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From: dp@fc.hp.com To: gcc-gnats@gcc.gnu.org Subject: optimization/6064: byte swap function returns bad value Date: Tue, 26 Mar 2002 08:16:00 -0000 [thread overview] Message-ID: <20020326161500.592.qmail@sources.redhat.com> (raw) >Number: 6064 >Category: optimization >Synopsis: byte swap function returns bad value >Confidential: no >Severity: serious >Priority: medium >Responsible: unassigned >State: open >Class: sw-bug >Submitter-Id: net >Arrival-Date: Tue Mar 26 08:16:01 PST 2002 >Closed-Date: >Last-Modified: >Originator: David Pinedo >Release: gcc-2.96-85 >Organization: >Environment: Red Hat Linux 7.1 plus some errata gcc rpm is 2.96-85 Pentium III processor >Description: Compile and run the following program: unsigned int byteSwap(unsigned int * word) { char* byte; unsigned int *uip; char newWord[4]; byte = (char*) word; newWord[3] = *byte++; newWord[2] = *byte++; newWord[1] = *byte++; newWord[0] = *byte++; uip = (unsigned int*)newWord; return *uip; } main(int argc, char **argv) { unsigned int ui; ui=0x11223344; printf("%08x\n", byteSwap(&ui)); } If -O2 optimization is used, the output is: 4433f894 (incorrect) If -O1 optimization is used, the output is: 44332211 (correct) With -O2 optimization, if the variable newWord is declared static, the output is correct. >How-To-Repeat: >Fix: >Release-Note: >Audit-Trail: >Unformatted:
next reply other threads:[~2002-03-26 16:16 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-03-26 8:16 dp [this message] 2002-04-03 2:41 rth
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