JIT: Skip moving BBJ_COND jump target if fallthrough target is equally likely (#105084)

amanasifkhalid · web-flow · commit c70791346cb7 · 2024-07-18T17:51:04.000-04:00
diff --git a/src/coreclr/jit/fgopt.cpp b/src/coreclr/jit/fgopt.cpp
@@ -4536,6 +4536,13 @@ void Compiler::fgMoveHotJumps()
                 targetEdge   = block->GetFalseEdge();
                 unlikelyEdge = block->GetTrueEdge();
             }
+
+            // If we aren't sure which successor is hotter, and we already fall into one of them,
+            // do nothing
+            if ((unlikelyEdge->getLikelihood() == 0.5) && block->NextIs(unlikelyEdge->getDestinationBlock()))
+            {
+                continue;
+            }
         }
         else
         {

Original file line number	Diff line number	Diff line change
`@@ -4536,6 +4536,13 @@ void Compiler::fgMoveHotJumps()`
`4536`	`4536`	`targetEdge = block->GetFalseEdge();`
`4537`	`4537`	`unlikelyEdge = block->GetTrueEdge();`
`4538`	`4538`	`}`
	`4539`	`+`
	`4540`	`+ // If we aren't sure which successor is hotter, and we already fall into one of them,`
	`4541`	`+ // do nothing`
	`4542`	`+ if ((unlikelyEdge->getLikelihood() == 0.5) && block->NextIs(unlikelyEdge->getDestinationBlock()))`
	`4543`	`+ {`
	`4544`	`+ continue;`
	`4545`	`+ }`
`4539`	`4546`	`}`
`4540`	`4547`	`else`
`4541`	`4548`	`{`