[PATCH] D69886: [DebugInfo] Support for DW_OP_implicit_pointer (Post IR transformation phase)

[Jeremy Morse via Phabricator via llvm-commits]

jmorse added a comment.

Hi Alok,

Thanks for splitting up the patch and tests; I'm not very familiar with implicit pointers and I'm still working it through my mind, so I have a couple of questions if you'll bear with me. At the moment though, it looks like implicit-pointer dbg.value insts refer directly to DILocalVariables -- this will become a problem if the same function is inlined twice, as there's nothing to distinguish which inlining instance the dbg.value refers to. You can probably make a metadata pair of {DILocalVariable, DILocation} where the DILocation is the inlining location, and use that as the operand of the dbg.value instead. There should also be a test for multiple inlining instances too.

Looking at the tests, am I right in thinking that the "target" of the implicit pointer can change throughout the function? For example

  int a = 0, b = 1, c = 2;
  int *foo = &a;
  call();
  foo = &b;
  call();
  foo = &c;

Is it (theoretically) possible to describe promoted non-local variables with implicit pointers? LLVM will occasionally promote an in-memory value into a register, after which there's no way for current debuginfo to describe where it is.

The code looks like a good start, although I don't know anything about the DWARF backend.



================
Comment at: llvm/test/DebugInfo/dwarfdump-implicit_pointer_instcomb.ll:1
+; RUN: clang %s -O2 -gdwarf-5 -o %t.o
+; RUN: llvm-dwarfdump  %t.o | FileCheck %s
----------------
I don't believe running clang in an internal LLVM test is supported, this should probably be running llc -O2 -filetype=obj instead? Same with the other tests.


================
Comment at: llvm/test/DebugInfo/dwarfdump-implicit_pointer_instcomb.ll:46
+
+attributes #0 = { nofree norecurse nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
----------------
Assuming these attributes are un-necessary, they should be dropped as they can be an extra maintenance burden.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69886/new/

https://reviews.llvm.org/D69886