Filter blocks to be used for hiding alignment instruction (#62262)

* fix for #61899

* proper fix

* Fix for #62238

* misc change

* Revert "fix for #61899"

This reverts commit 1fc26a5.

* fix formatting

* fix formatting once again

* add validJumpKind check

* review comments

Author: kunalspathak

src/coreclr/jit/compiler.cpp

@@ -5245,26 +5245,42 @@ void Compiler::placeLoopAlignInstructions()
     JITDUMP("Inside placeLoopAlignInstructions for %d loops.\n", loopAlignCandidates);
 
     // Add align only if there were any loops that needed alignment
-    weight_t    minBlockSoFar = BB_MAX_WEIGHT;
-    BasicBlock* bbHavingAlign = nullptr;
+    weight_t               minBlockSoFar         = BB_MAX_WEIGHT;
+    BasicBlock*            bbHavingAlign         = nullptr;
+    BasicBlock::loopNumber currentAlignedLoopNum = BasicBlock::NOT_IN_LOOP;
+
+    if ((fgFirstBB != nullptr) && fgFirstBB->isLoopAlign())
+    {
+        // Adding align instruction in prolog is not supported
+        // hence just remove that loop from our list.
+        loopsToProcess--;
+    }
+
     for (BasicBlock* const block : Blocks())
     {
-        if ((block == fgFirstBB) && block->isLoopAlign())
+        if (currentAlignedLoopNum != BasicBlock::NOT_IN_LOOP)
         {
-            // Adding align instruction in prolog is not supported
-            // hence skip the align block if it is the first block.
-            loopsToProcess--;
-            continue;
+            // We've been processing blocks within an aligned loop. Are we out of that loop now?
+            if (currentAlignedLoopNum != block->bbNatLoopNum)
+            {
+                currentAlignedLoopNum = BasicBlock::NOT_IN_LOOP;
+            }
         }
 
-        // If there is a unconditional jump
-        if (opts.compJitHideAlignBehindJmp && (block->bbJumpKind == BBJ_ALWAYS))
+        // If there is a unconditional jump (which is not part of callf/always pair)
+        if (opts.compJitHideAlignBehindJmp && (block->bbJumpKind == BBJ_ALWAYS) && !block->isBBCallAlwaysPairTail())
         {
+            // Track the lower weight blocks
             if (block->bbWeight < minBlockSoFar)
             {
-                minBlockSoFar = block->bbWeight;
-                bbHavingAlign = block;
-                JITDUMP(FMT_BB ", bbWeight=" FMT_WT " ends with unconditional 'jmp' \n", block->bbNum, block->bbWeight);
+                if (currentAlignedLoopNum == BasicBlock::NOT_IN_LOOP)
+                {
+                    // Ok to insert align instruction in this block because it is not part of any aligned loop.
+                    minBlockSoFar = block->bbWeight;
+                    bbHavingAlign = block;
+                    JITDUMP(FMT_BB ", bbWeight=" FMT_WT " ends with unconditional 'jmp' \n", block->bbNum,
+                            block->bbWeight);
+                }
             }
         }
 
@@ -5285,8 +5301,9 @@ void Compiler::placeLoopAlignInstructions()
             }
 
             bbHavingAlign->bbFlags |= BBF_HAS_ALIGN;
-            minBlockSoFar = BB_MAX_WEIGHT;
-            bbHavingAlign = nullptr;
+            minBlockSoFar         = BB_MAX_WEIGHT;
+            bbHavingAlign         = nullptr;
+            currentAlignedLoopNum = block->bbNext->bbNatLoopNum;
 
             if (--loopsToProcess == 0)
             {