[Bug c++/2972] -Wuninitialized could warn about uninitialized member variable usage in constructors

["manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=2972

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #21 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #20)
> Perhaps a better alternative is to warn only if the uninitialized member is
> used in a mem-initializer. Then, when building the constructor call, mark
> the uninitialized members somehow as uninitialized for the middle-end, and
> let the middle-end handle the cases in the body of the constructor. The
> first part would already fix PR19808. The second part will fix this bug with
> fewer false positives than the proposed patch.

And this comment gives some ideas:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19808#c9

Richard B, you say that: "using <error-mark> [for marking undefined memory] is
just a random (and probably bad) idea."  Intuitively this seems more scalable,
since one could propagate the undefined value like VRP does.

The other alternative "Introducing a SSA name default definition for A (even
though not of register type)", however, seems possible already. no? We do
already check for default definitions in virtual operands, tree-ssa-uninit.c
says:

      /* For memory the only cheap thing we can do is see if we
         have a use of the default def of the virtual operand.

So what is missing here?
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From: "itay at phobotic dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/63408] New: GCC emits incorrect FMA instruction
Date: Mon, 29 Sep 2014 15:15:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idc408

            Bug ID: 63408
           Summary: GCC emits incorrect FMA instruction
           Product: gcc
           Version: 4.8.4
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: itay at phobotic dot com

When compiling the following function

float f(float a, int b)
{
    return a - (((float)b / 0x7fffffff) * 100);
}

with the following command-line options

arm-none-eabi-gcc -O2 -mthumb -mfpu=fpv4-sp-d16 -mfloat-abi=softfp
-mcpu=cortex-m4

I get this code for f:

    fmsr    s14, r1    @ int
    flds    s15, .L2
    vcvt.f32.s32    s14, s14, #31
    fmsr    s13, r0
    vfma.f32    s13, s14, s15
    fmrs    r0, s13
    bx    lr
.L3:
    .align    2
.L2:
    .word    1120403456

The resulting code clearly adds the parenthesized expression to a rather than
subtracting it.

Replacing the minus sign with a plus sign results in the same code.