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[Bug middle-end/53823] [4.8 Regression] FAIL: gcc.c-torture/execute/930921-1.c execution at -O0 and -O1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53823

--- Comment #14 from dave.anglin at bell dot net 2012-07-31 22:54:59 UTC ---
On 31-Jul-12, at 5:29 PM, rth at gcc dot gnu.org wrote:

> How does this -O1 output compare with native?


There seems to an off by one error in various shifts, etc.   For  
example,

;(insn 8 4 10 (set (reg:SI 19 %r19 [104])
;        (lshiftrt:SI (reg:SI 24 %r24 [orig:100 y+4 ] [100])
;            (const_int 27 [0x1b]))) xxx.c:5 179 {lshrsi3}
;     (nil))
         extru %r24,4,5,%r19     ; 8     lshrsi3/2       [length = 4]

With 4.6, I see something similar to what you see:

;(insn 8 62 10 (set (reg:SI 20 %r20 [104])
;        (lshiftrt:SI (reg:SI 24 %r24 [orig:136+4 ] [136])
;            (const_int 28 [0x1c]))) xxx.c:5 178 {lshrsi3}
;     (nil))
         extru %r24,3,4,%r20     ; 8     lshrsi3/2       [length = 4]

--
John David Anglin    dave.anglin@bell.net


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