[Bug target/39386] [avr] different computation results for O1 and O0 executables

[anitha dot boyapati at atmel dot com]

------- Comment #8 from anitha dot boyapati at atmel dot com  2010-08-23 13:25 -------
When -O2 is enabled result is 0xFF (255) which is incorrect. The code generated
for the following shift operation:

13:              return  (left << right);
+000000AB:   C004        RJMP      PC+0x0005      Relative jump
+000000AC:   0F22        LSL       R18            Logical Shift Left
+000000AD:   1F33        ROL       R19            Rotate Left Through Carry
+000000AE:   1F44        ROL       R20            Rotate Left Through Carry
+000000AF:   1F55        ROL       R21            Rotate Left Through Carry
+000000B0:   952A        DEC       R18            Decrement
+000000B1:   F7D2        BRPL      PC-0x05        Branch if plus
19:          g_6= func_1 (g_6, g_6);
+000000B2:   93200100    STS       0x0100,R18     Store direct to data space

'left' is stored in registers R21:R20:R19:R18 as it is typecasted to uint32_t
type while 'right' is stored in R18. Because of shift logic, R18 becomes 0xFF
in first iteration which is then stored.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39386