop IG%02u ~ IG%02u because it encloses an aligned loop "
+ JITDUMP(";; Skip alignment for current loop IG%02u ~ IG%02u because it encloses an aligned loop "
  "IG%02u ~ IG%02u.\n",
  currLoopStart, currLoopEnd, emitLastLoopStart, emitLastLoopEnd);
  }
@@ -5296,9 +5320,10 @@ void emitter::emitSetLoopBackEdge(BasicBlock* loopTopBlock)
 
  // This IG should no longer contain alignment instruction
  alignInstr->removeAlignFlags();
+ alignInstr->idaIG->igFlags |= IGF_REMOVED_ALIGN;
 
  markedLastLoop = true;
- JITDUMP("** Skip alignment for aligned loop IG%02u ~ IG%02u because it encloses the current loop "
+ JITDUMP(";; Skip alignment for aligned loop IG%02u ~ IG%02u because it encloses the current loop "
  "IG%02u ~ IG%02u.\n",
  emitLastLoopStart, emitLastLoopEnd, currLoopStart, currLoopEnd);
  }

src/coreclr/jit/emit.h

@@ -277,6 +277,8 @@ struct insGroup
  // and the emitter should continue to track GC info as if there was no new block.
 #define IGF_HAS_ALIGN 0x0400 // this group contains an alignment instruction(s) at the end to align either the next
  // IG, or, if this IG contains with an unconditional branch, some subsequent IG.
+#define IGF_REMOVED_ALIGN 0x0800 // this group had an alignment instruction(s) which was later removed without updating
+ // the IG's size/offsets.
 
 // Mask of IGF_* flags that should be propagated to new blocks when they are created.
 // This allows prologs and epilogs to be any number of IGs, but still be

src/coreclr/jit/optimizer.cpp

@@ -2625,7 +2625,7 @@ void Compiler::optIdentifyLoopsForAlignment()
  }
  else
  {
- JITDUMP("Skip alignment for " FMT_LP " that starts at " FMT_BB " weight=" FMT_WT ".\n", loopInd,
+ JITDUMP(";; Skip alignment for " FMT_LP " that starts at " FMT_BB " weight=" FMT_WT ".\n", loopInd,
  top->bbNum, topWeight);
  }
  }