[Clang][Driver] Add an option to control loop-interchange #125830

sjoerdmeijer · 2025-02-05T10:12:42Z

This introduces options -floop-interchange and -fno-loop-interchange to enable/disable the loop-interchange pass. This is part of the work that tries to get that pass enabled by default (#124911), where it was remarked that a user facing option to control this would be convenient to have. The option name is the same as GCC's.

llvmbot · 2025-02-05T10:13:22Z

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Sjoerd Meijer (sjoerdmeijer)

Changes

This introduces options -floop-interchange and -fno-loop-interchange to enable/disable the loop-interchange pass. This is part of the work that tries to get that pass enabled by default (#124911), where it was remarked that a user facing option to control this would be convenient to have. The option name is the same as GCC's.

Full diff: https://github.com/llvm/llvm-project/pull/125830.diff

3 Files Affected:

(modified) clang/include/clang/Driver/Options.td (+3)
(modified) clang/lib/Driver/ToolChains/Clang.cpp (+10)
(modified) clang/test/Driver/clang_f_opts.c (+7)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index df705104d9ea314..3132f8946c6d3be 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4073,6 +4073,9 @@ defm assumptions : BoolFOption<"assumptions",
           "Disable codegen and compile-time checks for C++23's [[assume]] attribute">,
   PosFlag<SetTrue>>;
 
+def floop_interchange : Flag<["-"], "floop-interchange">, Group<f_Group>,
+  HelpText<"Enable the loop interchange pass">;
+def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>;
 def fvectorize : Flag<["-"], "fvectorize">, Group<f_Group>,
   HelpText<"Enable the loop vectorization passes">;
 def fno_vectorize : Flag<["-"], "fno-vectorize">, Group<f_Group>;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 33f08cf28feca18..757093c3d3a5cfa 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -7619,6 +7619,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.addOptOutFlag(CmdArgs, options::OPT_fgnu_inline_asm,
                      options::OPT_fno_gnu_inline_asm);
 
+  // Handle -floop-interchange
+  if (Arg *A = Args.getLastArg(options::OPT_floop_interchange,
+                               options::OPT_fno_loop_interchange)) {
+    CmdArgs.push_back("-mllvm");
+    if (A->getOption().matches(options::OPT_floop_interchange))
+      CmdArgs.push_back("-enable-loopinterchange=true");
+    else
+      CmdArgs.push_back("-enable-loopinterchange=false");
+  }
+
   // Enable vectorization per default according to the optimization level
   // selected. For optimization levels that want vectorization we use the alias
   // option to simplify the hasFlag logic.
diff --git a/clang/test/Driver/clang_f_opts.c b/clang/test/Driver/clang_f_opts.c
index 38f25898c955682..908d592928b01fc 100644
--- a/clang/test/Driver/clang_f_opts.c
+++ b/clang/test/Driver/clang_f_opts.c
@@ -156,6 +156,13 @@
 // CHECK-VECTORIZE: "-vectorize-loops"
 // CHECK-NO-VECTORIZE-NOT: "-vectorize-loops"
 
+// RUN: %clang -### -S -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE %s
+// RUN: %clang -### -S -fno-loop-interchange -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE %s
+// RUN: %clang -### -S -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE %s
+// RUN: %clang -### -S -floop-interchange -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE %s
+// CHECK-INTERCHANGE: "-mllvm" "-enable-loopinterchange=true"
+// CHECK-NO-INTERCHANGE: "-mllvm" "-enable-loopinterchange=false"
+
 // RUN: %clang -### -S -fslp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-SLP-VECTORIZE %s
 // RUN: %clang -### -S -fno-slp-vectorize -fslp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-SLP-VECTORIZE %s
 // RUN: %clang -### -S -fno-slp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-NO-SLP-VECTORIZE %s

llvmbot · 2025-02-05T10:13:22Z

@llvm/pr-subscribers-clang-driver

Author: Sjoerd Meijer (sjoerdmeijer)

Changes

This introduces options -floop-interchange and -fno-loop-interchange to enable/disable the loop-interchange pass. This is part of the work that tries to get that pass enabled by default (#124911), where it was remarked that a user facing option to control this would be convenient to have. The option name is the same as GCC's.

Full diff: https://github.com/llvm/llvm-project/pull/125830.diff

3 Files Affected:

(modified) clang/include/clang/Driver/Options.td (+3)
(modified) clang/lib/Driver/ToolChains/Clang.cpp (+10)
(modified) clang/test/Driver/clang_f_opts.c (+7)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index df705104d9ea31..3132f8946c6d3b 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4073,6 +4073,9 @@ defm assumptions : BoolFOption<"assumptions",
           "Disable codegen and compile-time checks for C++23's [[assume]] attribute">,
   PosFlag<SetTrue>>;
 
+def floop_interchange : Flag<["-"], "floop-interchange">, Group<f_Group>,
+  HelpText<"Enable the loop interchange pass">;
+def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>;
 def fvectorize : Flag<["-"], "fvectorize">, Group<f_Group>,
   HelpText<"Enable the loop vectorization passes">;
 def fno_vectorize : Flag<["-"], "fno-vectorize">, Group<f_Group>;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 33f08cf28feca1..757093c3d3a5cf 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -7619,6 +7619,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.addOptOutFlag(CmdArgs, options::OPT_fgnu_inline_asm,
                      options::OPT_fno_gnu_inline_asm);
 
+  // Handle -floop-interchange
+  if (Arg *A = Args.getLastArg(options::OPT_floop_interchange,
+                               options::OPT_fno_loop_interchange)) {
+    CmdArgs.push_back("-mllvm");
+    if (A->getOption().matches(options::OPT_floop_interchange))
+      CmdArgs.push_back("-enable-loopinterchange=true");
+    else
+      CmdArgs.push_back("-enable-loopinterchange=false");
+  }
+
   // Enable vectorization per default according to the optimization level
   // selected. For optimization levels that want vectorization we use the alias
   // option to simplify the hasFlag logic.
diff --git a/clang/test/Driver/clang_f_opts.c b/clang/test/Driver/clang_f_opts.c
index 38f25898c95568..908d592928b01f 100644
--- a/clang/test/Driver/clang_f_opts.c
+++ b/clang/test/Driver/clang_f_opts.c
@@ -156,6 +156,13 @@
 // CHECK-VECTORIZE: "-vectorize-loops"
 // CHECK-NO-VECTORIZE-NOT: "-vectorize-loops"
 
+// RUN: %clang -### -S -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE %s
+// RUN: %clang -### -S -fno-loop-interchange -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE %s
+// RUN: %clang -### -S -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE %s
+// RUN: %clang -### -S -floop-interchange -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE %s
+// CHECK-INTERCHANGE: "-mllvm" "-enable-loopinterchange=true"
+// CHECK-NO-INTERCHANGE: "-mllvm" "-enable-loopinterchange=false"
+
 // RUN: %clang -### -S -fslp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-SLP-VECTORIZE %s
 // RUN: %clang -### -S -fno-slp-vectorize -fslp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-SLP-VECTORIZE %s
 // RUN: %clang -### -S -fno-slp-vectorize %s 2>&1 | FileCheck -check-prefix=CHECK-NO-SLP-VECTORIZE %s

Meinersbur · 2025-02-05T11:31:54Z

The other optimzation pass options (unrolll, vectorize, ...) are implemented in PipelineTuningOptions and CodeGenOptions.def. Do it the same way?

sjoerdmeijer · 2025-02-06T11:05:52Z

The other optimzation pass options (unrolll, vectorize, ...) are implemented in PipelineTuningOptions and CodeGenOptions.def. Do it the same way?

Thanks for the review and suggestion @Meinersbur, that's now implemented in the latest revision.

Meinersbur · 2025-02-06T11:10:11Z

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -316,6 +312,7 @@ PipelineTuningOptions::PipelineTuningOptions() {
  LoopVectorization = true;
  SLPVectorization = false;
  LoopUnrolling = true;
+  LoopInterchange = false;


The default of LoopInterchange could be initialized with EnableLoopInterchange, as done by MergeFunctions = EnableMergeFunction.

Not important for me, but someone might want to keep -mllvm -enable-loopinterchange working, e.g. for non-Clang drivers.

Good idea, that's now fixed.

github-actions · 2025-02-06T12:13:22Z

✅ With the latest revision this PR passed the C/C++ code formatter.

kasuga-fj · 2025-02-06T13:31:47Z

I'm not familiar with these parts, but the code looks good to me.

This is a bit off topic, but do you have any opinion on adding a pragma for interchange like other loop optimizations do? I think it can sometimes be useful if we can enable/disable the interchange for each loop, but I think there are a few things to consider if we introduce it, such as the behavior when the pragma is specified on a non-outermost loop. What do you think?

madhur13490

LGTM. Considering code-formatting issues will be fixed before committing.

Meinersbur

LGTM

Dont forget clang-format (#125830 (comment))

This introduces options -floop-interchange and -fno-loop-interchange to enable/disable the loop-interchange pass. This is part of the work that tries to get that pass enabled by default (llvm#124911), where it was remarked that a user facing option to control this would be convenient to have. The option (name) is the same as GCC's.

sjoerdmeijer · 2025-02-07T10:36:55Z

This is a bit off topic, but do you have any opinion on adding a pragma for interchange like other loop optimizations do? I think it can sometimes be useful if we can enable/disable the interchange for each loop, but I think there are a few things to consider if we introduce it, such as the behavior when the pragma is specified on a non-outermost loop. What do you think?

Yeah, I see the use case for that, I think that makes sense. And OpenMP6 for example, introduces a directive for interchange. Please propose a patch if you're interested in pursuing this.

Meinersbur · 2025-02-07T10:48:23Z

The OpenMP pragma conceptually applies interchange in the frontend, with syntactical requirements for the loops it applies to.

kasuga-fj · 2025-02-07T15:23:36Z

Thanks for the comments. I'll try to work on it in the near future.

This introduces options `-floop-interchange` and `-fno-loop-interchange` to enable/disable the loop-interchange pass. This is part of the work that tries to get that pass enabled by default (llvm#124911), where it was remarked that a user facing option to control this would be convenient to have. The option name is the same as GCC's.

LoopInterchange has several heuristic functions to determine if exchanging two loops is profitable or not. Whether or not to use each heuristic and the order in which to use them were fixed, but #125830 allows them to be changed internally at will. This patch adds a new option to control them via the compiler option. The previous patch also added an option to prioritize the vectorization heuristic. This patch also removes it to avoid conflicts between it and the newly introduced one, e.g., both `-loop-interchange-prioritize-vectorization=1` and `-loop-interchange-profitabilities='cache,vectorization'` are specified.

#133664) LoopInterchange has several heuristic functions to determine if exchanging two loops is profitable or not. Whether or not to use each heuristic and the order in which to use them were fixed, but #125830 allows them to be changed internally at will. This patch adds a new option to control them via the compiler option. The previous patch also added an option to prioritize the vectorization heuristic. This patch also removes it to avoid conflicts between it and the newly introduced one, e.g., both `-loop-interchange-prioritize-vectorization=1` and `-loop-interchange-profitabilities='cache,vectorization'` are specified.

sjoerdmeijer requested review from sebpop, Meinersbur, madhur13490, CongzheUalberta and kasuga-fj February 5, 2025 10:12

llvmbot added clang Clang issues not falling into any other category clang:driver 'clang' and 'clang++' user-facing binaries. Not 'clang-cl' labels Feb 5, 2025

sjoerdmeijer force-pushed the clang-f-interchange branch from 24b8e28 to da944d7 Compare February 6, 2025 11:01

llvmbot added clang:frontend Language frontend issues, e.g. anything involving "Sema" clang:codegen IR generation bugs: mangling, exceptions, etc. labels Feb 6, 2025

sjoerdmeijer force-pushed the clang-f-interchange branch from da944d7 to 72c1ccc Compare February 6, 2025 11:04

Meinersbur reviewed Feb 6, 2025

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sjoerdmeijer force-pushed the clang-f-interchange branch from 72c1ccc to 1a655eb Compare February 6, 2025 12:09

madhur13490 approved these changes Feb 6, 2025

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Meinersbur approved these changes Feb 6, 2025

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kasuga-fj approved these changes Feb 7, 2025

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sjoerdmeijer force-pushed the clang-f-interchange branch from 1a655eb to 45aa8d5 Compare February 7, 2025 09:09

sjoerdmeijer merged commit 612df14 into llvm:main Feb 7, 2025
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sjoerdmeijer deleted the clang-f-interchange branch February 7, 2025 10:31

kasuga-fj mentioned this pull request Feb 14, 2025

debug-only not working for loop interchange pass #127022

Closed

kasuga-fj mentioned this pull request Mar 31, 2025

[LoopInterchange] Add an option to control the cost heuristics applied #133664

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[Clang][Driver] Add an option to control loop-interchange #125830

[Clang][Driver] Add an option to control loop-interchange #125830

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[Clang][Driver] Add an option to control loop-interchange #125830

[Clang][Driver] Add an option to control loop-interchange #125830

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