Interaction

$ clang++ -O1 -g test.cc  -fno-omit-frame-pointer -o test && ~/src/chromium/src/third_party/valgrind/linux_x64/bin/valgrind ./test
==10069== Memcheck, a memory error detector
==10069== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==10069== Using Valgrind-3.9.0.SVN and LibVEX; rerun with -h for copyright info
==10069== Command: ./test
==10069== 
==10069== Conditional jump or move depends on uninitialised value(s)
==10069==    at 0x400597: main (test.cc:15)
==10069== 
Yep.
==10069== 
==10069== HEAP SUMMARY:
==10069==     in use at exit: 0 bytes in 0 blocks
==10069==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==10069== 
==10069== All heap blocks were freed -- no leaks are possible
==10069== 
==10069== For counts of detected and suppressed errors, rerun with: -v
==10069== Use --track-origins=yes to see where uninitialised values come from
==10069== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)

test.cc

#include <stdio.h>

__attribute__((noinline)) bool InitializeIf(volatile bool cond, int* var) {
  if (!cond)
    return false;

  *var = 3;
  return true;
}


int main() {
  int var;
  bool initted = InitializeIf(false, &var);
  if (!initted || var == 2)
    printf("Yep.\n");
}

test.s

        .file   "test.cc"
        .text
        .globl  _Z12InitializeIfbPi
        .align  16, 0x90
        .type   _Z12InitializeIfbPi,@function
_Z12InitializeIfbPi:                    # @_Z12InitializeIfbPi
        .cfi_startproc                  
# BB#0:                                 # %entry
        movb    %dil, -1(%rsp)          
        testb   $1, -1(%rsp)
        je      .LBB0_1
# BB#2:                                 # %if.end
        movl    $3, (%rsi)              
        movb    $1, %al
                                        # kill: AL<def> AL<kill> EAX<kill>
        ret                             
.LBB0_1:
        xorl    %eax, %eax
                                        # kill: AL<def> AL<kill> EAX<kill>
        ret
.Ltmp0: 
        .size   _Z12InitializeIfbPi, .Ltmp0-_Z12InitializeIfbPi
        .cfi_endproc

        .globl  main
        .align  16, 0x90
        .type   main,@function
main:                                   # @main
        .cfi_startproc
# BB#0:                                 # %entry
        pushq   %rbp
.Ltmp3: 
        .cfi_def_cfa_offset 16
.Ltmp4: 
        .cfi_offset %rbp, -16
        movq    %rsp, %rbp
.Ltmp5: 
        .cfi_def_cfa_register %rbp
        subq    $16, %rsp
        leaq    -4(%rbp), %rsi
        xorl    %edi, %edi
        callq   _Z12InitializeIfbPi
        cmpl    $2, -4(%rbp)
        je      .LBB1_2
# BB#1:                                 # %entry
        xorb    $1, %al
        je      .LBB1_3
.LBB1_2:                                # %if.then
        movl    $.Lstr, %edi
        callq   puts
.LBB1_3:                                # %if.end
        xorl    %eax, %eax
        addq    $16, %rsp
        popq    %rbp
        ret
.Ltmp6: 
        .size   main, .Ltmp6-main
        .cfi_endproc

        .type   .L.str,@object          # @.str
        .section        .rodata.str1.1,"aMS",@progbits,1
.L.str: 
        .asciz  "Yep.\n"
        .size   .L.str, 6

        .type   .Lstr,@object           # @str
.Lstr:  
        .asciz  "Yep."
        .size   .Lstr, 5


        .section        ".note.GNU-stack","",@progbits