LargeTypesReg2Mem: Add a new heuristic that trys harder to keep large

values on the stack

This heuristic can be enabled by passing -Xfrontend
-enable-aggressive-reg2mem.

rdar://123916109

Author: aschwaighofer

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/DeadStoreElimination.swift

@@ -75,7 +75,7 @@ let deadStoreElimination = FunctionPass(name: "dead-store-elimination") {
 }
 
 private func tryEliminate(store: StoreInst, complexityBudget: inout Int, _ context: FunctionPassContext) {
-  if !store.hasValidOwnershipForDeadStoreElimination {
+  if !store.hasValidOwnershipForDeadStoreElimination || !store.source.type.shouldExpand(context) {
     return
   }
 

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/RedundantLoadElimination.swift

@@ -97,6 +97,9 @@ private func eliminateRedundantLoads(in function: Function, ignoreArrays: Bool,
         {
           continue
         }
+        if !load.type.shouldExpand(context) {
+           continue
+        }
         tryEliminate(load: load, complexityBudget: &complexityBudget, context)
       }
     }

SwiftCompilerSources/Sources/Optimizer/PassManager/Options.swift

@@ -20,6 +20,10 @@ struct Options {
     _bridged.enableStackProtection()
   }
 
+  var useAggressiveReg2MemForCodeSize : Bool {
+    _bridged.useAggressiveReg2MemForCodeSize()
+  }
+
   var enableMoveInoutStackProtection: Bool {
     _bridged.enableMoveInoutStackProtection()
   }

SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift

@@ -809,3 +809,12 @@ extension CheckedCastAddrBranchInst {
     }
   }
 }
+
+extension Type {
+  func shouldExpand(_ context: some Context) -> Bool {
+    if !context.options.useAggressiveReg2MemForCodeSize {
+      return true
+    }
+    return context._bridged.shouldExpand(self.bridged)
+  }
+}

include/swift/SILOptimizer/OptimizerBridging.h

@@ -261,6 +261,8 @@ struct BridgedPassContext {
   BRIDGED_INLINE bool optimizeMemoryAccesses(BridgedFunction f) const;
   BRIDGED_INLINE bool eliminateDeadAllocations(BridgedFunction f) const;
 
+  BRIDGED_INLINE bool shouldExpand(BridgedType type) const;
+
   // IRGen
 
   SwiftInt getStaticSize(BridgedType type) const;
@@ -372,6 +374,7 @@ struct BridgedPassContext {
     Unchecked = 2
   };
 
+  BRIDGED_INLINE bool useAggressiveReg2MemForCodeSize() const;
   BRIDGED_INLINE bool enableStackProtection() const;
   BRIDGED_INLINE bool hasFeature(BridgedFeature feature) const;
   BRIDGED_INLINE bool enableMoveInoutStackProtection() const;

include/swift/SILOptimizer/OptimizerBridgingImpl.h

@@ -556,11 +556,21 @@ bool BridgedPassContext::enableMoveInoutStackProtection() const {
   return mod->getOptions().EnableMoveInoutStackProtection;
 }
 
+bool BridgedPassContext::useAggressiveReg2MemForCodeSize() const {
+  swift::SILModule *mod = invocation->getPassManager()->getModule();
+  return mod->getOptions().UseAggressiveReg2MemForCodeSize;
+}
+
 BridgedPassContext::AssertConfiguration BridgedPassContext::getAssertConfiguration() const {
   swift::SILModule *mod = invocation->getPassManager()->getModule();
   return (AssertConfiguration)mod->getOptions().AssertConfig;
 }
 
+bool BridgedPassContext::shouldExpand(BridgedType ty) const {
+  swift::SILModule &mod = *invocation->getPassManager()->getModule();
+  return swift::shouldExpand(mod, ty.unbridged());
+}
+
 static_assert((int)BridgedPassContext::SILStage::Raw == (int)swift::SILStage::Raw);
 static_assert((int)BridgedPassContext::SILStage::Canonical == (int)swift::SILStage::Canonical);
 static_assert((int)BridgedPassContext::SILStage::Lowered == (int)swift::SILStage::Lowered);