[Bug middle-end/104522] ICE: in real_to_decimal_for_mode with -O -fdump-tree-all-details and long double

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104522

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jsm28 at gcc dot gnu.org

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is that native_interpret_real produces something that's not
printable.  For MODE_COMPOSITE_P types we have code that verifies
back-and-forth
conversion - when we enable that we get until RTL which happens to generate

(insn # 0 0 2 (set (reg:XF 8 st)
        (mem/u/c:XF (symbol_ref/u:DI ("*.LC1") [flags 0x2]) [  S16 A128]))
"t.c":9:6# {*movxf_internal}
     (expr_list:REG_EQUIV (const_double:XF

with "invalid" XFmode real again.  Here DSE1 does

 (note 3 0 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
-(note 2 3 5 2 NOTE_INSN_FUNCTION_BEG)
-(insn 5 2 6 2 (set (reg:V8HI 51 xmm15)
-        (mem/u/c:V8HI (symbol_ref/u:DI ("*.LC0") [flags 0x2]) [0  S16 A128]))
"t.c":8:15 1694 {movv8hi_internal}
-     (expr_list:REG_EQUAL (const_vector:V8HI [
-                (const_int 512 [0x200])
-                (const_int 0 [0]) repeated x3
-                (const_int 16384 [0x4000])
-                (const_int 0 [0]) repeated x3
-            ])
-        (nil)))
-(insn 6 5 7 2 (set (mem/c:V8HI (plus:DI (reg/f:DI 19 frame)
-                (const_int -16 [0xfffffffffffffff0])) [2  S16 A128])
-        (reg:V8HI 51 xmm15)) "t.c":8:15 1694 {movv8hi_internal}
-     (expr_list:REG_DEAD (reg:V8HI 51 xmm15)
-        (nil)))
-(insn 7 6 8 2 (set (reg:XF 86 [ t1 ])
-        (mem/c:XF (symbol_ref:DI ("t1") [flags 0x2]  <var_decl 0x7ffff6526bd0
t1>) [1 t1+0 S16 A128])) "t.c":9:6 140 {*movxf_internal}
-     (nil))

to

+(note 2 3 13 2 NOTE_INSN_FUNCTION_BEG)
+(insn 13 2 7 2 (set (reg:XF 88)
+        (mem/u/c:XF (symbol_ref/u:DI ("*.LC1") [flags 0x2]) [0  S16 A128]))
"t.c":8:15 140 {*movxf_internal}
+     (expr_list:REG_EQUAL (const_double:XF

so the issue needs to be mitigated in multiple places.  Even if we sanitize
the FP value we'd need to fix the DSE side which invokes
native_decode_rtx which seems to also lack the COMPOSITE_MODE handling.

But I do wonder whether real_from_target needs fixing to handle invalid
input gracefully which is ultimatively decode_ieee_extended?

Any opinions here?