GCC Middle and Back End API Reference
init-regs.c File Reference


static void initialize_uninitialized_regs ()
static bool gate_initialize_regs ()
static unsigned int rest_of_handle_initialize_regs ()
rtl_opt_passmake_pass_initialize_regs ()

Function Documentation

static bool gate_initialize_regs ( )
static void initialize_uninitialized_regs ( )

Initialization of uninitialized regs. Copyright (C) 2007-2013 Free Software Foundation, Inc.

This file is part of GCC.

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   Check all of the uses of pseudo variables.  If any use that is MUST
   uninitialized, add a store of 0 immediately before it.  For
   subregs, this makes combine happy.  For full word regs, this makes
   other optimizations, like the register allocator and the reg-stack
   happy as well as papers over some problems on the arm and other
   processors where certain isa constraints cannot be handled by gcc.
   These are of the form where two operands to an insn my not be the
   same.  The ra will only make them the same if they do not
   interfere, and this can only happen if one is not initialized.

   There is also the unfortunate consequence that this may mask some
   buggy programs where people forget to initialize stack variable.
   Any programmer with half a brain would look at the uninitialized
   variable warnings.  
                 Only do this for the pseudos.  
                 Do not generate multiple moves for the same regno.
                 This is common for sequences of subreg operations.
                 They would be deleted during combine but there is no
                 reason to churn the system.  
                 A use is MUST uninitialized if it reaches the top of
                 the block from the inside of the block (the lr test)
                 and no def for it reaches the top of the block from
                 outside of the block (the ur test).  

Referenced by gate_initialize_regs().

rtl_opt_pass* make_pass_initialize_regs ( )
static unsigned int rest_of_handle_initialize_regs ( )