[llvm-locstats] Avoid the loc stats for the cases with no scope bytes coverage

[djtodoro]

Summary

If the total number of PC range bytes in each variable's enclosing scope ('scope bytes total') is 0, we will have division by zero.

llvm/test/tools/llvm-locstats/no_scope_bytes.ll

+; UNSUPPORTED: system-windows
+; REQUIRES: x86-registered-target
+; RUN: llc %s -o %t0.o -filetype=obj
+; RUN: %llvm-locstats %t0.o | FileCheck %s --check-prefix=LOCSTATS
+;
+; LOCSTATS: No scope bytes found.
+;
+; This is based on the following reproducer:
+;
+; int fn() {
+;  return 0;
+; }
+;
+; ModuleID = 'test.c'
+source_filename = "test.c"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+; Function Attrs: norecurse nounwind readnone uwtable
+define dso_local i32 @fn() local_unnamed_addr !dbg !7 {
+entry:
+  ret i32 0, !dbg !11
+}
+
+!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 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 10.0.0"}
+!7 = distinct !DISubprogram(name: "fn", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 2, column: 3, scope: !7)

llvm/utils/llvm-locstats/llvm-locstats.py

def locstats_output(
   variables_total,
   variables_total_locstats,
   variables_with_loc,
   scope_bytes_covered,
   scope_bytes,
   variables_coverage_map
   ):
 
+  if scope_bytes == 0:
+    print ('No scope bytes found.')
+    sys.exit(0)
+
   pc_ranges_covered = int(ceil(scope_bytes_covered * 100.0)
               / scope_bytes)
   variables_coverage_per_map = {}
   for cov_bucket in coverage_buckets():
     variables_coverage_per_map[cov_bucket] = \
       int(ceil(variables_coverage_map[cov_bucket] * 100.0) \
                / variables_total_locstats)