[llvm-bugs] [Bug 34827] New: Csmith program prints checksum at -O0, but crashes at -O1
llvm-bugs at lists.llvm.org
Tue Oct 3 23:02:23 PDT 2017
Bug ID: 34827
Summary: Csmith program prints checksum at -O0, but crashes at
Component: Common Code Generator Code
Assignee: unassignedbugs at nondot.org
Reporter: paulsson at linux.vnet.ibm.com
CC: llvm-bugs at lists.llvm.org
Created attachment 19228
Csmith generated a program that when built and executed at -O0 gives completely
different behaviour as when the same is done with -O1:
bin/clang -O0 -march=z13 tc_O1IllegalIns.ll -o a.out
checksum = F8458AC2
bin/clang -O1 -march=z13 tc_O1IllegalIns.ll -o a.out
Illegal instruction (core dumped)
>From what I am seeing, the Trap instruction is generated at -O1, but not at
-O0, and my best guess is that this difference is the reason for the crash with
tc_O1IllegalIns.ll is the reduced input that has apparently the same behaviour
as the original csmith program.
Is this expected for some reason, or should this be fixed per the rule that
optimization levels should not affect the program result?
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