File:  [NetBSD Developer Wiki] / wikisrc / users / maya / vax-gcc.mdwn
Revision 1.10: download - view: text, annotated - select for diffs
Fri Aug 30 05:07:15 2019 UTC (5 months, 3 weeks ago) by maya
Branches: MAIN
CVS tags: HEAD
Moar notes

# Various GCC/vax issues and invesigation #

[WIP tree](gcc-mirror/)

## libgomp crash with -O2 ##
Repro:

    #!/bin/sh
    
    cat << EOF > oacc.i
    int a, b;
    int e() {
      short *c = 0;
      char d = c[a + 1];
      b = d;
      a += 2;
    }
    EOF
    vax--netbsdelf-gcc -O2 -c oacc.i

Asserts at emit-rtl.c:2310 gcc_assert (memory_address_addr_space_p (mode, addr, as));

NetBSD avoids it with a [local diff](https://github.com/NetBSD/src/commit/e437e96750193b86d0464965661f616e011056fa) to reload.c/dse.c.  
It looks like a real bug in vax_legitimate_address_p not handling some addressing modes.  
The code to handle offset(reg)[index] might be off: it doesn't like if neither xfoo0, xfoo1 are constant.

## unrecognizable insn with any optimization ##

Repro:

    #!/bin/sh

    cat << EOF > decl.ii
    struct a {
      long long *b() const;
    };
    template <typename> class d : a {
    public:
      template <typename e> d(e);
      long long f() const;
    };
    template <typename c> long long d<c>::f() const {
      int g;
      return b()[g];
    }
    int h;
    bool i() {
      d<int> j(h);
      return j.f();
    }
    EOF
    vax--netbsdelf-g++ -O2 -c decl.ii

This errors out with:

    $ env PATH=$PWD:$PATH ./xgcc -fno-use-linker-plugin -c -O2 ~/oacc/decl.ii -fno-tree-vectorize
    /home/fly/oacc/decl.ii: In function 'bool i()':
    /home/fly/oacc/decl.ii:17:1: error: unrecognizable insn:
       17 | }
          | ^
    (insn 13 12 14 2 (set (reg:SI 33)
            (subreg:SI (mem:DI (plus:SI (mult:SI (reg/v:SI 24 [ g ])
                            (const_int 8 [0x8]))
                        (reg/f:SI 23 [ _6 ])) [1 *_10+0 S8 A32]) 4)) "/home/fly/oacc/decl.ii":16:14 -1
         (nil))
    during RTL pass: vregs
    /home/fly/oacc/decl.ii:17:1: internal compiler error: in extract_insn, at recog.c:2310
    
Providing a trivial scheduling will avoid subregs of mem.  
However, this doesn't work for us. Our crash and mem subregs happen at a too early pass, most likely.

## DWARF ##

    flag_dwarf2_cfi_asm = 0;

is kind of a big deal. We should probably get rid of it, but [binutils hates that.](https://github.com/NetBSD/src/commit/1df57dce3744cf4743358b098728a0658b80b8fb)

    ld: warning: dynamic relocation to `?' in readonly section `.eh_frame'
    ld: warning: dynamic relocation to `?' in readonly section `.eh_frame'
    ld: warning: creating a DT_TEXTREL in a shared object
    ld: .eh_frame_hdr refers to overlapping FDEs
    ld: final link failed: bad value

[riscv seemed to share the issue](https://github.com/riscv/riscv-binutils-gdb/issues/76) and had fixed it.

## review comments ##

Jeff Law [provided some feedback](https://gcc.gnu.org/ml/gcc/2019-04/msg00281.html). More of it should be addressed.

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