[LLVMdev] GVN Infinite loop

[Chris Lattner]

On May 3, 2011, at 3:25 PM, Arushi Aggarwal wrote:

> Hi,
> 
> GVN seems to be running in an infinite loop on my example. I have attached the output of one iteration. I cant seem to reduce the testcase either. 
> 
> Any pointers to how to reduce the test case.

Bugzilla can reduce testcases that cause infinite loops (it has a -timeout flag), I'd try it.  Even if this doesn't help, please do file a bug with whatever you have.  This is likely to be a recent regression.

-Chris

> 
> THanks,
> Arushi
> 
> GVN iteration: 8
> GVN WIDENED LOAD:   %0 = load i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23), align 2, !dbg !875
> TO:   %1 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> GVN COERCED INST:
>   %0 = load i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23), align 2, !dbg !875
>   %1 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
>   %3 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> 
> 
> GVN removed:   %3 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> GVN WIDENED LOAD:   %0 = load i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23), align 2, !dbg !875
> TO:   %1 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> GVN COERCED INST:
>   %0 = load i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23), align 2, !dbg !875
>   %1 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
>   %6 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> 
> 
> GVN removed:   %6 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> GVN WIDENED LOAD:   %0 = load i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23), align 2, !dbg !875
> TO:   %1 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> GVN COERCED INST:
>   %0 = load i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23), align 2, !dbg !875
>   %1 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
>   %9 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> 
> 
> GVN removed:   %9 = load i16* bitcast (i8* getelementptr inbounds (%struct.CHESS_POSITION* @search, i64 0, i32 23) to i16*), align 2
> GVN removed:   %10 = trunc i16 %1 to i8
> GVN removed:   %10 = trunc i16 %3 to i8
> GVN removed:   %10 = trunc i16 %5 to i8
> GVN iteration: 9
> 
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