------- Comment #10 from thutt at vmware dot com 2009-01-22 13:59 ------- (In reply to comment #7) > The problem here is that you are using unitialized local register variables so > the register allocator does not know any better. Anyways it works correctly > on > the trunk and I don't have any other compiler to test with really (this is > both > with and without IRA). >
First, what's the expansion of the TLA 'IRA'? Second, it makes no difference if all the locals are initialized, the compiler still incorrectly uses '%rbp'. Here is the disassembly of the source, with initializers for all local variables. 0000000000000010 <test_function>: 10: 48 89 5c 24 d0 mov %rbx,0xffffffffffffffd0(%rsp) 15: 48 89 6c 24 d8 mov %rbp,0xffffffffffffffd8(%rsp) 1a: 31 db xor %ebx,%ebx 1c: 4c 89 64 24 e0 mov %r12,0xffffffffffffffe0(%rsp) 21: 4c 89 6c 24 e8 mov %r13,0xffffffffffffffe8(%rsp) 26: 31 c9 xor %ecx,%ecx 28: 4c 89 74 24 f0 mov %r14,0xfffffffffffffff0(%rsp) 2d: 4c 89 7c 24 f8 mov %r15,0xfffffffffffffff8(%rsp) 32: 31 d2 xor %edx,%edx 34: 48 83 ec 38 sub $0x38,%rsp 38: 31 f6 xor %esi,%esi 3a: 48 8b 2d 00 00 00 00 mov 0(%rip),%rbp # 41 <test_function+0x31> 41: 48 8b 05 00 00 00 00 mov 0(%rip),%rax # 48 <test_function+0x38> 48: 31 ed xor %ebp,%ebp 4a: 31 ff xor %edi,%edi 4c: 45 31 c0 xor %r8d,%r8d 4f: 45 31 c9 xor %r9d,%r9d 52: 45 31 d2 xor %r10d,%r10d 55: 45 31 db xor %r11d,%r11d 58: 45 31 e4 xor %r12d,%r12d 5b: 45 31 ed xor %r13d,%r13d 5e: 45 31 f6 xor %r14d,%r14d 61: 45 31 ff xor %r15d,%r15d 64: 0f 01 d8 vmrun 67: 48 8b 3d 00 00 00 00 mov 0(%rip),%rdi # 6e <test_function+0x5e> 6e: 48 8d 75 f8 lea 0xfffffffffffffff8(%rbp),%rsi 72: 48 39 fe cmp %rdi,%rsi 75: 74 05 je 7c <test_function+0x6c> 77: e8 00 00 00 00 callq 7c <test_function+0x6c> 7c: 48 8b 5c 24 08 mov 0x8(%rsp),%rbx 81: 48 8b 6c 24 10 mov 0x10(%rsp),%rbp 86: 31 c0 xor %eax,%eax 88: 4c 8b 64 24 18 mov 0x18(%rsp),%r12 8d: 4c 8b 6c 24 20 mov 0x20(%rsp),%r13 92: 4c 8b 74 24 28 mov 0x28(%rsp),%r14 97: 4c 8b 7c 24 30 mov 0x30(%rsp),%r15 9c: 48 83 c4 38 add $0x38,%rsp a0: c3 retq Third, why does removing the unused function 'SetupVMCB' cause the compiler to generate different code? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38925
