[LLVMbugs] [Bug 1069] NEW: Incorrect Post-Dominance Frontier Calculation

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Tue Dec 26 13:42:33 PST 2006


           Summary: Incorrect Post-Dominance Frontier Calculation
           Product: libraries
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Core LLVM classes
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: lefever at crhc.uiuc.edu

To the best of my knowledge, I have come across a bug in the post-dominance
frontier computation in LLVM.  In particular, LLVM computes the following
post-dominance frontier for the function at the end of this message:

Basic Block    Post-Dominance-Frontier
-----------    -----------------------
entry          -
bb             -
cond_next8     cond_next
cond_next12    cond_next
cond_next      -
bb21           cond_next8, cond_next12
cond_true27    cond_next8, cond_next12
pop.exit       cond_next8, cond_next12
cond_true.i    cond_true27
return         ??? return was not even listed in LLVM's PDF.

However, I believe the post-dominance frontier should be computed as such:

Basic Block    Post-Dominance-Frontier
-----------    -----------------------
entry          -
cond_next      entry
cond_next8     cond_next
cond_next12    cond_next8
bb21           cond_next8, cond_next12
cond_true27    bb21
cond_true.i    cond_true27
pop.exit       bb21
bb             cond_next, cond_next12
return         entry, bb21

Below is the function.
void %load_array(int %var_name) {
        %tmp = call sbyte %check_stack( int 1 )         ; <sbyte> [#uses=1]
        %tmp = seteq sbyte %tmp, 0              ; <bool> [#uses=1]
        br bool %tmp, label %return, label %cond_next

cond_next:              ; preds = %entry
        %tmp = load %struct.bc_var** %ex_stack          ; <%struct.bc_var*>
        %tmp = getelementptr %struct.bc_var* %tmp, int 0, uint 0               
; <%struct.bc_struct**> [#uses=1]
        %tmp = load %struct.bc_struct** %tmp            ; <%struct.bc_struct*>
        %tmp = call int %bc_num2long( %struct.bc_struct* %tmp )         ; <int>
        %tmp2 = setlt int %tmp, 0               ; <bool> [#uses=1]
        %tmp6 = setgt int %tmp, 65535           ; <bool> [#uses=1]
        %bothcond = or bool %tmp2, %tmp6                ; <bool> [#uses=1]
        br bool %bothcond, label %bb, label %cond_next8

cond_next8:             ; preds = %cond_next
        %tmp10 = seteq int %tmp, 0              ; <bool> [#uses=1]
        br bool %tmp10, label %cond_next12, label %bb21

cond_next12:            ; preds = %cond_next8
        %tmp16 = call sbyte %bc_is_zero( %struct.bc_struct* %tmp )             
; <sbyte> [#uses=1]
        %tmp17 = seteq sbyte %tmp16, 0          ; <bool> [#uses=1]
        br bool %tmp17, label %bb, label %bb21

bb:             ; preds = %cond_next12, %cond_next
        %tmp = load sbyte*** %a_names           ; <sbyte**> [#uses=1]
        %tmp19 = getelementptr sbyte** %tmp, int %var_name              ;
<sbyte**> [#uses=1]
        %tmp = load sbyte** %tmp19              ; <sbyte*> [#uses=1]
        call void (sbyte*, ...)* %rt_error( sbyte* getelementptr ([34 x sbyte]*
%str, int 0, uint 0), sbyte* %tmp )
        ret void

bb21:           ; preds = %cond_next12, %cond_next8
        %tmp24 = call %struct.bc_struct** %get_array_num( int %var_name, int
%tmp )             ; <%struct.bc_struct**> [#uses=2]
        %tmp26 = seteq %struct.bc_struct** %tmp24, null         ; <bool> [#uses=1]
        br bool %tmp26, label %return, label %cond_true27

cond_true27:            ; preds = %bb21
        %tmp.i = load %struct.bc_var** %ex_stack                ;
<%struct.bc_var*> [#uses=4]
        %tmp.i = seteq %struct.bc_var* %tmp.i, null             ; <bool> [#uses=1]
        br bool %tmp.i, label %pop.exit, label %cond_true.i

cond_true.i:            ; preds = %cond_true27
        %tmp.i = getelementptr %struct.bc_var* %tmp.i, int 0, uint 1           
; <%struct.bc_var**> [#uses=1]
        %tmp3.i = load %struct.bc_var** %tmp.i          ; <%struct.bc_var*>
        store %struct.bc_var* %tmp3.i, %struct.bc_var** %ex_stack
        %tmp.i = getelementptr %struct.bc_var* %tmp.i, int 0, uint 0           
; <%struct.bc_struct**> [#uses=1]
        call void %bc_free_num( %struct.bc_struct** %tmp.i )
        %tmp5.i = bitcast %struct.bc_var* %tmp.i to sbyte*              ;
<sbyte*> [#uses=1]
        call void %free( sbyte* %tmp5.i )
        br label %pop.exit

pop.exit:               ; preds = %cond_true.i, %cond_true27
        %tmp29 = load %struct.bc_struct** %tmp24                ;
<%struct.bc_struct*> [#uses=1]
        call void %push_copy( %struct.bc_struct* %tmp29 )
        ret void

return:         ; preds = %bb21, %entry
        ret void



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