Merge pull request swiftlang#19899 from eeckstein/fold-bridge-object-casts

Author: swift-ci

lib/SILOptimizer/SILCombiner/SILCombinerBuiltinVisitors.cpp

@@ -161,6 +161,18 @@ SILInstruction *SILCombiner::optimizeBuiltinZextOrBitCast(BuiltinInst *I) {
     replaceInstUsesWith(*I, NI);
     return eraseInstFromFunction(*I);
   }
+  // Optimize a sequence of conversion of an builtin integer to and from
+  // BridgeObject. This sequence appears in the String implementation.
+  if (auto *BO2W = dyn_cast<BridgeObjectToWordInst>(Op)) {
+    if (auto *V2BO = dyn_cast<ValueToBridgeObjectInst>(BO2W->getOperand())) {
+      if (auto *SI = dyn_cast<StructInst>(V2BO->getOperand())) {
+        if (SI->getNumOperands() == 1 && SI->getOperand(0)->getType() == I->getType()) {
+          replaceInstUsesWith(*I, SI->getOperand(0));
+          return eraseInstFromFunction(*I);
+        }
+      }
+    }
+  }
   return nullptr;
 }
 

test/SILOptimizer/sil_combine.sil

@@ -3637,3 +3637,15 @@ bb0:
   return %36 : $Builtin.Int64
 }
 
+// CHECK-LABEL: sil @conversion_to_and_from_bridge_object
+// CHECK:      bb0(%0 : $Builtin.Int64):
+// CHECK-NEXT:   return %0
+sil @conversion_to_and_from_bridge_object : $@convention(thin) (Builtin.Int64) -> (Builtin.Int64) {
+bb0(%0 : $Builtin.Int64):
+  %1 = struct $UInt64 (%0 : $Builtin.Int64)
+  %2 = value_to_bridge_object %1 : $UInt64
+  %3 = bridge_object_to_word %2 : $Builtin.BridgeObject to $Builtin.Word
+  %4 = builtin "zextOrBitCast_Word_Int64"(%3 : $Builtin.Word) : $Builtin.Int64
+  return %4 : $Builtin.Int64
+}
+