[LLVMbugs] [Bug 22110] New: while+switch at -O2 mixes up line info

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Jan 6 14:12:33 PST 2015


            Bug ID: 22110
           Summary: while+switch at -O2 mixes up line info
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: paul_robinson at playstation.sony.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13641
  --> http://llvm.org/bugs/attachment.cgi?id=13641&action=edit
Sample source

Compiling the attached source with -O2 -g (or -gline-tables-only) and
the line info for the head of the while loop gets pretty confused.
Two instructions basically have their line info swapped, and another
instruction at the top of a block has no info at all.

The relevant source fragment is this (pData is a char*, Op is an enum):
/*25*/  while (1) {
/*26*/    Op op = static_cast<Op>(*pData++);
/*27*/    switch (op) {

which for me generated the following... note that
.LBB0_8 is one case of the switch, which was laid out above the
top of the loop--that's fine--but the line info clearly isn't right.
I added some annotations to help point out the problem.

## This is the case from the switch, which is fine.
.LBB0_8:                                # %if.then
                                        #   in Loop: Header=BB0_1 Depth=1
        .loc    1 47 11 prologue_end    # bz92041.cpp:47:11
        movswq  1(%rsi), %rcx
        leaq    3(%rcx,%rsi), %rdi
.LBB0_1:                                # %while.body
                                        # =>This Inner Loop Header: Depth=1
## NO LINE INFO HERE--1st instr of loop body inherits from prior basic block
        movq    %rdi, %rsi
## WRONG LINE INFO HERE--Load of *pData has line info for switch()
        .loc    1 27 5                  # bz92041.cpp:27:5
        movzbl  (%rsi), %ecx
## WRONG LINE INFO HERE--Range-check has line info for the load
        .loc    1 26 29                 # bz92041.cpp:26:29
        cmpq    $3, %rcx
        .loc    1 27 5                  # bz92041.cpp:27:5
        ja      .LBB0_9
# BB#2:                                 # %while.body
                                        #   in Loop: Header=BB0_1 Depth=1
## Post-increment (*pData++) has correct line info
        .loc    1 26 30                 # bz92041.cpp:26:30
        leaq    1(%rsi), %rdi
## WRONG LINE INFO HERE--switch dispatch inherits from previous instr
        jmpq    *.LJTI0_0(,%rcx,8)

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