register int *reg __asm__("%edi"); int test () { return *--reg <= 0; }
With -O2 -fomit-frame-pointer, 4.0, movl %edi, %eax leal -4(%edi), %edi movl -4(%eax), %eax testl %eax, %eax With 3.4, subl $4, %edi cmpl $0, (%edi) The problem appears to begin at the tree level, with extra temporaries: reg.0 = reg; reg.2 = reg.0 - 4B; reg = reg.2; return *reg.2 <= 0; We do consider hard register variables not is_gimple_reg, due to needing to V_MAY_DEF them at call sites. It would be nice if we could eliminate these temporaries during TER, or something. -- Summary: [4.0/4.1 Regression] extra temporaries when using global register variables Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: tree-optimization AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: rth at gcc dot gnu dot org CC: amacleod at redhat dot com,gcc-bugs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21596