[sil-combine] Minor improvement to the peephole for removal of alloc_ref instructions that are only allocated and then deallocated

Author: swiftix

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -447,7 +447,8 @@ SILInstruction *SILCombiner::visitAllocRefInst(AllocRefInst *AR) {
     auto *Op = *UI;
     ++UI;
     auto *User = Op->getUser();
-    if (!isa<DeallocRefInst>(User) && !isa<SetDeallocatingInst>(User)) {
+    if (!isa<DeallocRefInst>(User) && !isa<SetDeallocatingInst>(User) &&
+        !isa<FixLifetimeInst>(User)) {
       HasNonRemovableUses = true;
       break;
     }

test/SILOptimizer/sil_combine.sil

@@ -2413,6 +2413,20 @@ bb0(%0 : $*B):
   return %2 : $()
 }
 
+// CHECK-LABEL: sil @delete_dead_alloc_ref
+// CHECK: bb0
+// CHECK-NEXT: tuple
+// CHECK-NEXT: return
+sil @delete_dead_alloc_ref : $() -> () {
+bb0:
+  %1 = alloc_ref $B
+  set_deallocating %1 : $B
+  fix_lifetime %1 : $B
+  dealloc_ref %1 : $B
+  %2 = tuple()
+  return %2 : $()
+}
+
 // CHECK-LABEL: sil @delete_dead_alloc_stack2
 // CHECK: bb0
 // CHECK-NEXT: destroy_addr %0