[LLVMbugs] [Bug 19261] New: unconditional branch is not generated with -O0 -fast-isel=false

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu Mar 27 07:54:49 PDT 2014


            Bug ID: 19261
           Summary: unconditional branch is not generated with -O0
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: daniil.fukalov at amd.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 12301
  --> http://llvm.org/bugs/attachment.cgi?id=12301&action=edit
input for llc

llc doesn't generate nodes for unconditional fall-through branches for targets
without FastISel implementation (X86 has it, but can be disabled by
"-fast-isel=false") SelectionDAGBuilder::visitBr().
So for line 4 in the following testcase

1: void foo(int i){
2:   switch(i){
3:   default:
4:     break;
5:   }
6:   return;
7: }

there is no corresponding line in .debug_line section, and a debugger cannot
set a breakpoint at line 4.

The test.ll IR file is attached (generated with clang -g -O0).

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