https://bugs.llvm.org/show_bug.cgi?id=40319
Bug ID: 40319
Summary: [DebugInfo] X86DiscriminateMemOps inserts potentially
misleading line numbers
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: jeremy.morse.l...@gmail.com
CC: craig.top...@gmail.com, davi...@google.com,
douglas_y...@playstation.sony.com,
greg.bedw...@sony.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, mtro...@google.com,
spatel+l...@rotateright.com, w...@google.com
Hi, if one compiles the following sample with llvm/clang r351192 and the
command line "clang -x c++ test.cpp -fdebug-info-for-profiling
-fstack-protector -o a.out -O0 -g -c",
--------8<--------
int foo (int input_param)
{
int array1[input_param];
array1[0]=18;
return array1[0];
}
-------->8--------
And then examine the line tables with dwarfdump -l a.out:
--------8<--------
0x00000000 [ 2, 0] NS uri: "/home/jmorse/fdebug.cpp"
0x00000011 [ 1, 0] NS PE DI=0x2
0x00000015 [ 1, 0] DI=0x4
0x00000018 [ 3,16] NS
0x0000001d [ 3, 5]
0x00000020 [ 3, 5] DI=0x2
0x00000024 [ 3, 5] DI=0x4
...
-------->8--------
We have the line numbers going backwards at the start of the function (two to
one to three). This is due to the x86-discriminate-memops pass picking the
default line number to instrument memory operations with as being the start of
the function. (See ReferenceDI in X86DiscriminateMemOps.cpp).
These line numbers are potentially misleading IMHO -- would we be able to use a
zero line number by default instead? According to the DWARF spec this
corresponds to compiler-generated code and will be ignored by debuggers. That
way X86DiscriminateMemOps won't have any affect on debugging, and the change
(AFAIK) will have no effect on its operation.
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