[LLVMbugs] [Bug 865] NEW: Coallescer is really confused or something

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=865

           Summary: Coallescer is really confused or something
           Product: libraries
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: sabre at nondot.org
                CC: natebegeman at mac.com


llc -fast -march=x86 on this .ll file:

int %foo(int* %a, int %t, int %C) {
entry:
        %a = cast int* %a to uint               ; <uint> [#uses=1]
        br label %cond_true

cond_true:              ; preds = %cond_true, %entry
        %iv. = phi uint [ %a, %entry ], [ %iv..inc, %cond_true ]                ; <uint> [#uses=2]
        %t_addr.0.0 = phi int [ %t, %entry ], [ %tmp7, %cond_true ]             ; <int> [#uses=2]
        %iv. = cast uint %iv. to int*           ; <int*> [#uses=1]
        %tmp3 = load int* %iv.          ; <int> [#uses=1]
        %tmp7 = add int %t_addr.0.0, %tmp3              ; <int> [#uses=1]
        %tmp = setgt int %C, 39         ; <bool> [#uses=1]
        %iv..inc = add uint %iv., 4             ; <uint> [#uses=1]
        br bool %tmp, label %bb12, label %cond_true

bb12:           ; preds = %cond_true
        ret int %t_addr.0.0
}

produces:

_foo:
        subl $4, %esp
        movl %esi, (%esp)
        movl 8(%esp), %ecx
        movl 16(%esp), %edx
        movl 12(%esp), %esi
LBB1_1: #cond_true
***     movl %esi, %eax
***     movl %eax, %esi
        addl (%ecx), %esi
        addl $4, %ecx
        cmpl $40, %edx
        jl LBB1_1       #cond_true
LBB1_2: #bb12
        movl (%esp), %esi
        addl $4, %esp
        ret

It is safe to say that that is not the fastest way to copy esi into esi.  Note that eax is dead.

-Chris



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