[Bug middle-end/52831] New: extract_bit_field_1: issue when str_rtx unsafe from target

[aurelien.buhrig.gcc at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52831

             Bug #: 52831
           Summary: extract_bit_field_1: issue when str_rtx unsafe from
                    target
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: aurelien.buhrig....@gmail.com


This bug makes gcc.c-torture/execute/20040625-1.c fail on my private target
port with gcc 4.6.3. Note that it also occurs on trunk during expand, but it
seems to be masked by next passes.

The issue occurs when:
- str_rtx (op0) is not safe from target
- when bitsize > BITS_PER_WORD

Example:

WORD_MODE = HImode
Pmode == ptr_mode == PSImode

extract_bit_field_1 (str_rtx=0x2aaaac15be28, bitsize=32, bitnum=0, unsignedp=1,
packedp=1 '\001', target=0x2aaaac16c880, mode=PSImode, tmode=PSImode, 
    fallback_p=1 '\001')
(gdb) call debug_rtx (str_rtx)
(mem:BLK (reg/v/f:PSI 22 [ s ]) [2 *s_3(D)+0 S4 A8])
(gdb) call debug_rtx (target)
(reg/v/f:PSI 22 [ s ])

Here is the expand log from trunk (see insns 19 and 20):

; s_4 = s_3(D)->next;

(insn 10 9 11 (clobber (reg/v/f:PSI 22 [ s ]))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 11 10 12 (set (reg:QI 25)
        (mem:QI (plus:PSI (reg/v/f:PSI 22 [ s ])
                (const_int 2 [0x2])) [0+2 S1 A8]))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 12 11 13 (set (reg:HI 24)
        (zero_extend:HI (reg:QI 25)))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 13 12 14 (set (reg:HI 26)
        (reg:HI 24))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 14 13 15 (set (reg:HI 26)
        (unspec:HI [
                (reg:HI 26)
            ] 11))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 15 14 16 (set (strict_low_part (subreg:QI (reg:HI 26) 1))
        (const_int 0 [0]))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 16 15 17 (set (reg:QI 28)
        (mem:QI (plus:PSI (reg/v/f:PSI 22 [ s ])
                (const_int 3 [0x3])) [0+3 S1 A8]))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 17 16 18 (set (reg:HI 27)
        (zero_extend:HI (reg:QI 28)))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 18 17 19 (set (reg:HI 29)
        (ior:HI (reg:HI 27)
            (reg:HI 26)))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 19 18 20 (set (subreg:HI (reg/v/f:PSI 22 [ s ]) 2)
        (reg:HI 29))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 20 19 21 (set (reg:QI 31)
        (mem:QI (reg/v/f:PSI 22 [ s ]) [0+0 S1 A8]))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 21 20 22 (set (reg:HI 30)
        (zero_extend:HI (reg:QI 31)))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))

(insn 22 21 23 (set (reg:HI 32)
        (reg:HI 30))
/home/buhrig/work/sdk/gcc/trunk/src/gcc/testsuite/gcc.c-torture/execute/20040625-1.c:8
-1
     (nil))


The provided patch solves the issue by using an intermediate reg, when needed,
before extracting in word mode.