[LLVMdev] a LICM bug (in LLVM-2.7)?

[Chuck Zhao]

  I am studying the Transform/Scalar/LICM.cpp pass, and wrote a simple 
test program to validate.

void testLICM(void){
   int i,N=100;
   int data;
   for(i=0;i<N;i++){
     data = 1;
     printf("i: %d\n",i);
   }
   printf("data: %d\n", data);
}


I expect the "data=1" will be moved out of loop (either hoist or sink).
However, to my surprise, that statement remains within the loop after -licm.

This is the licm produced IR:

define void @testLICM() nounwind {
entry:
   %i = alloca i32                                 ; <i32*> [#uses=3]
   %N = alloca i32                                 ; <i32*> [#uses=2]
   %data = alloca i32                              ; <i32*> [#uses=2]
   %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
   call void @llvm.dbg.declare(metadata !{i32* %i}, metadata !0), !dbg !7
   call void @llvm.dbg.declare(metadata !{i32* %N}, metadata !8), !dbg !7
   call void @llvm.dbg.declare(metadata !{i32* %data}, metadata !9), !dbg !7
   store i32 100, i32* %N, align 4, !dbg !10
   store i32 0, i32* %i, align 4, !dbg !11
   %0 = load i32* %N, align 4, !dbg !11            ; <i32> [#uses=1]
   %i.promoted = load i32* %i                      ; <i32> [#uses=1]
   br label %bb1, !dbg !11

bb:                                               ; preds = %bb1
   store i32 1, i32* %data, align 4, !dbg !12
   %1 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr inbounds 
([7 x i8]* @.str, i32 0, i32 0), i32 %i.tmp.0) nounwind, !dbg !13 ; 
<i32> [#uses=0]
   %2 = add nsw i32 %i.tmp.0, 1, !dbg !11          ; <i32> [#uses=1]
   br label %bb1, !dbg !11

bb1:                                              ; preds = %bb, %entry
   %i.tmp.0 = phi i32 [ %i.promoted, %entry ], [ %2, %bb ] ; <i32> [#uses=4]
   %3 = icmp slt i32 %i.tmp.0, %0, !dbg !11        ; <i1> [#uses=1]
   br i1 %3, label %bb, label %bb2, !dbg !11

bb2:                                              ; preds = %bb1
   store i32 %i.tmp.0, i32* %i
   %4 = load i32* %data, align 4, !dbg !14         ; <i32> [#uses=1]
   %5 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr inbounds 
([10 x i8]* @.str1, i32 0, i32 0), i32 %4) nounwind, !dbg !14 ; <i32> 
[#uses=0]
   br label %return, !dbg !15

return:                                           ; preds = %bb2
   ret void, !dbg !15
}


I ran the program with licm only option through opt:
opt -licm < test.bc > test.licm.bc


Is this a bug, or am I running it in a wrong way?

Thank you

Chuck

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