GVN Infinite loop

Project Infrastructure LLVM Dev List Archives
1

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.

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
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
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
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

2

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.

Are you running with LLVM 2.9 or LLVM mainline?

– John T.

3

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

4

That trick worked. Filed as bug 9841.

Thanks,
Arushi