[llvm-reduce] Attempt to strip debug info

[aeubanks]

Summary

I often run llvm-reduce on IR that contains debug info, this prevents an
extra step of opt -passes=strip I do every time and will result in a
lot less invalid reductions around debug metadata.

[aeubanks]

llvm/tools/llvm-reduce/deltas/StripDebugInfo.cpp

22

not sure if this is the best way to detect presence of debug info

[arsenm]

Isn't the first step in the existing debug info reducer to try deleting all of it?

[aeubanks]

In D136208#3866723, @arsenm wrote:

Isn't the first step in the existing debug info reducer to try deleting all of it?

the existing di-metadata pass is very specific, it only tries to remove array entries debug info metadata arrays. it doesn't do anything with !dbg attached to instructions, the corresponding DI metadata nodes, the global named !llvm.dbg.* named metadata, and dbg intrinsics

[arsenm]

In D136208#3866733, @aeubanks wrote:

In D136208#3866723, @arsenm wrote:

Isn't the first step in the existing debug info reducer to try deleting all of it?

the existing di-metadata pass is very specific, it only tries to remove array entries debug info metadata arrays. it doesn't do anything with !dbg attached to instructions, the corresponding DI metadata nodes, the global named !llvm.dbg.* named metadata, and dbg intrinsics

But the metadata reduction looks at individual instructions. Doesn't di-metadata + metadata cover this?

[aeubanks]

In D136208#3866741, @arsenm wrote:

In D136208#3866733, @aeubanks wrote:

In D136208#3866723, @arsenm wrote:

Isn't the first step in the existing debug info reducer to try deleting all of it?

the existing di-metadata pass is very specific, it only tries to remove array entries debug info metadata arrays. it doesn't do anything with !dbg attached to instructions, the corresponding DI metadata nodes, the global named !llvm.dbg.* named metadata, and dbg intrinsics

But the metadata reduction looks at individual instructions. Doesn't di-metadata + metadata cover this?

I'm not sure that di-metadata can handle all types of debug info structures (I think I've seen cases where not all debug info is removed even though the striped IR still is interesting, although I'm having a hard time remembering a specific example). But even if it did, we get lots of invalid reductions (due to various verifier constraints) that would be avoided if we just stripped everything to begin with, speeding things up a lot.

[arsenm]

I don't really know enough about debug info to dispute this, but I don't find working around invalid reductions in the existing passes a compelling reason to special case eliminating all the debug info

[dblaikie]

llvm/tools/llvm-reduce/deltas/StripDebugInfo.cpp

25

Looks like this also strips function/global variable names and register names - any chance we don't want to strip those too? Should we call this llvm-reduce pass "StripSymbols" rather than "stripDebugInfo" to be consistent with the underlying pass and its slightly different/broader semantics?

[aeubanks]

only strip debug info

[dblaikie]

Sounds good to me :)

[aeubanks]

In D136208#3871694, @arsenm wrote:

I don't really know enough about debug info to dispute this, but I don't find working around invalid reductions in the existing passes a compelling reason to special case eliminating all the debug info

there are random constraints on debug info metadata, e.g. https://reviews.llvm.org/D135492. while it's possible to handle all of these in all the different passes, I don't think it's necessarily worth the effort if most of the time debug info doesn't matter anyway

llvm/test/tools/llvm-reduce/strip-debug-info.ll

+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=strip-debug-info --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefix=CHECK-FINAL %s --input-file=%t
+
+; CHECK-INTERESTINGNESS: define i32 @main
+; CHECK-FINAL: define i32 @main
+; CHECK-FINAL-NOT: !dbg
+; CHECK-FINAL-NOT: call {{.*}}llvm.dbg
+; CHECK-FINAL-NOT: !llvm.dbg
+; CHECK-FINAL-NOT: = !DI
+
+define i32 @main() !dbg !4 {
+entry:
+  %retval = alloca i32, align 4
+  %a = alloca i8, align 1
+  store i32 0, ptr %retval, align 4
+  call void @llvm.dbg.declare(metadata ptr %a, metadata !10, metadata !DIExpression()), !dbg !12
+  store i8 0, ptr %a, align 1, !dbg !12
+  ret i32 0, !dbg !13
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 16.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "/tmp/a.c", directory: "/tmp", checksumkind: CSK_MD5, checksum: "2ed6e287521b82331926229153026511")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "main", scope: !5, file: !5, line: 4, type: !6, scopeLine: 4, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !9)
+!5 = !DIFile(filename: "/tmp/a.c", directory: "", checksumkind: CSK_MD5, checksum: "2ed6e287521b82331926229153026511")
+!6 = !DISubroutineType(types: !7)
+!7 = !{!8}
+!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !{}
+!10 = !DILocalVariable(name: "a", scope: !4, file: !5, line: 6, type: !11)
+!11 = !DIBasicType(name: "_Bool", size: 8, encoding: DW_ATE_boolean)
+!12 = !DILocation(line: 6, column: 8, scope: !4)
+!13 = !DILocation(line: 7, column: 2, scope: !4)

llvm/tools/llvm-reduce/CMakeLists.txt

add_llvm_tool(llvm-reduce
   deltas/ReduceIRReferences.cpp
   deltas/ReduceVirtualRegisters.cpp
   deltas/ReduceRegisterMasks.cpp
   deltas/ReduceRegisterDefs.cpp
   deltas/ReduceRegisterUses.cpp
   deltas/ReduceUsingSimplifyCFG.cpp
   deltas/RunIRPasses.cpp
   deltas/SimplifyInstructions.cpp
+  deltas/StripDebugInfo.cpp
   llvm-reduce.cpp
 
   DEPENDS
   intrinsics_gen
   )

llvm/tools/llvm-reduce/DeltaManager.cpp

 #include "deltas/ReduceRegisterDefs.h"
 #include "deltas/ReduceRegisterMasks.h"
 #include "deltas/ReduceRegisterUses.h"
 #include "deltas/ReduceSpecialGlobals.h"
 #include "deltas/ReduceUsingSimplifyCFG.h"
 #include "deltas/ReduceVirtualRegisters.h"
 #include "deltas/RunIRPasses.h"
 #include "deltas/SimplifyInstructions.h"
+#include "deltas/StripDebugInfo.h"
 #include "llvm/Support/CommandLine.h"
 
 using namespace llvm;
 
 using SmallStringSet = SmallSet<StringRef, 8>;
 
 extern cl::OptionCategory LLVMReduceOptions;
 static cl::list<std::string>
     DeltaPasses("delta-passes",
                 cl::desc("Delta passes to run, separated by commas. By "
                          "default, run all delta passes."),
                 cl::cat(LLVMReduceOptions), cl::CommaSeparated);
 
 static cl::list<std::string>
     SkipDeltaPasses("skip-delta-passes",
                     cl::desc("Delta passes to not run, separated by commas. By "
                              "default, run all delta passes."),
                     cl::cat(LLVMReduceOptions), cl::CommaSeparated);
 
 #define DELTA_PASSES                                                           \
   do {                                                                         \
+    DELTA_PASS("strip-debug-info", stripDebugInfoDeltaPass)                    \
     DELTA_PASS("functions", reduceFunctionsDeltaPass)                          \
     DELTA_PASS("function-bodies", reduceFunctionBodiesDeltaPass)               \
     DELTA_PASS("special-globals", reduceSpecialGlobalsDeltaPass)               \
     DELTA_PASS("aliases", reduceAliasesDeltaPass)                              \
     DELTA_PASS("basic-blocks", reduceBasicBlocksDeltaPass)                     \
     DELTA_PASS("global-values", reduceGlobalValuesDeltaPass)                   \
     DELTA_PASS("global-objects", reduceGlobalObjectsDeltaPass)                 \
     DELTA_PASS("global-initializers", reduceGlobalsInitializersDeltaPass)      \

llvm/tools/llvm-reduce/deltas/StripDebugInfo.h

+//===- StripDebugInfo.h -----------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLVM_REDUCE_DELTAS_STRIPDEBUGINFO_H
+#define LLVM_TOOLS_LLVM_REDUCE_DELTAS_STRIPDEBUGINFO_H
+
+#include "Delta.h"
+
+namespace llvm {
+void stripDebugInfoDeltaPass(TestRunner &Test);
+} // namespace llvm
+
+#endif

llvm/tools/llvm-reduce/deltas/StripDebugInfo.cpp

+//===- StripDebugInfo.cpp -------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "StripDebugInfo.h"
+#include "Delta.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/Metadata.h"
+
+using namespace llvm;
+
+/// Removes all aliases aren't inside any of the
+/// desired Chunks.
+static void stripDebugInfoImpl(Oracle &O, Module &Program) {
+  bool HasDebugInfo = any_of(Program.named_metadata(), [](NamedMDNode &NMD) {
+    return NMD.getName().startswith("llvm.dbg.");
+  });
+  if (HasDebugInfo && !O.shouldKeep())
+    StripDebugInfo(Program);
+}
+
+void llvm::stripDebugInfoDeltaPass(TestRunner &Test) {
+  runDeltaPass(Test, stripDebugInfoImpl, "Stripping Debug Info");
+}

llvm/utils/gn/secondary/llvm/tools/llvm-reduce/BUILD.gn

sources = [
     "deltas/ReduceRegisterDefs.cpp",
     "deltas/ReduceRegisterMasks.cpp",
     "deltas/ReduceRegisterUses.cpp",
     "deltas/ReduceSpecialGlobals.cpp",
     "deltas/ReduceUsingSimplifyCFG.cpp",
     "deltas/ReduceVirtualRegisters.cpp",
     "deltas/RunIRPasses.cpp",
     "deltas/SimplifyInstructions.cpp",
+    "deltas/StripDebugInfo.cpp",
     "deltas/Utils.cpp",
     "llvm-reduce.cpp",
   ]
 }