Safely generate new loop metadata node

dmpots · dmpots · commit a4817871d233 · 2014-11-07T21:44:18.000Z
Polly was accidently modifying a debug info metadata node when attempting to generate a new unique metadata node for the loop id. The problem was that we had dwarf metadata that referred to a metadata node with a null value, like this: !6 = ... some dwarf metadata referring to !7 ... !7 = {null} When we attempt to generate a new metadata node, we reserve the first space for self-referential node by setting the first argument to null and then mutating the node later to refer to itself. However, because the nodes are uniqued based on pointer values, when we get the new metadata node it actually referred to an existing node (!7 in the example). When we went to modify the metadata to point to itself, we were accidently mutating the dwarf metatdata. We ended up in this situation: !6 = ... some dwarf metadata referring to !7 ... !7 = {!7} and this causes an assert when generating the debug info. The fix is simple, we just need to use a unique value when getting a new metadata node. The MDNode::getTemporary() provides exactly the API we need (and it is used in clang to generate the unique nodes). Differential Revision: http://reviews.llvm.org/D6174 llvm-svn: 221550
diff --git a/polly/lib/CodeGen/IRBuilder.cpp b/polly/lib/CodeGen/IRBuilder.cpp
@@ -34,7 +34,10 @@ static MDNode *getID(LLVMContext &Ctx, Value *arg0 = nullptr,
                      Value *arg1 = nullptr) {
   MDNode *ID;
   SmallVector<Value *, 3> Args;
-  Args.push_back(nullptr);
+  // Use a temporary node to safely create a unique pointer for the first arg.
+  MDNode *TempNode = MDNode::getTemporary(Ctx, None);
+  // Reserve operand 0 for loop id self reference.
+  Args.push_back(TempNode);
 
   if (arg0)
     Args.push_back(arg0);
@@ -43,6 +46,7 @@ static MDNode *getID(LLVMContext &Ctx, Value *arg0 = nullptr,
 
   ID = MDNode::get(Ctx, Args);
   ID->replaceOperandWith(0, ID);
+  MDNode::deleteTemporary(TempNode);
   return ID;
 }
 
diff --git a/polly/test/Isl/CodeGen/LoopParallelMD/do_not_mutate_debug_info.ll b/polly/test/Isl/CodeGen/LoopParallelMD/do_not_mutate_debug_info.ll
@@ -0,0 +1,71 @@
+; This test checks that we do not accidently mutate the debug info when
+; inserting loop parallel metadata.
+; RUN: opt %loadPolly < %s  -S -polly -polly-codegen-isl -polly-ast-detect-parallel | FileCheck %s
+; CHECK-NOT: !7 = metadata !{metadata !7}
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@A = common global i32* null, align 8
+
+; Function Attrs: nounwind uwtable
+define void @foo() {
+entry:
+  tail call void @llvm.dbg.value(metadata !18, i64 0, metadata !9, metadata !19), !dbg !20
+  %0 = load i32** @A, align 8, !dbg !21, !tbaa !23
+  br label %for.body, !dbg !27
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i32* %0, i64 %indvars.iv, !dbg !21
+  %1 = load i32* %arrayidx, align 4, !dbg !21, !tbaa !30
+  %add = add nsw i32 %1, 1, !dbg !21
+  store i32 %add, i32* %arrayidx, align 4, !dbg !21, !tbaa !30
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !27
+  %exitcond = icmp eq i64 %indvars.iv, 1, !dbg !27
+  br i1 %exitcond, label %for.end, label %for.body, !dbg !27
+
+for.end:                                          ; preds = %for.body
+  ret void, !dbg !32
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!15, !16}
+!llvm.ident = !{!17}
+
+!0 = metadata !{metadata !"0x11\0012\00clang version 3.6.0 \001\00\000\00\001", metadata !1, metadata !2, metadata !2, metadata !3, metadata !12, metadata !2} ; [ DW_TAG_compile_unit ] [/local/mnt/workspace/build/tip-Release/t2.c] [DW_LANG_C99]
+!1 = metadata !{metadata !"t2.c", metadata !"/local/mnt/workspace/build/tip-Release"}
+!2 = metadata !{}
+!3 = metadata !{metadata !4}
+!4 = metadata !{metadata !"0x2e\00foo\00foo\00\003\000\001\000\000\000\001\003", metadata !1, metadata !5, metadata !6, null, void ()* @foo, null, null, metadata !8} ; [ DW_TAG_subprogram ] [line 3] [def] [foo]
+!5 = metadata !{metadata !"0x29", metadata !1}    ; [ DW_TAG_file_type ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!6 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", null, null, null, metadata !7, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{null}
+!8 = metadata !{metadata !9}
+!9 = metadata !{metadata !"0x100\00i\004\000", metadata !10, metadata !5, metadata !11} ; [ DW_TAG_auto_variable ] [i] [line 4]
+!10 = metadata !{metadata !"0xb\004\003\000", metadata !1, metadata !4} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!11 = metadata !{metadata !"0x24\00int\000\0032\0032\000\000\005", null, null} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!12 = metadata !{metadata !13}
+!13 = metadata !{metadata !"0x34\00A\00A\00\002\000\001", null, metadata !5, metadata !14, i32** @A, null} ; [ DW_TAG_variable ] [A] [line 2] [def]
+!14 = metadata !{metadata !"0xf\00\000\0064\0064\000\000", null, null, metadata !11} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from int]
+!15 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
+!16 = metadata !{i32 2, metadata !"Debug Info Version", i32 2}
+!17 = metadata !{metadata !"clang version 3.6.0 "}
+!18 = metadata !{i32 0}
+!19 = metadata !{metadata !"0x102"}               ; [ DW_TAG_expression ]
+!20 = metadata !{i32 4, i32 12, metadata !10, null}
+!21 = metadata !{i32 5, i32 5, metadata !22, null}
+!22 = metadata !{metadata !"0xb\004\003\001", metadata !1, metadata !10} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!23 = metadata !{metadata !24, metadata !24, i64 0}
+!24 = metadata !{metadata !"any pointer", metadata !25, i64 0}
+!25 = metadata !{metadata !"omnipotent char", metadata !26, i64 0}
+!26 = metadata !{metadata !"Simple C/C++ TBAA"}
+!27 = metadata !{i32 4, i32 3, metadata !28, null}
+!28 = metadata !{metadata !"0xb\002", metadata !1, metadata !29} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!29 = metadata !{metadata !"0xb\001", metadata !1, metadata !22} ; [ DW_TAG_lexical_block ] [/local/mnt/workspace/build/tip-Release/t2.c]
+!30 = metadata !{metadata !31, metadata !31, i64 0}
+!31 = metadata !{metadata !"int", metadata !25, i64 0}
+!32 = metadata !{i32 6, i32 1, metadata !4, null}
