[Bug rtl-optimization/63548] New: redundent reload in loop after removing regmove

[wmi at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63548

            Bug ID: 63548
           Summary: redundent reload in loop after removing regmove
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wmi at google dot com

Created attachment 33730
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33730&action=edit
testcase 1.c

For program with many insns like "a = b + c", where operands "b" and "c" are
both dead immediately after the add insn, the hardreg preference heuristic
seems not perfect.

Here is a testcase 1.c,

For gcc after r204212, they generates two redundent reload insns caused by
imperfect hardreg preference heuristic in IRA. 

~/workarea/gcc-r214579/build/install/bin/gcc -O2 -S 1.c

.L5:
        movl    %ebx, %edi
        call    goo
        leal    2(%rbx), %edi
        movl    %eax, %r13d
        call    goo
        leal    4(%rbx), %edi
        movl    %eax, %r12d
        call    goo
        leal    6(%rbx), %edi
        movl    %eax, %ebp
        addl    $1, %ebx
        call    goo
        movl    %eax, %edx         // redundent mov
        movl    %r13d, %eax        // redundent mov
        imull   %r12d, %eax
        imull   %ebp, %eax
        imull   %edx, %eax
        addl    %eax, total(%rip)
        cmpl    %ebx, M(%rip)
        jg      .L5

For old gcc with regmove, it happens to be better than hardreg preference
heuristic and generates one redundent reload.

~/workarea/gcc-r199418/build/install/bin/gcc -O2 -S 1.c
.L3:
        movl    %ebx, %edi
        call    goo
        leal    2(%rbx), %edi
        movl    %eax, %r13d
        call    goo
        leal    4(%rbx), %edi
        movl    %eax, %r12d
        call    goo
        leal    6(%rbx), %edi
        movl    %eax, %ebp
        addl    $1, %ebx
        call    goo
        movl    %r13d, %edx        // redundent mov
        imull   %r12d, %edx
        imull   %ebp, %edx
        imull   %eax, %edx
        addl    %edx, total(%rip)
        cmpl    %ebx, M(%rip)
        jg      .L3

llvm generates no redundent move insn.

clang-r217862 -O2 -S 1.c
.LBB0_2:                       
        movl    %ebx, %edi
        callq   goo
        movl    %eax, %r14d
        leal    2(%rbx), %edi
        callq   goo
        movl    %eax, %ebp
        leal    4(%rbx), %edi
        callq   goo
        movl    %eax, %r15d
        leal    6(%rbx), %edi
        callq   goo
        imull   %r14d, %ebp
        imull   %r15d, %ebp
        imull   %eax, %ebp
        addl    %ebp, total(%rip)
        incl    %ebx
        cmpl    M(%rip), %ebx
        jl      .LBB0_2