[llvm-dwarfdump][Statistics] Distinguish parameters with same name or w/o a name

[krisb]

Summary

A few DW_TAG_formal_parameter's of the same function may have the same
name (e.g. variadic (template) functions) or don't have a name at all
(if the parameter isn't used inside the function body), but we still
need to be able to distinguish between them to get the correct number of 'total vars'
and 'availability' metric.

[aprantl]

Nice.

llvm/test/tools/llvm-dwarfdump/X86/statistics.ll

 ;   int (*fn)(int);
 ; } s;
 ;
 ; int __attribute__((always_inline)) square(int i) { return i * i; }
 ; int cube(int i) {
 ;   int squared = square(i);
 ;   return squared*i;
 ; }
+;
+; int boo(int, int) {}
 
 ; Following variables/arguments/members should be counted:
 ;     - GlobalConst,
 ;     - Global,
 ;     - s, s.constant,
 ;     - square::i,
 ;     - cube::i, cube::squared
+;     - boo::1, boo::2
 ; Skipped entities:
 ;     - declaration of test::a,
 ;     - non-constant member S:fn,
 ;     - arguments of S:fn.
 
-; CHECK: "unique source variables":7
+; CHECK: "unique source variables":9
 ; +1 extra inline i.
-; CHECK: "source variables":8
+; CHECK: "source variables":10
 ; -1 square::i
-; CHECK: "variables with location":7
+; CHECK: "variables with location":9
 ; CHECK: "scope bytes total":[[BYTES:[0-9]+]]
 ; Because of the dbg.value in the middle of the function, the pc range coverage
 ; must be below 100%.
 ; CHECK-NOT: "scope bytes covered":0
 ; CHECK-NOT "scope bytes covered":[[BYTES]]
 ; CHECK: "scope bytes covered":
 ; CHECK: "total function size":[[FUNCSIZE:[0-9]+]]
 ; CHECK: "total inlined function size":[[INLINESIZE:[0-9]+]]
entry:
   store i32 %mul.i, i32* %squared, align 4, !dbg !36
   %3 = load i32, i32* %squared, align 4, !dbg !41
   call void @llvm.dbg.value(metadata i32 %3, metadata !35, metadata !24), !dbg !36
   %4 = load i32, i32* %i.addr, align 4, !dbg !42
   %mul = mul nsw i32 %3, %4, !dbg !43
   ret i32 %mul, !dbg !44
 }
 
+; Function Attrs: noinline optnone uwtable
+define dso_local i32 @_Z3booii(i32 %0, i32 %1) !dbg !52 {
+entry:
+  %.addr = alloca i32, align 4
+  %.addr1 = alloca i32, align 4
+  store i32 %0, i32* %.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %.addr, metadata !55, metadata !DIExpression()), !dbg !56
+  store i32 %1, i32* %.addr1, align 4
+  call void @llvm.dbg.declare(metadata i32* %.addr1, metadata !57, metadata !DIExpression()), !dbg !58
+  ret i32 0, !dbg !58
+}
+
 attributes #0 = { alwaysinline nounwind ssp uwtable }
 attributes #1 = { nounwind readnone speculatable }
 attributes #2 = { noinline nounwind optnone ssp uwtable }
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!15, !16, !17, !18}
 !llvm.ident = !{!19}
 

 !44 = !DILocation(line: 11, column: 3, scope: !30)
 !45 = !DIDerivedType(tag: DW_TAG_member, name: "fn", scope: !11, file: !3, line: 5, baseType: !46, size: 64)
 !46 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !47, size: 64)
 !47 = !DISubroutineType(types: !22)
 !48 = !{!49}
 !49 = !DIImportedEntity(tag: DW_TAG_imported_declaration, scope: !2, entity: !50, file: !3, line: 2)
 !50 = !DIGlobalVariable(name: "a", linkageName: "_ZN4test1aE", scope: !51, file: !3, line: 2, type: !8, isLocal: false, isDefinition: false)
 !51 = !DINamespace(name: "test", scope: !2)
+!52 = distinct !DISubprogram(name: "boo", linkageName: "_Z3booii", scope: !3, file: !3, line: 10, type: !53, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !4)
+!53 = !DISubroutineType(types: !54)
+!54 = !{!8, !8, !8}
+!55 = !DILocalVariable(arg: 1, scope: !52, file: !3, line: 10, type: !8)
+!56 = !DILocation(line: 10, column: 12, scope: !52)
+!57 = !DILocalVariable(arg: 2, scope: !52, file: !3, line: 10, type: !8)
+!58 = !DILocation(line: 10, column: 17, scope: !52)

llvm/tools/llvm-dwarfdump/Statistics.cpp

static void collectStatsRecursive(DWARFDie Die, std::string FnPrefix,
   // Set InlineDepth correctly for child recursion
   if (IsFunction)
     InlineDepth = 0;
   else if (IsInlinedFunction)
     ++InlineDepth;
 
   // Traverse children.
   unsigned LexicalBlockIndex = 0;
+  unsigned FormalParameterIndex = 0;
   DWARFDie Child = Die.getFirstChild();
   while (Child) {
     std::string ChildVarPrefix = VarPrefix;
     if (Child.getTag() == dwarf::DW_TAG_lexical_block)
       ChildVarPrefix += toHex(LexicalBlockIndex++) + '.';
+    if (Child.getTag() == dwarf::DW_TAG_formal_parameter)
+      ChildVarPrefix += 'p' + toHex(FormalParameterIndex++) + '.';
 
     collectStatsRecursive(Child, FnPrefix, ChildVarPrefix, BytesInScope,
                           InlineDepth, FnStatMap, GlobalStats, LocStats);
     Child = Child.getSibling();
   }
 }
 
 /// Print machine-readable output.