Revert "Introduce -fexperimental-loop-fuse to clang and flang (#142686)" #158764

vitalybuka · 2025-09-16T01:39:30Z

This reverts commit 895cda7.
And fix attempt: 06f671e.

Performance regressions and broken sanitizers, see #142686.

Created using spr 1.3.6

llvmbot · 2025-09-16T01:40:01Z

@llvm/pr-subscribers-flang-driver
@llvm/pr-subscribers-clang-codegen
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Vitaly Buka (vitalybuka)

Changes

This reverts commit 895cda7.
And fix attempt: 06f671e.

Performance regressions and broken sanitizers, see #142686.

Full diff: https://github.com/llvm/llvm-project/pull/158764.diff

15 Files Affected:

(modified) clang/include/clang/Basic/CodeGenOptions.def (-1)
(modified) clang/include/clang/Driver/Options.td (-4)
(modified) clang/lib/CodeGen/BackendUtil.cpp (-2)
(modified) clang/lib/Driver/ToolChains/Clang.cpp (-2)
(modified) clang/lib/Driver/ToolChains/Flang.cpp (-3)
(modified) clang/lib/Frontend/CompilerInvocation.cpp (-5)
(modified) clang/test/Driver/clang_f_opts.c (-9)
(modified) flang/docs/ReleaseNotes.md (-2)
(modified) flang/include/flang/Frontend/CodeGenOptions.def (-1)
(modified) flang/lib/Frontend/CompilerInvocation.cpp (-3)
(modified) flang/lib/Frontend/FrontendActions.cpp (-1)
(removed) flang/test/Driver/loop-fuse.f90 (-17)
(modified) llvm/include/llvm/Passes/PassBuilder.h (-3)
(modified) llvm/lib/Passes/PassBuilderPipelines.cpp (+1-7)
(modified) llvm/tools/opt/NewPMDriver.cpp (-4)

diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def
index 872f73ebf3810..fda0da99b60c0 100644
--- a/clang/include/clang/Basic/CodeGenOptions.def
+++ b/clang/include/clang/Basic/CodeGenOptions.def
@@ -322,7 +322,6 @@ CODEGENOPT(TimeTrace         , 1, 0, Benign) ///< Set when -ftime-trace is enabl
 VALUE_CODEGENOPT(TimeTraceGranularity, 32, 500, Benign) ///< Minimum time granularity (in microseconds),
                                                         ///< traced by time profiler
 CODEGENOPT(InterchangeLoops  , 1, 0, Benign) ///< Run loop-interchange.
-CODEGENOPT(FuseLoops         , 1, 0, Benign) ///< Run loop-fusion.
 CODEGENOPT(UnrollLoops       , 1, 0, Benign) ///< Control whether loops are unrolled.
 CODEGENOPT(RerollLoops       , 1, 0, Benign) ///< Control whether loops are rerolled.
 CODEGENOPT(NoUseJumpTables   , 1, 0, Benign) ///< Set when -fno-jump-tables is enabled.
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index def7c09d58cfb..54cc1e986b601 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4304,10 +4304,6 @@ def floop_interchange : Flag<["-"], "floop-interchange">, Group<f_Group>,
   HelpText<"Enable the loop interchange pass">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>,
   HelpText<"Disable the loop interchange pass">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
-defm experimental_loop_fusion
-    : OptInCC1FFlag<"experimental-loop-fusion", "Enable", "Disable",
-                    "Enable the loop fusion pass",
-                    [ClangOption, FlangOption, FC1Option]>;
 def funroll_loops : Flag<["-"], "funroll-loops">, Group<f_Group>,
   HelpText<"Turn on loop unroller">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 def fno_unroll_loops : Flag<["-"], "fno-unroll-loops">, Group<f_Group>,
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 8c99af2bdff83..3f095c03397fd 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -896,7 +896,6 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
   PipelineTuningOptions PTO;
   PTO.LoopUnrolling = CodeGenOpts.UnrollLoops;
   PTO.LoopInterchange = CodeGenOpts.InterchangeLoops;
-  PTO.LoopFusion = CodeGenOpts.FuseLoops;
   // For historical reasons, loop interleaving is set to mirror setting for loop
   // unrolling.
   PTO.LoopInterleaving = CodeGenOpts.UnrollLoops;
@@ -1332,7 +1331,6 @@ runThinLTOBackend(CompilerInstance &CI, ModuleSummaryIndex *CombinedIndex,
   Conf.SampleProfile = std::move(SampleProfile);
   Conf.PTO.LoopUnrolling = CGOpts.UnrollLoops;
   Conf.PTO.LoopInterchange = CGOpts.InterchangeLoops;
-  Conf.PTO.LoopFusion = CGOpts.FuseLoops;
   // For historical reasons, loop interleaving is set to mirror setting for loop
   // unrolling.
   Conf.PTO.LoopInterleaving = CGOpts.UnrollLoops;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index c9377e23086c5..a72bdedd7317b 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6861,8 +6861,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                   options::OPT_fno_unroll_loops);
   Args.AddLastArg(CmdArgs, options::OPT_floop_interchange,
                   options::OPT_fno_loop_interchange);
-  Args.addOptInFlag(CmdArgs, options::OPT_fexperimental_loop_fusion,
-                    options::OPT_fno_experimental_loop_fusion);
 
   Args.AddLastArg(CmdArgs, options::OPT_fstrict_flex_arrays_EQ);
 
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 12e510ab1562d..2118c67dedc54 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -156,9 +156,6 @@ void Flang::addCodegenOptions(const ArgList &Args,
       !stackArrays->getOption().matches(options::OPT_fno_stack_arrays))
     CmdArgs.push_back("-fstack-arrays");
 
-  Args.addOptInFlag(CmdArgs, options::OPT_fexperimental_loop_fusion,
-                    options::OPT_fno_experimental_loop_fusion);
-
   handleInterchangeLoopsArgs(Args, CmdArgs);
   handleVectorizeLoopsArgs(Args, CmdArgs);
   handleVectorizeSLPArgs(Args, CmdArgs);
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 422375240bab6..761310813f787 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1680,9 +1680,6 @@ void CompilerInvocationBase::GenerateCodeGenArgs(const CodeGenOptions &Opts,
   else
     GenerateArg(Consumer, OPT_fno_loop_interchange);
 
-  if (Opts.FuseLoops)
-    GenerateArg(Consumer, OPT_fexperimental_loop_fusion);
-
   if (!Opts.BinutilsVersion.empty())
     GenerateArg(Consumer, OPT_fbinutils_version_EQ, Opts.BinutilsVersion);
 
@@ -2004,8 +2001,6 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
                    (Opts.OptimizationLevel > 1));
   Opts.InterchangeLoops =
       Args.hasFlag(OPT_floop_interchange, OPT_fno_loop_interchange, false);
-  Opts.FuseLoops = Args.hasFlag(OPT_fexperimental_loop_fusion,
-                                OPT_fno_experimental_loop_fusion, false);
   Opts.BinutilsVersion =
       std::string(Args.getLastArgValue(OPT_fbinutils_version_EQ));
 
diff --git a/clang/test/Driver/clang_f_opts.c b/clang/test/Driver/clang_f_opts.c
index 581b031eb7a86..ee7ded265769b 100644
--- a/clang/test/Driver/clang_f_opts.c
+++ b/clang/test/Driver/clang_f_opts.c
@@ -52,15 +52,6 @@
 // CHECK-INTERCHANGE-LOOPS: "-floop-interchange"
 // CHECK-NO-INTERCHANGE-LOOPS: "-fno-loop-interchange"
 
-// RUN: %clang -### -S -fexperimental-loop-fusion %s 2>&1 | FileCheck -check-prefix=CHECK-FUSE-LOOPS %s
-// CHECK-FUSE-LOOPS: "-fexperimental-loop-fusion"
-//
-// RUN: %clang -c -fexperimental-loop-fusion -mllvm -print-pipeline-passes -O3 %s -o /dev/null 2>&1 | FileCheck --check-prefixes=LOOP-FUSION-ON %s
-// RUN: %clang -c -mllvm -print-pipeline-passes -O3 %s -o /dev/null 2>&1 | FileCheck --check-prefixes=LOOP-FUSION-OFF %s
-
-// LOOP-FUSION-ON: loop-fusion
-// LOOP-FUSION-OFF-NOT: loop-fusion
-
 // RUN: %clang -### -S -fprofile-sample-accurate %s 2>&1 | FileCheck -check-prefix=CHECK-PROFILE-SAMPLE-ACCURATE %s
 // CHECK-PROFILE-SAMPLE-ACCURATE: "-fprofile-sample-accurate"
 
diff --git a/flang/docs/ReleaseNotes.md b/flang/docs/ReleaseNotes.md
index 6a285f829053b..c9623ea08c4e6 100644
--- a/flang/docs/ReleaseNotes.md
+++ b/flang/docs/ReleaseNotes.md
@@ -35,8 +35,6 @@ page](https://llvm.org/releases/).
 
 ## New Compiler Flags
 
-* -fexperimental-loop-fusion is now recognized by flang.
-
 ## Windows Support
 
 ## Fortran Language Changes in Flang
diff --git a/flang/include/flang/Frontend/CodeGenOptions.def b/flang/include/flang/Frontend/CodeGenOptions.def
index f09159962883f..22f778c5d3d38 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.def
+++ b/flang/include/flang/Frontend/CodeGenOptions.def
@@ -43,7 +43,6 @@ CODEGENOPT(StackArrays, 1, 0) ///< -fstack-arrays (enable the stack-arrays pass)
 CODEGENOPT(VectorizeLoop, 1, 0) ///< Enable loop vectorization.
 CODEGENOPT(VectorizeSLP, 1, 0) ///< Enable SLP vectorization.
 CODEGENOPT(InterchangeLoops, 1, 0) ///< Enable loop interchange.
-CODEGENOPT(FuseLoops, 1, 0) ///< Enable loop fusion.
 CODEGENOPT(LoopVersioning, 1, 0) ///< Enable loop versioning.
 CODEGENOPT(UnrollLoops, 1, 0) ///< Enable loop unrolling
 CODEGENOPT(AliasAnalysis, 1, 0) ///< Enable alias analysis pass
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index a00e568bb4a54..c7dbfc46f432c 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -280,9 +280,6 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
   if (args.getLastArg(clang::driver::options::OPT_floop_interchange))
     opts.InterchangeLoops = 1;
 
-  if (args.getLastArg(clang::driver::options::OPT_fexperimental_loop_fusion))
-    opts.FuseLoops = 1;
-
   if (args.getLastArg(clang::driver::options::OPT_vectorize_loops))
     opts.VectorizeLoop = 1;
 
diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index 23cc1e63e773d..3bef6b1c31825 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cpp
@@ -958,7 +958,6 @@ void CodeGenAction::runOptimizationPipeline(llvm::raw_pwrite_stream &os) {
     si.getTimePasses().setOutStream(ci.getTimingStreamLLVM());
   pto.LoopUnrolling = opts.UnrollLoops;
   pto.LoopInterchange = opts.InterchangeLoops;
-  pto.LoopFusion = opts.FuseLoops;
   pto.LoopInterleaving = opts.UnrollLoops;
   pto.LoopVectorization = opts.VectorizeLoop;
   pto.SLPVectorization = opts.VectorizeSLP;
diff --git a/flang/test/Driver/loop-fuse.f90 b/flang/test/Driver/loop-fuse.f90
deleted file mode 100644
index ddfd9065e0fd4..0000000000000
--- a/flang/test/Driver/loop-fuse.f90
+++ /dev/null
@@ -1,17 +0,0 @@
-! RUN: %flang -### -S -fexperimental-loop-fusion %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-FUSE %s
-! RUN: %flang -### -S -fno-experimental-loop-fusion %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! RUN: %flang -### -S -O0 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! RUN: %flang -### -S -O1 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! RUN: %flang -### -S -O2 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! RUN: %flang -### -S -O3 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! RUN: %flang -### -S -Os %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! RUN: %flang -### -S -Oz %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE %s
-! CHECK-LOOP-FUSE: "-fexperimental-loop-fusion"
-! CHECK-NO-LOOP-FUSE-NOT: "-fexperimental-loop-fusion"
-! RUN: %flang_fc1 -emit-llvm -O2 -fexperimental-loop-fusion -mllvm -print-pipeline-passes -o /dev/null %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-FUSE-PASS %s
-! RUN: %flang_fc1 -emit-llvm -O2 -fno-experimental-loop-fusion -mllvm -print-pipeline-passes -o /dev/null %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-FUSE-PASS %s
-! CHECK-LOOP-FUSE-PASS: loop-fusion
-! CHECK-NO-LOOP-FUSE-PASS-NOT: loop-fusion
-
-program test
-end program
diff --git a/llvm/include/llvm/Passes/PassBuilder.h b/llvm/include/llvm/Passes/PassBuilder.h
index 2742ec1b71b7e..9cdb7ca7dbc9b 100644
--- a/llvm/include/llvm/Passes/PassBuilder.h
+++ b/llvm/include/llvm/Passes/PassBuilder.h
@@ -65,9 +65,6 @@ class PipelineTuningOptions {
   /// false.
   bool LoopInterchange;
 
-  /// Tuning option to enable/disable loop fusion. Its default value is false.
-  bool LoopFusion;
-
   /// Tuning option to forget all SCEV loops in LoopUnroll. Its default value
   /// is that of the flag: `-forget-scev-loop-unroll`.
   bool ForgetAllSCEVInLoopUnroll;
diff --git a/llvm/lib/Passes/PassBuilderPipelines.cpp b/llvm/lib/Passes/PassBuilderPipelines.cpp
index 79642e650ac83..98821bb1408a7 100644
--- a/llvm/lib/Passes/PassBuilderPipelines.cpp
+++ b/llvm/lib/Passes/PassBuilderPipelines.cpp
@@ -104,7 +104,6 @@
 #include "llvm/Transforms/Scalar/LoopDeletion.h"
 #include "llvm/Transforms/Scalar/LoopDistribute.h"
 #include "llvm/Transforms/Scalar/LoopFlatten.h"
-#include "llvm/Transforms/Scalar/LoopFuse.h"
 #include "llvm/Transforms/Scalar/LoopIdiomRecognize.h"
 #include "llvm/Transforms/Scalar/LoopInstSimplify.h"
 #include "llvm/Transforms/Scalar/LoopInterchange.h"
@@ -1552,11 +1551,6 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   OptimizePM.addPass(createFunctionToLoopPassAdaptor(
       std::move(LPM), /*UseMemorySSA=*/false, /*UseBlockFrequencyInfo=*/false));
 
-  // FIXME: This may not be the right place in the pipeline.
-  // We need to have the data to support the right place.
-  if (PTO.LoopFusion)
-    OptimizePM.addPass(LoopFusePass());
-
   // Distribute loops to allow partial vectorization.  I.e. isolate dependences
   // into separate loop that would otherwise inhibit vectorization.  This is
   // currently only performed for loops marked with the metadata
@@ -2361,4 +2355,4 @@ AAManager PassBuilder::buildDefaultAAPipeline() {
 bool PassBuilder::isInstrumentedPGOUse() const {
   return (PGOOpt && PGOOpt->Action == PGOOptions::IRUse) ||
          !UseCtxProfile.empty();
-}
+}
\ No newline at end of file
diff --git a/llvm/tools/opt/NewPMDriver.cpp b/llvm/tools/opt/NewPMDriver.cpp
index 0c991b71a6b26..b9b8929a0f703 100644
--- a/llvm/tools/opt/NewPMDriver.cpp
+++ b/llvm/tools/opt/NewPMDriver.cpp
@@ -60,9 +60,6 @@ cl::opt<bool> VerifyEachDebugInfoPreserve(
     cl::desc("Start each pass with collecting and end it with checking of "
              "debug info preservation."));
 
-static cl::opt<bool> EnableLoopFusion("enable-loopfusion", cl::init(false),
-                                      cl::Hidden,
-                                      cl::desc("Enable the LoopFuse Pass"));
 cl::opt<std::string>
     VerifyDIPreserveExport("verify-di-preserve-export",
                    cl::desc("Export debug info preservation failures into "
@@ -449,7 +446,6 @@ bool llvm::runPassPipeline(
   // option has been enabled.
   PTO.LoopUnrolling = !DisableLoopUnrolling;
   PTO.UnifiedLTO = UnifiedLTO;
-  PTO.LoopFusion = EnableLoopFusion;
   PassBuilder PB(TM, PTO, P, &PIC);
   registerEPCallbacks(PB);

vitalybuka · 2025-09-16T01:48:13Z

CC @alazarev

kasuga-fj

(As for one of the reviewers of PR #142686) LGTM, thanks!

[𝘀𝗽𝗿] initial version

7fefd08

Created using spr 1.3.6

vitalybuka requested a review from sebpop September 16, 2025 01:40

vitalybuka added the skip-precommit-approval PR for CI feedback, not intended for review label Sep 16, 2025

vitalybuka enabled auto-merge (squash) September 16, 2025 01:41

kasuga-fj approved these changes Sep 16, 2025

View reviewed changes

vitalybuka merged commit cedceeb into main Sep 16, 2025
18 checks passed

vitalybuka deleted the users/vitalybuka/spr/revert-introduce-fexperimental-loop-fuse-to-clang-and-flang-142686-2 branch September 16, 2025 02:30

vitalybuka mentioned this pull request Sep 16, 2025

Introduce -fexperimental-loop-fuse to clang and flang #142686

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Revert "Introduce -fexperimental-loop-fuse to clang and flang (#142686)" #158764

Revert "Introduce -fexperimental-loop-fuse to clang and flang (#142686)" #158764

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Revert "Introduce -fexperimental-loop-fuse to clang and flang (#142686)" #158764

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