SimplifyCFG: Handle checked_cast_addr_br with consumption kind copy_on_success

We didn't optimize such casts with copy_on_success, which could result in very stupid code, e.g. for type identity casts (which should be a no-op).

Author: eeckstein

lib/SILOptimizer/Utils/CastOptimizer.cpp

@@ -918,25 +918,32 @@ SILInstruction *CastOptimizer::simplifyCheckedCastAddrBranchInst(
       return nullptr;
     }
 
-    // For CopyOnSuccess casts, we could insert an explicit copy here, but this
-    // case does not happen in practice.
-    //
     // Both TakeOnSuccess and TakeAlways can be reduced to an
     // UnconditionalCheckedCast, since the failure path is irrelevant.
+    AllocStackInst *copiedSrc = nullptr;
     switch (Inst->getConsumptionKind()) {
     case CastConsumptionKind::BorrowAlways:
       llvm_unreachable("checked_cast_addr_br never has BorrowAlways");
     case CastConsumptionKind::CopyOnSuccess:
-      return nullptr;
+      if (!Src->getType().isTrivial(*BB->getParent())) {
+        copiedSrc = Builder.createAllocStack(Loc, Src->getType());
+        Builder.createCopyAddr(Loc, Src, copiedSrc, IsNotTake, IsInitialization);
+        Src = copiedSrc;
+      }
+      break;
     case CastConsumptionKind::TakeAlways:
     case CastConsumptionKind::TakeOnSuccess:
       break;
     }
 
-    if (!emitSuccessfulIndirectUnconditionalCast(Builder, Loc, dynamicCast)) {
-      // No optimization was possible.
-      return nullptr;
-    }
+    bool result = emitSuccessfulIndirectUnconditionalCast(
+      Builder, Builder.getModule().getSwiftModule(), Loc, Src,
+      Inst->getSourceFormalType(), Dest, Inst->getTargetFormalType(), Inst);
+    (void)result;
+    assert(result && "emit cannot fail for an checked_cast_addr_br");
+
+    if (copiedSrc)
+      Builder.createDeallocStack(Loc, copiedSrc);
     eraseInstAction(Inst);
   }
   SILInstruction *NewI = &BB->back();

test/SILOptimizer/floating_point_conversion.swift

@@ -0,0 +1,25 @@
+// RUN: %target-swift-frontend -O -module-name=test -emit-sil %s | %FileCheck %s
+
+func convert<
+   T: BinaryFloatingPoint, U: BinaryFloatingPoint
+ >(_ value: T, to: U.Type) -> U {
+   U(value)
+}
+
+// Check that the follwing functions can be optimized to no-ops.
+
+// CHECK-LABEL: sil @$s4test0A6DoubleyS2dF
+// CHECK:   return %0
+// CHECK: } // end sil function '$s4test0A6DoubleyS2dF'
+public func testDouble(_ x: Double) -> Double {
+  return convert(x, to: Double.self)
+}
+
+// CHECK-LABEL: sil @$s4test0A5FloatyS2fF
+// CHECK:   return %0
+// CHECK: } // end sil function '$s4test0A5FloatyS2fF'
+public func testFloat(_ x: Float) -> Float {
+  return convert(x, to: Float.self)
+}
+
+

test/SILOptimizer/simplify_cfg.sil

@@ -2980,6 +2980,70 @@ bb3:
   br bb2(%z : $Builtin.Int1)
 }
 
+// CHECK-LABEL: sil @trivial_checked_cast_addr_br : $@convention(thin) (@guaranteed Int, @guaranteed Int) -> @owned Int
+// CHECK:   [[SRC:%.*]] = alloc_stack $Int
+// CHECK:   store %0 to [[SRC]]
+// CHECK:   [[DST:%.*]] = alloc_stack $Int
+// CHECK:   [[LD1:%.*]] = load [[SRC]]
+// CHECK:   store [[LD1]] to [[DST]]
+// CHECK:   [[LD2:%.*]] = load [[DST]]
+// CHECK:   return [[LD2]]
+// CHECK: } // end sil function 'trivial_checked_cast_addr_br'
+sil @trivial_checked_cast_addr_br : $@convention(thin) (@guaranteed Int, @guaranteed Int) -> @owned Int {
+bb0(%0 : $Int, %1 : $Int):
+  %6 = alloc_stack $Int
+  store %0 to %6 : $*Int
+  %8 = alloc_stack $Int
+  checked_cast_addr_br copy_on_success Int in %6 : $*Int to Int in %8 : $*Int, bb1, bb2
+
+bb1:
+  %10 = load %8 : $*Int
+  dealloc_stack %8 : $*Int
+  br bb3(%10 : $Int)
+
+bb2:
+  retain_value %1: $Int
+  dealloc_stack %8 : $*Int
+  br bb3(%1 : $Int)
+
+bb3(%11 : $Int):
+  dealloc_stack %6 : $*Int
+  return %11 : $Int
+}
+
+// CHECK-LABEL: sil @non_trivial_checked_cast_addr_br : $@convention(thin) (@guaranteed String, @guaranteed String) -> @owned String
+// CHECK:   [[SRC:%.*]] = alloc_stack $String
+// CHECK:   store %0 to [[SRC]]
+// CHECK:   [[DST:%.*]] = alloc_stack $String
+// CHECK:   [[TEMP:%.*]] = alloc_stack $String
+// CHECK:   copy_addr [[SRC]] to [initialization] [[TEMP]]
+// CHECK:   [[LD1:%.*]] = load [[TEMP]]
+// CHECK:   store [[LD1]] to [[DST]]
+// CHECK:   [[LD2:%.*]] = load [[DST]]
+// CHECK:   return [[LD2]]
+// CHECK: } // end sil function 'non_trivial_checked_cast_addr_br'
+sil @non_trivial_checked_cast_addr_br : $@convention(thin) (@guaranteed String, @guaranteed String) -> @owned String {
+bb0(%0 : $String, %1 : $String):
+  %6 = alloc_stack $String
+  store %0 to %6 : $*String
+  %8 = alloc_stack $String
+  checked_cast_addr_br copy_on_success String in %6 : $*String to String in %8 : $*String, bb1, bb2
+
+bb1:
+  %10 = load %8 : $*String
+  dealloc_stack %8 : $*String
+  br bb3(%10 : $String)
+
+bb2:
+  retain_value %1: $String
+  dealloc_stack %8 : $*String
+  br bb3(%1 : $String)
+
+bb3(%11 : $String):
+  dealloc_stack %6 : $*String
+  return %11 : $String
+}
+
 // CHECK-LABEL: sil @dont_hang
 // CHECK:      bb6:
 // CHECK:        integer_literal $Builtin.Int64, 1