[PATCH] D56587: Fix sign/zero extension in Dwarf expressions.

[Markus Lavin via Phabricator via llvm-commits]

markus added a comment.

In D56587#1354394 <https://reviews.llvm.org/D56587#1354394>, @vsk wrote:

> Thanks for the patch.
>
> t’s not obvious to me from skimming what the bug is with sign extension expressions. Could you describe what goes wrong, and maybe share a small program which shows the debugger behaving incorrectly?


What @bjope said and as for an example consider the following on x86

  #include <stdlib.h>
  short foo(short x) {
    int y = x;
    return y;
  }
  int main(int argc, char **argv) {
    return foo(strtol(argv[1], NULL, 0));
  }

Compiled in a somewhat contrived manner

  clang dbg.c -O0 -g3 -S -emit-llvm
  sed -i 's/optnone//' dbg.ll
  opt -mem2reg -instcombine dbg.ll -S -o dbg.opt.ll
  llc -O0 dbg.opt.ll -o dbg.s
  gcc dbg.s -o dbg

  gdb --args ./dbg 0xf000

  (gdb) b foo
  Breakpoint 1 at 0x400517: file dbg.c, line 4.
  (gdb) r
  Starting program: /repo/elavkje/llvm/my-dbg-test/dwarf-sext/dbg 0xf000
  
  Breakpoint 1, foo (x=-4096) at dbg.c:4
  4             return y;
  (gdb) whatis x
  type = short
  (gdb) p y
  $1 = -1
  (gdb) whatis y
  type = int
  (gdb)

It is clear that **y should not read as -1** at that point.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D56587/new/

https://reviews.llvm.org/D56587