diff --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -724,7 +724,8 @@
   LPM1.addPass(LoopRotatePass(Level != OptimizationLevel::Oz));
   // TODO: Investigate promotion cap for O1.
   LPM1.addPass(LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap));
-  LPM1.addPass(SimpleLoopUnswitchPass(/* NonTrivial */ true));
+  LPM1.addPass(
+      SimpleLoopUnswitchPass(/* NonTrivial */ Level == OptimizationLevel::O3));
   LPM2.addPass(LoopIdiomRecognizePass());
   LPM2.addPass(IndVarSimplifyPass());
 
diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -2906,6 +2906,10 @@
   if (!NonTrivial && !EnableNonTrivialUnswitch)
     return false;
 
+  // Skip non-trivial unswitching for optsize functions.
+  if (L.getHeader()->getParent()->hasOptSize())
+    return false;
+
   // For non-trivial unswitching, because it often creates new loops, we rely on
   // the pass manager to iterate on the loops rather than trying to immediately
   // reach a fixed point. There is no substantial advantage to iterating
diff --git a/llvm/test/Transforms/SimpleLoopUnswitch/pipeline.ll b/llvm/test/Transforms/SimpleLoopUnswitch/pipeline.ll
--- a/llvm/test/Transforms/SimpleLoopUnswitch/pipeline.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/pipeline.ll
@@ -1,12 +1,15 @@
-; RUN: opt < %s -S -passes="default<O1>" | FileCheck %s -check-prefix=O1
-; RUN: opt < %s -S -passes="default<O2>" | FileCheck %s -check-prefix=O2
+; RUN: opt < %s -S -passes="default<O1>" | FileCheck %s -check-prefixes=TRIVIAL,CHECK
+; RUN: opt < %s -S -passes="default<O2>" | FileCheck %s -check-prefixes=TRIVIAL,CHECK
+; RUN: opt < %s -S -passes="default<O3>" | FileCheck %s -check-prefixes=NONTRIVIAL,CHECK
+; RUN: opt < %s -S -passes="default<Os>" | FileCheck %s -check-prefixes=TRIVIAL,CHECK
+; RUN: opt < %s -S -passes="default<Oz>" | FileCheck %s -check-prefixes=TRIVIAL,CHECK
 
 declare i32 @a()
 declare i32 @b()
 declare i32 @c()
 
-; O1-NOT: loop_begin.us:
-; O2: loop_begin.us:
+; TRIVIAL-NOT: loop_begin.us:
+; NONTRIVIAL: loop_begin.us:
 
 define i32 @test1(i1* %ptr, i1 %cond1, i1 %cond2) {
 entry:
@@ -37,3 +40,34 @@
 loop_exit:
   ret i32 0
 }
+
+; CHECK-NOT: loop2_begin.us:
+define i32 @test2(i1* %ptr, i1 %cond1, i1 %cond2) optsize {
+entry:
+  br label %loop2_begin
+
+loop2_begin:
+  br i1 %cond1, label %loop2_a, label %loop2_b
+
+loop2_a:
+  call i32 @a()
+  br label %latch2
+
+loop2_b:
+  br i1 %cond2, label %loop2_b_a, label %loop2_b_b
+
+loop2_b_a:
+  call i32 @b()
+  br label %latch2
+
+loop2_b_b:
+  call i32 @c()
+  br label %latch2
+
+latch2:
+  %v = load i1, i1* %ptr
+  br i1 %v, label %loop2_begin, label %loop2_exit
+
+loop2_exit:
+  ret i32 0
+}