llvm-debug-info-blog

How to reduce a test case using LLVM bugpoint?

For example, the compilation of the huge-test.c crashes during the CodeGen/LiveDebugValues pass. Please find below the steps to reduce the bug.

Convert the test written in a highlevel language to LLVM Assembly

$ clang -g -O2 huge-test.c -S -emit-llvm

Confirm the bug still exists

$ llc -O2 huge-test.ll
... Assertion 'isTrue(...'
Stack dump:
0. Program arguments ...

Simplify the case

$ bugpoint -llc-safe huge-test.ll

Or additional arguments to the 'llc' tool could be passed as:

$ bugpoint -llc-safe -safe-tool-args -mtriple=ppc-linux-gnueabi huge-test.ll

If everything is OK, the 'bugpoint-reduced-simplified.bc' will be created.

Disassemble the output to create 'bugpoint-reduced-simplified.ll' file

$ llvm-dis bugpoint-reduced-simplified.bc

Confirm again the problem still exists

$ llc -O2 bugpoint-reduced-simplified.ll
... Assertion 'isTrue(...'
Stack dump:
0. Program arguments ...

Simplify the case furthermore

$ opt -S -strip-dead-prototypes --strip-nondebug bugpoint-reduced-simplified.ll > debug-info-bug-striped-case.ll

Confirm again the problem still exists

$ llc -O2 debug-info-bug-striped-case.ll
... Assertion 'isTrue(...'
Stack dump:
0. Program arguments ...