Bogus `-Wmaybe-uninitialized' warning with optimisation and `-Wall'

["Casper Ti. Vector" <caspervector at gmail dot com>]

Hello, the following source file (here called `gcc_bug.c') triggers
`-Wmaybe-uninitialized' when compiled with `-Os', `-O1' or stronger
optimisation, plus `-Wall':

------------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>

static int mk (int **a, int **b, int **c) {
	if (!(*a = malloc (sizeof (int)))) goto a_err;
	if (!(*b = malloc (sizeof (int)))) goto b_err;
	if (!(*c = malloc (sizeof (int)))) goto c_err;

	return 1; c_err:
	free (*b); b_err:
	free (*a); a_err:
	return 0;
}

static void fin (int *a, int *b, int *c) {
	free (c);
	free (b);
	free (a);
}

int main (void) {
	int *a, *b, *c, x, flag = mk (&a, &b, &c);
	while ((x = getchar ()) != -1) {
		if (flag) switch (x) {
		case 0:
			break;
		default:
			goto retn;
		} else if (x) goto retn;
	}
	retn:
	if (flag) fin (a, b, c);
	return 0;
}
------------------------------------------------------------------------

Attached are required output files:
* gcc_bug.txt: `gcc -v -save-temps -Wall -O2 -c gcc_bug.c -o gcc_bug.o'.
* gcc_bug.ii: `sed '/^#/d; /^[ \t]*$/d' < gcc_bug.i'.

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Attachment: gcc_bug.txt
Description: Text document

Attachment: gcc_bug.ii
Description: Text document