From e88096e9718adb26c45fe38453efa0e2e4629641 Mon Sep 17 00:00:00 2001
From: Erik Eckstein <eeckstein@apple.com>
Date: Mon, 6 Oct 2025 17:39:15 +0200
Subject: [PATCH 1/2] LoopInvariantCodeMotion: fix check for hoisting
 `load_borrow` instructions

We need to check aliasing for all kind of side-effect instructions, not just stores and destroys
---
 .../LoopInvariantCodeMotion.swift             | 26 ++++++++---------
 test/SILOptimizer/licm.sil                    | 28 +++++++++++++++++++
 2 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift
index 6683098f8db07..7072ff6ff0922 100644
--- a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift
+++ b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift
@@ -1206,23 +1206,21 @@ private extension ScopedInstruction {
     case is BeginApplyInst:
       return true // Has already been checked with other full applies.
     case let loadBorrowInst as LoadBorrowInst:
-      for case let destroyAddrInst as DestroyAddrInst in analyzedInstructions.loopSideEffects {
-        if context.aliasAnalysis.mayAlias(loadBorrowInst.address, destroyAddrInst.destroyedAddress) {
-          if !scope.contains(destroyAddrInst) {
-            return false
-          }
+      for sideEffectInst in analyzedInstructions.loopSideEffects {
+        if let endBorrow = sideEffectInst as? EndBorrowInst,
+           let begin = endBorrow.borrow as? LoadBorrowInst,
+           begin == self
+        {
+          continue
         }
-      }
-      
-      for storeInst in analyzedInstructions.stores {
-        if storeInst.mayWrite(toAddress: loadBorrowInst.address, context.aliasAnalysis) {
-          if !scope.contains(storeInst) {
-            return false
-          }
+        if sideEffectInst.mayWrite(toAddress: loadBorrowInst.address, context.aliasAnalysis),
+           !scope.contains(sideEffectInst)
+        {
+          return false
         }
       }
-      
-      fallthrough
+      return true
+
     case is BeginAccessInst:
       for fullApplyInst in analyzedInstructions.fullApplies {
         guard mayWriteToMemory && fullApplyInst.mayReadOrWrite(address: operands.first!.value, context.aliasAnalysis) ||
diff --git a/test/SILOptimizer/licm.sil b/test/SILOptimizer/licm.sil
index 60b23fe3321a3..4c1548d4043b9 100644
--- a/test/SILOptimizer/licm.sil
+++ b/test/SILOptimizer/licm.sil
@@ -1771,6 +1771,34 @@ bb3:
   return %r : $()
 }
 
+// CHECK-LABEL: sil [ossa] @dont_hoist_load_borrow :
+// CHECK:       bb1:
+// CHECK-NEXT:    copy_addr
+// CHECK-NEXT:    load_borrow
+// CHECK:       } // end sil function 'dont_hoist_load_borrow'
+sil [ossa] @dont_hoist_load_borrow : $@convention(thin) (@in_guaranteed String) -> () {
+bb0(%0 : $*String):
+  %1 = alloc_stack $String
+  br bb1
+
+bb1:
+  copy_addr %0 to [init] %1
+  %3 = load_borrow %1
+  fix_lifetime %3
+  end_borrow %3
+  %6 = load [take] %1
+  destroy_value %6
+  cond_br undef, bb2, bb3
+
+bb2:
+  br bb1
+
+bb3:
+  dealloc_stack %1
+  %r = tuple()
+  return %r : $()
+}
+
 // CHECK-LABEL: sil [ossa] @dont_hoist_struct :
 // CHECK:       bb1:
 // CHECK-NEXT:    struct $NonCopyable

From 55cdc31936820fd21e9aa27df0f3d4a37a8f67f8 Mon Sep 17 00:00:00 2001
From: Erik Eckstein <eeckstein@apple.com>
Date: Mon, 6 Oct 2025 17:54:59 +0200
Subject: [PATCH 2/2] LoopInvariantCodeMotion: a small refactoring

which is now possible as we removed the "fallthrough" from the previous case
---
 .../FunctionPasses/LoopInvariantCodeMotion.swift          | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift
index 7072ff6ff0922..ee4d03629e8c3 100644
--- a/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift
+++ b/SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LoopInvariantCodeMotion.swift
@@ -1221,10 +1221,10 @@ private extension ScopedInstruction {
       }
       return true
 
-    case is BeginAccessInst:
+    case let beginAccess as BeginAccessInst:
       for fullApplyInst in analyzedInstructions.fullApplies {
-        guard mayWriteToMemory && fullApplyInst.mayReadOrWrite(address: operands.first!.value, context.aliasAnalysis) ||
-              !mayWriteToMemory && fullApplyInst.mayWrite(toAddress: operands.first!.value, context.aliasAnalysis) else {
+        guard mayWriteToMemory && fullApplyInst.mayReadOrWrite(address: beginAccess.address, context.aliasAnalysis) ||
+              !mayWriteToMemory && fullApplyInst.mayWrite(toAddress: beginAccess.address, context.aliasAnalysis) else {
           continue
         }
 
@@ -1234,7 +1234,7 @@ private extension ScopedInstruction {
         }
       }
       
-      switch operands.first!.value.accessPath.base {
+      switch beginAccess.address.accessPath.base {
       case .class, .global:
         for sideEffect in analyzedInstructions.loopSideEffects where sideEffect.mayRelease {
           // Since a class might have a deinitializer, hoisting begin/end_access pair could violate