In the following testcase, a read memory access should be made. However gcc -O2 optimizes away the code inside the test function.
------------------- test.c -------------------- void test (char *addr) { *((volatile char *) addr); } ----------------------------------------------- $ gcc -Wall -O2 -S test.c ------------------- test.s -------------------- test.s: .file "test.c" .text .p2align 4,,15 .globl test .type test, @function test: pushl %ebp movl %esp, %ebp popl %ebp ret .size test, .-test .ident "GCC: (GNU) 4.1.0 20050702 (experimental)" .section .note.GNU-stack,"",@progbits ----------------------------------------------- -- Summary: gcc -O2 discards cast to volatile Product: gcc Version: 4.1.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: olivier dot baudron at m4x dot org CC: gcc-bugs at gcc dot gnu dot org GCC host triplet: i686-pc-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22278