Index: llvm/lib/Passes/PassBuilder.cpp
===================================================================
--- llvm/lib/Passes/PassBuilder.cpp
+++ llvm/lib/Passes/PassBuilder.cpp
@@ -703,14 +703,6 @@
   if (EnableSyntheticCounts && !PGOOpt)
     MPM.addPass(SyntheticCountsPropagation());
 
-  // Split out cold code. Splitting is done before inlining because 1) the most
-  // common kinds of cold regions can (a) be found before inlining and (b) do
-  // not grow after inlining, and 2) inhibiting inlining of cold code improves
-  // code size & compile time. Split after Mem2Reg to make code model estimates
-  // more accurate, but before InstCombine to allow it to clean things up.
-  if (EnableHotColdSplit && Phase != ThinLTOPhase::PostLink)
-    MPM.addPass(HotColdSplittingPass());
-
   // Require the GlobalsAA analysis for the module so we can query it within
   // the CGSCC pipeline.
   MPM.addPass(RequireAnalysisPass<GlobalsAA, Module>());
@@ -766,6 +758,12 @@
       createModuleToPostOrderCGSCCPassAdaptor(createDevirtSCCRepeatedPass(
           std::move(MainCGPipeline), MaxDevirtIterations)));
 
+  // Split out cold code. Splitting is done late to avoid hiding context from
+  // other optimizations and inadvertently regressing performance. The tradeoff
+  // is that this has a higher code size cost than splitting early.
+  if (EnableHotColdSplit && Phase != ThinLTOPhase::PreLink)
+    MPM.addPass(HotColdSplittingPass());
+
   return MPM;
 }
 
Index: llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -529,11 +529,6 @@
   if (DefaultOrPreLinkPipeline && !PrepareForThinLTOUsingPGOSampleProfile)
     addPGOInstrPasses(MPM);
 
-  // Split out cold code before inlining. See comment in the new PM
-  // (\ref buildModuleSimplificationPipeline).
-  if (EnableHotColdSplit && DefaultOrPreLinkPipeline)
-    MPM.add(createHotColdSplittingPass());
-
   // We add a module alias analysis pass here. In part due to bugs in the
   // analysis infrastructure this "works" in that the analysis stays alive
   // for the entire SCC pass run below.
@@ -730,6 +725,11 @@
     MPM.add(createConstantMergePass());     // Merge dup global constants
   }
 
+  // See comment in the new PM for justification of scheduling splitting at
+  // this stage (\ref buildModuleSimplificationPipeline).
+  if (EnableHotColdSplit && !(PrepareForLTO || PrepareForThinLTO))
+    MPM.add(createHotColdSplittingPass());
+
   if (MergeFunctions)
     MPM.add(createMergeFunctionsPass());
 
@@ -918,6 +918,11 @@
 
 void PassManagerBuilder::addLateLTOOptimizationPasses(
     legacy::PassManagerBase &PM) {
+  // See comment in the new PM for justification of scheduling splitting at
+  // this stage (\ref buildModuleSimplificationPipeline).
+  if (EnableHotColdSplit)
+    PM.add(createHotColdSplittingPass());
+
   // Delete basic blocks, which optimization passes may have killed.
   PM.add(createCFGSimplificationPass());
 
Index: llvm/test/Other/X86/lto-hot-cold-split.ll
===================================================================
--- llvm/test/Other/X86/lto-hot-cold-split.ll
+++ llvm/test/Other/X86/lto-hot-cold-split.ll
@@ -1,10 +1,10 @@
 ; RUN: opt -module-summary %s -o %t.bc
-; RUN: llvm-lto -hot-cold-split=true -thinlto-action=run %t.bc -debug-pass=Structure 2>&1 | FileCheck %s -check-prefix=OLDPM-THINLTO-POSTLINK-Os
+; RUN: llvm-lto -hot-cold-split=true -thinlto-action=run %t.bc -debug-pass=Structure 2>&1 | FileCheck %s -check-prefix=OLDPM-ANYLTO-POSTLINK-Os
+; RUN: llvm-lto -hot-cold-split=true %t.bc -debug-pass=Structure 2>&1 | FileCheck %s -check-prefix=OLDPM-ANYLTO-POSTLINK-Os
 
 ; REQUIRES: asserts
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-; OLDPM-THINLTO-POSTLINK-Os-LABEL: Pass Arguments
-; OLDPM-THINLTO-POSTLINK-Os-NOT: Hot Cold Splitting
+; OLDPM-ANYLTO-POSTLINK-Os: Hot Cold Splitting
Index: llvm/test/Other/new-pm-pgo.ll
===================================================================
--- llvm/test/Other/new-pm-pgo.ll
+++ llvm/test/Other/new-pm-pgo.ll
@@ -13,7 +13,6 @@
 ; GEN: Running pass: PGOInstrumentationGen
 ; USE: Running pass: PGOInstrumentationUse
 ; USE: Running pass: PGOIndirectCallPromotion
-; SPLIT: Running pass: HotColdSplittingPass
 ; USE: Running pass: PGOMemOPSizeOpt
 ; SAMPLE_USE_O: Running pass: ModuleToFunctionPassAdaptor<{{.*}}AddDiscriminatorsPass{{.*}}>
 ; SAMPLE_USE_PRE_LINK: Running pass: ModuleToFunctionPassAdaptor<{{.*}}AddDiscriminatorsPass{{.*}}>
@@ -27,6 +26,7 @@
 ; SAMPLE_USE_POST_LINK-NOT: Running pass: GlobalOptPass
 ; SAMPLE_USE_POST_LINK: Running pass: PGOIndirectCallPromotion
 ; SAMPLE_GEN: Running pass: ModuleToFunctionPassAdaptor<{{.*}}AddDiscriminatorsPass{{.*}}>
+; SPLIT: Running pass: HotColdSplittingPass
 
 define void @foo() {
   ret void
Index: llvm/test/Other/opt-hot-cold-split.ll
===================================================================
--- llvm/test/Other/opt-hot-cold-split.ll
+++ llvm/test/Other/opt-hot-cold-split.ll
@@ -5,18 +5,19 @@
 
 ; REQUIRES: asserts
 
-; Splitting should occur after Mem2Reg and should be followed by InstCombine.
+; Splitting should occur late.
 
-; DEFAULT-Os: Promote Memory to Register
 ; DEFAULT-Os: Hot Cold Splitting
-; DEFAULT-Os: Combine redundant instructions
+; DEFAULT-Os: Simplify the CFG
 
+; The new pass manager intentionally does not provide a way to differentiate
+; between an FullLTO prelink and a non-LTO pipeline. Therefore, expect splitting
+; to occur late in the FullLTO prelink and in the postlink.
 ; LTO-PRELINK-Os-LABEL: Starting llvm::Module pass manager run.
 ; LTO-PRELINK-Os: Running pass: {{.*}}PromotePass
 ; LTO-PRELINK-Os: Running pass: HotColdSplittingPass
 
 ; THINLTO-PRELINK-Os-LABEL: Running analysis: PassInstrumentationAnalysis
-; THINLTO-PRELINK-Os: Running pass: {{.*}}PromotePass
-; THINLTO-PRELINK-Os: Running pass: HotColdSplittingPass
+; THINLTO-PRELINK-Os-NOT: Running pass: HotColdSplittingPass
 
-; THINLTO-POSTLINK-Os-NOT: HotColdSplitting
+; THINLTO-POSTLINK-Os: HotColdSplitting
Index: llvm/test/Other/pass-pipelines.ll
===================================================================
--- llvm/test/Other/pass-pipelines.ll
+++ llvm/test/Other/pass-pipelines.ll
@@ -41,7 +41,6 @@
 ; PGOUSE:      Function Integration/Inlining
 ; PGOUSE: PGOInstrumentationUsePass
 ; PGOUSE: PGOIndirectCallPromotion
-; SPLIT: Hot Cold Splitting
 ; PGOUSE: CallGraph Construction
 ; CHECK-O2-NEXT: Globals Alias Analysis
 ; CHECK-O2-NEXT: Call Graph SCC Pass Manager
@@ -100,6 +99,7 @@
 ; the runtime unrolling though.
 ; CHECK-O2: Loop Pass Manager
 ; CHECK-O2-NEXT: Loop Invariant Code Motion
+; SPLIT: Hot Cold Splitting
 ; CHECK-O2: FunctionPass Manager
 ; CHECK-O2: Loop Pass Manager
 ; CHECK-O2-NEXT: Loop Sink