http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47581
Summary: [4.6 regression] Unnecessary adjustments to stack pointer Product: gcc Version: 4.6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization AssignedTo: unassig...@gcc.gnu.org ReportedBy: tony.popple...@gmail.com Whilst investigating PR4079 (which affects PPC), I found some strange adjustments to the stack pointer when compiling with 4.6.0 (20110129) on x86. For reference, the C code from that PR is: unsigned mulh(unsigned a, unsigned b) { return ((unsigned long long)a * (unsigned long long)b) >> 32; } On 4.5.2 using "-O2 -m32 -fomit-frame-pointer", this produced the following succinct code: mulh: movl 8(%esp), %eax mull 4(%esp) movl %edx, %eax ret .size mulh, .-mulh .ident "GCC: (GNU) 4.5.2" However on 4.6.0 with the same arguments: mulh: .LFB0: .cfi_startproc subl $4, %esp <== isn't this unnecessary? .cfi_def_cfa_offset 8 movl 12(%esp), %eax <== this could just be 8(%esp) mull 8(%esp) <== this could just be 4(%esp) addl $4, %esp <== isn't this unnecessary? .cfi_def_cfa_offset 4 movl %edx, %eax ret .cfi_endproc .LFE0: .size mulh, .-mulh .ident "GCC: (GNU) 4.6.0 20110129 (experimental)"