[LLVMbugs] [Bug 10858] New: Optimizer removes call to relevant function

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=10858

           Summary: Optimizer removes call to relevant function
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: dwelch at dwelch.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=7219)
 --> (http://llvm.org/bugs/attachment.cgi?id=7219)
simple source files needed to reproduce this problem

See attached.

show.c has a function get_onechar that calls uart_getc().  uart_getc() for
debugging includes an infinite loop.  the call to uart_getc() appears to be
optimized completely out and the code continues as if it had never happened.

00000000 <get_onechar>:
   0:    b510          push    {r4, lr}
   2:    4604          mov    r4, r0
   4:    20ff          movs    r0, #255    ; 0xff
   6:    4020          ands    r0, r4
   8:    280a          cmp    r0, #10

Interestingly I added a function called fun() which also calls uart_getc() and
this one appears to have been implemented with a call to uart_putc()

00000022 <fun>:
  22:    b500          push    {lr}
  24:    4601          mov    r1, r0
  26:    2007          movs    r0, #7
  28:    0740          lsls    r0, r0, #29
  2a:    f7ff fffe     bl    0 <PUT32>
  2e:    bd00          pop    {pc}


Without optimization everything looks fine.

Tried with both a near trunk (will svn up and try again today) as well as
release 2.9

Dont actually need to assemble and disassemble with binutils as the Makefile
does, the problem can be seen in the .s file.

running ubuntu 10.4LTS 64 bit 

Linux dwelch-desktop 2.6.32-33-generic #72-Ubuntu SMP Fri Jul 29 21:07:13 UTC
2011 x86_64 GNU/Linux

Low Level Virtual Machine (http://llvm.org/):
  llvm version 3.0svn
  Optimized build with assertions.
  Built Aug 31 2011 (22:39:17).
  Host: x86_64-unknown-linux-gnu
  Host CPU: amdfam10

llvm# svn info
Path: .
URL: http://llvm.org/svn/llvm-project/llvm/trunk
Repository Root: http://llvm.org/svn/llvm-project
Repository UUID: 91177308-0d34-0410-b5e6-96231b3b80d8
Revision: 138935
Node Kind: directory
Schedule: normal
Last Changed Author: evancheng
Last Changed Rev: 138934
Last Changed Date: 2011-08-31 21:45:00 -0400 (Wed, 31 Aug 2011)

llvm/tools/clang# svn info
Path: .
URL: http://llvm.org/svn/llvm-project/cfe/trunk
Repository Root: http://llvm.org/svn/llvm-project
Repository UUID: 91177308-0d34-0410-b5e6-96231b3b80d8
Revision: 138935
Node Kind: directory
Schedule: normal
Last Changed Author: dgregor
Last Changed Rev: 138935
Last Changed Date: 2011-08-31 22:09:07 -0400 (Wed, 31 Aug 2011)

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