Do not emit shadow copied for inout parameters (#5218)

radar rdar://problem/28434323

SILGen has no reason to insert shadow copies for inout parameters any more. They cannot be captured. We still emit these copies. Sometimes deshadowing removes them, but sometimes it does not.

In this PR we just avoid emitting the copies and remove the deshadowing pass.

This PR chery-picked some of @dduan work and built on top of it.

Author: Joe Shajrawi

include/swift/SILOptimizer/PassManager/Passes.def

@@ -133,8 +133,6 @@ PASS(HighLevelLICM, "high-level-licm",
      "High Level Loop invariant code motion")
 PASS(IVInfoPrinter, "iv-info-printer",
      "Display induction variable information")
-PASS(InOutDeshadowing, "inout-deshadow",
-     "Remove inout argument shadow variables")
 PASS(InstCount, "inst-count",
      "Count all instructions in the module using llvm Statistics")
 PASS(JumpThreadSimplifyCFG, "simplify-cfg",

lib/SIL/TypeLowering.cpp

@@ -121,6 +121,10 @@ CaptureKind TypeConverter::getDeclCaptureKind(CapturedValue capture) {
       if (var->isLet() && !getTypeLowering(var->getType()).isAddressOnly())
         return CaptureKind::Constant;
 
+      if (var->getType()->is<InOutType>()) {
+        return CaptureKind::StorageAddress;
+      }
+
       // If we're capturing into a non-escaping closure, we can generally just
       // capture the address of the value as no-escape.
       return capture.isNoEscape() ?

lib/SILGen/SILGenProlog.cpp

@@ -262,30 +262,18 @@ struct ArgumentInitHelper {
         gen.B.createDebugValueAddr(loc, address, {vd->isLet(), ArgNo});
         return;
       }
-
-      // Allocate the local variable for the inout.
-      auto initVar = gen.emitLocalVariableWithCleanup(vd, false, ArgNo);
-
-      // Initialize with the value from the inout with an "autogenerated"
-      // copyaddr.
-      loc.markAutoGenerated();
-      gen.B.createCopyAddr(loc, address, initVar->getAddress(),
-                           IsNotTake, IsInitialization);
-      initVar->finishInitialization(gen);
-
-      // Set up a cleanup to write back to the inout.
-      gen.Cleanups.pushCleanup<CleanupWriteBackToInOut>(vd, address);
+      assert(argrv.getType().isAddress() && "expected inout to be address");
     } else {
       assert(vd->isLet() && "expected parameter to be immutable!");
       // If the variable is immutable, we can bind the value as is.
       // Leave the cleanup on the argument, if any, in place to consume the
       // argument if we're responsible for it.
-      gen.VarLocs[vd] = SILGenFunction::VarLoc::get(argrv.getValue());
-      if (argrv.getType().isAddress())
-        gen.B.createDebugValueAddr(loc, argrv.getValue(), {vd->isLet(), ArgNo});
-      else
-        gen.B.createDebugValue(loc, argrv.getValue(), {vd->isLet(), ArgNo});
     }
+    gen.VarLocs[vd] = SILGenFunction::VarLoc::get(argrv.getValue());
+    if (argrv.getType().isAddress())
+      gen.B.createDebugValueAddr(loc, argrv.getValue(), {vd->isLet(), ArgNo});
+    else
+      gen.B.createDebugValue(loc, argrv.getValue(), {vd->isLet(), ArgNo});
   }
 
   void emitParam(ParamDecl *PD) {

lib/SILOptimizer/Mandatory/CMakeLists.txt

@@ -6,5 +6,4 @@ set(MANDATORY_SOURCES
   Mandatory/DiagnoseUnreachable.cpp
   Mandatory/PredictableMemOpt.cpp
   Mandatory/ConstantPropagation.cpp
-  Mandatory/InOutDeshadowing.cpp
   PARENT_SCOPE)

lib/SILOptimizer/Mandatory/InOutDeshadowing.cpp

@@ -89,7 +89,6 @@ bool swift::runSILDiagnosticPasses(SILModule &Module) {
   // Otherwise run the rest of diagnostics.
   PM.addCapturePromotion();
   PM.addAllocBoxToStack();
-  PM.addInOutDeshadowing();
   PM.addNoReturnFolding();
   PM.addDefiniteInitialization();