tsan: don't consider debug calls as calls

[dvyukov]

Summary

Tsan pass does 2 optimizations based on presence of calls:

1. Don't emit function entry/exit callbacks if there are no calls

and no memory accesses.

2. Combine read/write of the same variable if there are no

intervening calls.
However, all debug info is represented as CallInst as well
and thus effectively disables these optimizations.
Don't consider debug info calls as calls.

[glider]

LGTM

llvm/lib/Transforms/Instrumentation/ThreadSanitizer.cpp

bool ThreadSanitizer::sanitizeFunction(Function &F,
 
   // Traverse all instructions, collect loads/stores/returns, check for calls.
   for (auto &BB : F) {
     for (auto &Inst : BB) {
       if (isAtomic(&Inst))
         AtomicAccesses.push_back(&Inst);
       else if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst))
         LocalLoadsAndStores.push_back(&Inst);
-      else if (isa<CallInst>(Inst) || isa<InvokeInst>(Inst)) {
+      else if ((isa<CallInst>(Inst) && !isa<DbgInfoIntrinsic>(Inst)) ||
+               isa<InvokeInst>(Inst)) {
         if (CallInst *CI = dyn_cast<CallInst>(&Inst))
           maybeMarkSanitizerLibraryCallNoBuiltin(CI, &TLI);
         if (isa<MemIntrinsic>(Inst))
           MemIntrinCalls.push_back(&Inst);
         HasCalls = true;
         chooseInstructionsToInstrument(LocalLoadsAndStores, AllLoadsAndStores,
                                        DL);
       }

llvm/test/Instrumentation/ThreadSanitizer/debug_calls.ll

+; RUN: opt < %s -tsan -S | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @Increment(i32* nocapture %0) local_unnamed_addr sanitize_thread !dbg !7 {
+  call void @llvm.dbg.value(metadata i32* %0, metadata !14, metadata !DIExpression()), !dbg !16
+  %2 = load i32, i32* %0, align 4, !dbg !17, !tbaa !18
+  call void @llvm.dbg.value(metadata i32 %2, metadata !15, metadata !DIExpression()), !dbg !16
+  %3 = add nsw i32 %2, 1, !dbg !22
+  store i32 %3, i32* %0, align 4, !dbg !23, !tbaa !18
+  ret void, !dbg !24
+}
+; CHECK-LABEL: define void @Increment
+; CHECK-NOT: __tsan_read4
+; CHECK: __tsan_write4
+; CHECK: ret void
+
+define i32 @NoAccesses(i32 %0) local_unnamed_addr sanitize_thread !dbg !25 {
+  call void @llvm.dbg.value(metadata i32 %0, metadata !29, metadata !DIExpression()), !dbg !30
+  %2 = add nsw i32 %0, 1, !dbg !31
+  ret i32 %2, !dbg !32
+}
+; CHECK-LABEL: define i32 @NoAccesses
+; CHECK-NOT: __tsan_func_entry
+; CHECK-NOT: __tsan_func_exit
+; CHECK: ret i32
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang"}
+!7 = distinct !DISubprogram(name: "Increment", scope: !8, file: !8, line: 1, type: !9, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !13)
+!8 = !DIFile(filename: "test.c", directory: "")
+!9 = !DISubroutineType(types: !10)
+!10 = !{null, !11}
+!11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !{!14, !15}
+!14 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !8, line: 1, type: !11)
+!15 = !DILocalVariable(name: "x", scope: !7, file: !8, line: 2, type: !12)
+!16 = !DILocation(line: 0, scope: !7)
+!17 = !DILocation(line: 2, column: 11, scope: !7)
+!18 = !{!19, !19, i64 0}
+!19 = !{!"int", !20, i64 0}
+!20 = !{!"omnipotent char", !21, i64 0}
+!21 = !{!"Simple C/C++ TBAA"}
+!22 = !DILocation(line: 3, column: 10, scope: !7)
+!23 = !DILocation(line: 3, column: 6, scope: !7)
+!24 = !DILocation(line: 4, column: 1, scope: !7)
+!25 = distinct !DISubprogram(name: "NoAccesses", scope: !8, file: !8, line: 6, type: !26, scopeLine: 6, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !28)
+!26 = !DISubroutineType(types: !27)
+!27 = !{!12, !12}
+!28 = !{!29}
+!29 = !DILocalVariable(name: "a", arg: 1, scope: !25, file: !8, line: 6, type: !12)
+!30 = !DILocation(line: 0, scope: !25)
+!31 = !DILocation(line: 7, column: 12, scope: !25)
+!32 = !DILocation(line: 7, column: 3, scope: !25)