Remove debug metadata from copied instruction to prevent GPUModule verification failure

[singam-sanjay]

Summary

Remove debug metadata from instruction to be copied to prevent the source file's debug metadata being copied into GPUModule and eventually failing Module verification and ASM string codegeneration.

When copying the instruction onto the Module meant for the GPU, debug metadata attached to an instruction causes all related metadata to be pulled into the Module, including the DICompileUnit, which is not listed in llvm.dbg.cu of the Module. This fails the verification of the Module and generation of the ASM string.

The only debug metadata of the instruction, the DebugLoc, is unset by this patch.

This patch reattempts https://reviews.llvm.org/D35630 by targeting only those instructions that are to end up in a Module meant for the GPU.

[grosser]

Also, please update the summary to include the old commit message.

lib/CodeGen/BlockGenerators.cpp

249

Can you just check if Inst->getModule() != NewInst->getModule()

[singam-sanjay]

Simpler check to determine the destination Module of the cloned instruction.

[grosser]

LGTM

[singam-sanjay]

lib/CodeGen/BlockGenerators.cpp

249

Thanks for pointing this out ! I did think about this.

I had assumed that removing the DebugLoc from NewInst after inserting it into GPUModule wouldn't remove the Deubg metadata that came along with the instruction. But, moving the check before the insertion would have caused application to crash because NewInst isn't a part of a Module and NewInst->getModule() would seg fault. So, I went with an alternative approach.

[grosser]

lib/CodeGen/BlockGenerators.cpp

249

What is the alternative approach? Does the code as it is in phabricator work?

If NewInst->getModele does not work, you can always use Builder.GetInsertBlock()->getModule().

[singam-sanjay]

lib/CodeGen/BlockGenerators.cpp

249

The first diff was the alternative approach I was talking about. The code in phabricator does work.

lib/CodeGen/BlockGenerators.cpp

if (!NewOperand) {
              "Store instructions are always needed!");
       NewInst->deleteValue();
       return;
     }
 
     NewInst->replaceUsesOfWith(OldOperand, NewOperand);
   }
 
+
   Builder.Insert(NewInst);
   BBMap[Inst] = NewInst;
 
+  // When copying the instruction onto the Module meant for the GPU,
+  // debug metadata attached to an instruction causes all related
+  // metadata to be pulled into the Module. This includes the DICompileUnit,
+  // which will not be listed in llvm.dbg.cu of the Module since the Module
+  // doesn't contain one. This fails the verification of the Module and the
+  // subsequent generation of the ASM string.
+  if( NewInst->getModule() != Inst->getModule() )
+    NewInst->setDebugLoc(llvm::DebugLoc());
+
   if (!NewInst->getType()->isVoidTy())
     NewInst->setName("p_" + Inst->getName());
 }
 
 Value *
 BlockGenerator::generateLocationAccessed(ScopStmt &Stmt, MemAccInst Inst,
                                          ValueMapT &BBMap, LoopToScevMapT &LTS,
                                          isl_id_to_ast_expr *NewAccesses) {

test/GPGPU/debug-metadata-leak.ll

+; RUN: opt %loadPolly %s -polly-process-unprofitable -polly-codegen-ppcg -polly-acc-dump-kernel-ir \
+; RUN: | FileCheck --check-prefix=KERNEL-IR %s
+
+; REQUIRES: pollyacc
+
+; KERNEL-IR: define ptx_kernel void @FUNC_vec_add_1_SCOP_0_KERNEL_0(i8 addrspace(1)* %MemRef_arr, i32 %N) #0 {
+
+; The instruction marked <<<LeakyInst>>> is copied into the GPUModule,
+; with changes only to the parameters to access data on the device instead of
+; the host, i.e., MemRef_arr becomes polly.access.cast.MemRef_arr. Since the
+; instruction is annotated with a DILocation, copying the instruction also copies
+; the metadata into the GPUModule. This stops codegenerating the ptx_kernel by
+; failing the verification of the Module in GPUNodeBuilder::finalize, due to the
+; copied DICompileUnit not being listed in a llvm.dbg.cu which was neither copied
+; nor created.
+;
+; https://reviews.llvm.org/D35630 removes this debug metadata before the
+; instruction is copied to the GPUModule.
+; 
+; vec_add_1.c:
+;      void vec_add_1(int N, int arr[N]) {
+;        int i=0;
+;        for( i=0 ; i<N ; i++) arr[i] += 1;
+;      }
+;
+source_filename = "vec_add_1.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @vec_add_1(i32 %N, i32* %arr) !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %N, i64 0, metadata !13, metadata !16), !dbg !17
+  call void @llvm.dbg.value(metadata i32* %arr, i64 0, metadata !14, metadata !16), !dbg !18
+  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !16), !dbg !19
+  %tmp = sext i32 %N to i64, !dbg !20
+  br label %for.cond, !dbg !20
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  call void @llvm.dbg.value(metadata i32 undef, i64 0, metadata !15, metadata !16), !dbg !19
+  %cmp = icmp slt i64 %indvars.iv, %tmp, !dbg !22
+  br i1 %cmp, label %for.body, label %for.end, !dbg !24
+
+for.body:                                         ; preds = %for.cond
+  %arrayidx = getelementptr inbounds i32, i32* %arr, i64 %indvars.iv, !dbg !25
+  %tmp1 = load i32, i32* %arrayidx, align 4, !dbg !26, !tbaa !27
+  %add = add nsw i32 %tmp1, 1, !dbg !26    ;   <<<LeakyInst>>>
+  store i32 %add, i32* %arrayidx, align 4, !dbg !26, !tbaa !27
+  br label %for.inc, !dbg !25
+
+for.inc:                                          ; preds = %for.body
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !31
+  call void @llvm.dbg.value(metadata !2, i64 0, metadata !15, metadata !16), !dbg !19
+  br label %for.cond, !dbg !32, !llvm.loop !33
+
+for.end:                                          ; preds = %for.cond
+  ret void, !dbg !35
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 5.0.0 (http://llvm.org/git/clang.git 23e042ffe07a923db2dbebf4d2a3692c5a454fee) (http://llvm.org/git/llvm.git 39c5686a1f54884f12120927b1753a750fdb5e02)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "vec_add_1.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 5.0.0 (http://llvm.org/git/clang.git 23e042ffe07a923db2dbebf4d2a3692c5a454fee) (http://llvm.org/git/llvm.git 39c5686a1f54884f12120927b1753a750fdb5e02)"}
+!7 = distinct !DISubprogram(name: "vec_add_1", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !12)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10, !11}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64)
+!12 = !{!13, !14, !15}
+!13 = !DILocalVariable(name: "N", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!14 = !DILocalVariable(name: "arr", arg: 2, scope: !7, file: !1, line: 1, type: !11)
+!15 = !DILocalVariable(name: "i", scope: !7, file: !1, line: 2, type: !10)
+!16 = !DIExpression()
+!17 = !DILocation(line: 1, column: 20, scope: !7)
+!18 = !DILocation(line: 1, column: 27, scope: !7)
+!19 = !DILocation(line: 2, column: 7, scope: !7)
+!20 = !DILocation(line: 3, column: 8, scope: !21)
+!21 = distinct !DILexicalBlock(scope: !7, file: !1, line: 3, column: 3)
+!22 = !DILocation(line: 3, column: 15, scope: !23)
+!23 = distinct !DILexicalBlock(scope: !21, file: !1, line: 3, column: 3)
+!24 = !DILocation(line: 3, column: 3, scope: !21)
+!25 = !DILocation(line: 3, column: 25, scope: !23)
+!26 = !DILocation(line: 3, column: 32, scope: !23)
+!27 = !{!28, !28, i64 0}
+!28 = !{!"int", !29, i64 0}
+!29 = !{!"omnipotent char", !30, i64 0}
+!30 = !{!"Simple C/C++ TBAA"}
+!31 = !DILocation(line: 3, column: 21, scope: !23)
+!32 = !DILocation(line: 3, column: 3, scope: !23)
+!33 = distinct !{!33, !24, !34}
+!34 = !DILocation(line: 3, column: 35, scope: !21)
+!35 = !DILocation(line: 4, column: 1, scope: !7)