The contents of the note is the insn that stored the 0.   If that insn is deleted or patched to a NOTE, the REG_WAS_0 is inoperative.   The REG_WAS_0 note is actually an INSN_LIST, not an EXPR_LIST.     REG_NONNEG means that the register is always nonnegative during   the containing loop.  This is used in branches so that decrement and   branch instructions terminating on zero can be matched.     REG_UNSET identifies a pseudo-reg used in this insn and never set.  */#define REG_NOTES(INSN)	((INSN)->fld[6].rtx)/* Don't forget to change reg_note_name in rtl.c.  */enum reg_note { REG_DEAD = 1, REG_INC = 2, REG_EQUIV = 3, REG_WAS_0 = 4,		REG_EQUAL = 5, REG_RETVAL = 6, REG_LIBCALL = 7,		REG_NONNEG = 8, REG_UNSET = 9 };/* Extract the reg-note kind from an EXPR_LIST.  */#define REG_NOTE_KIND(LINK) ((enum reg_note) GET_MODE (LINK))/* Names for REG_NOTE's in EXPR_LIST insn's.  */extern char *reg_note_name[];#define GET_REG_NOTE_NAME(MODE) (reg_note_name[(int)(MODE)])/* The label-number of a code-label.  The assembler label   is made from `L' and the label-number printed in decimal.   Label numbers are unique in a compilation.  */#define CODE_LABEL_NUMBER(INSN)	((INSN)->fld[3].rtint)#define LINE_NUMBER NOTE/* In a NOTE that is a line number, this is a string for the file name   that the line is in.  */#define NOTE_SOURCE_FILE(INSN)  ((INSN)->fld[3].rtstr)/* In a NOTE that is a line number, this is the line number.   Other kinds of NOTEs are identified by negative numbers here.  */#define NOTE_LINE_NUMBER(INSN) ((INSN)->fld[4].rtint)/* Codes that appear in the NOTE_LINE_NUMBER field   for kinds of notes that are not line numbers.  *//* This note indicates the end of the real body of the function,   after moving the parms into their homes, etc.  */#define NOTE_INSN_FUNCTION_BEG 0/* This note is used to get rid of an insn   when it isn't safe to patch the insn out of the chain.  */#define NOTE_INSN_DELETED -1#define NOTE_INSN_BLOCK_BEG -2#define NOTE_INSN_BLOCK_END -3#define NOTE_INSN_LOOP_BEG -4#define NOTE_INSN_LOOP_END -5/* This kind of note is generated at the end of the function body,   just before the return insn or return label.   In an optimizing compilation it is deleted by the first jump optimization,   after enabling that optimizer to determine whether control can fall   off the end of the function body without a return statement.  */#define NOTE_INSN_FUNCTION_END -6/* This kind of note is generated just after each call to `setjmp', et al.  */#define NOTE_INSN_SETJMP -7/* Generated at the place in a loop that `continue' jumps to.  */#define NOTE_INSN_LOOP_CONT -8/* Don't forget to change note_insn_name in rtl.c.  */#define NOTE_DECL_NAME(INSN) ((INSN)->fld[3].rtstr)#define NOTE_DECL_CODE(INSN) ((INSN)->fld[4].rtint)#define NOTE_DECL_RTL(INSN) ((INSN)->fld[5].rtx)#define NOTE_DECL_IDENTIFIER(INSN) ((INSN)->fld[6].rtint)#define NOTE_DECL_TYPE(INSN) ((INSN)->fld[7].rtint)/* Names for NOTE insn's other than line numbers.  */extern char *note_insn_name[];#define GET_NOTE_INSN_NAME(NOTE_CODE) (note_insn_name[-(NOTE_CODE)])/* In jump.c, each label contains a count of the number   of LABEL_REFs that point at it, so unused labels can be deleted.  */#define LABEL_NUSES(LABEL) ((LABEL)->fld[4].rtint)/* In jump.c, each JUMP_INSN can point to a label that it can jump to,   so that if the JUMP_INSN is deleted, the label's LABEL_NUSES can   be decremented and possibly the label can be deleted.  */#define JUMP_LABEL(INSN)   ((INSN)->fld[7].rtx)/* Once basic blocks are found in flow.c,   each CODE_LABEL starts a chain that goes through   all the LABEL_REFs that jump to that label.   The chain eventually winds up at the CODE_LABEL; it is circular.  */#define LABEL_REFS(LABEL) ((LABEL)->fld[4].rtx)/* This is the field in the LABEL_REF through which the circular chain   of references to a particular label is linked.   This chain is set up in flow.c.  */#define LABEL_NEXTREF(REF) ((REF)->fld[1].rtx)/* Once basic blocks are found in flow.c,   Each LABEL_REF points to its containing instruction with this field.  */#define CONTAINING_INSN(RTX) ((RTX)->fld[2].rtx)/* For a REG rtx, REGNO extracts the register number.  */#define REGNO(RTX) ((RTX)->fld[0].rtint)/* For a REG rtx, REG_FUNCTION_VALUE_P is nonzero if the reg   is the current function's return value.  */#define REG_FUNCTION_VALUE_P(RTX) ((RTX)->integrated)/* 1 in a REG rtx if it corresponds to a variable declared by the user.  */#define REG_USERVAR_P(RTX) ((RTX)->volatil)/* For a CONST_INT rtx, INTVAL extracts the integer.  */#define INTVAL(RTX) ((RTX)->fld[0].rtint)/* For a SUBREG rtx, SUBREG_REG extracts the value we want a subreg of.   SUBREG_WORD extracts the word-number.  */#define SUBREG_REG(RTX) ((RTX)->fld[0].rtx)#define SUBREG_WORD(RTX) ((RTX)->fld[1].rtint)/* Access various components of an ASM_OPERANDS rtx.  */#define ASM_OPERANDS_TEMPLATE(RTX) XSTR ((RTX), 0)#define ASM_OPERANDS_OUTPUT_CONSTRAINT(RTX) XSTR ((RTX), 1)#define ASM_OPERANDS_OUTPUT_IDX(RTX) XINT ((RTX), 2)#define ASM_OPERANDS_INPUT_VEC(RTX) XVEC ((RTX), 3)#define ASM_OPERANDS_INPUT_CONSTRAINT_VEC(RTX) XVEC ((RTX), 4)#define ASM_OPERANDS_INPUT(RTX, N) XVECEXP ((RTX), 3, (N))#define ASM_OPERANDS_INPUT_CONSTRAINT(RTX, N) XSTR (XVECEXP ((RTX), 4, (N)), 0)#define ASM_OPERANDS_INPUT_MODE(RTX, N) GET_MODE (XVECEXP ((RTX), 4, (N)))#define ASM_OPERANDS_SOURCE_FILE(RTX) XSTR ((RTX), 5)#define ASM_OPERANDS_SOURCE_LINE(RTX) XINT ((RTX), 6)/* For a MEM rtx, 1 if it's a volatile reference.   Also in an ASM_OPERANDS rtx.  */#define MEM_VOLATILE_P(RTX) ((RTX)->volatil)/* For a MEM rtx, 1 if it refers to a structure or union component.  */#define MEM_IN_STRUCT_P(RTX) ((RTX)->in_struct)/* For a SET rtx, SET_DEST is the place that is set   and SET_SRC is the value it is set to.  */#define SET_DEST(RTX) ((RTX)->fld[0].rtx)#define SET_SRC(RTX) ((RTX)->fld[1].rtx)/* 1 in a SYMBOL_REF if it addresses this function's constants pool.  */#define CONSTANT_POOL_ADDRESS_P(RTX) ((RTX)->unchanging)/* 1 in a SYMBOL_REF if it is the name of an external symbol.  */#define EXTERNAL_SYMBOL_P(RTX) ((RTX)->volatil)/* For an INLINE_HEADER rtx, FIRST_FUNCTION_INSN is the first insn   of the function that is not involved in copying parameters to   pseudo-registers.  FIRST_PARM_INSN is the very first insn of   the function, including the parameter copying.   We keep this around in case we must splice   this function into the assembly code at the end of the file.   FIRST_LABELNO is the first label number used by the function (inclusive).   LAST_LABELNO is the last label used by the function (exclusive).   MAX_REGNUM is the largest pseudo-register used by that function.   We want this to lay down like an INSN.  The PREV_INSN field   is always NULL.  The NEXT_INSN field always points to the   first function insn of the function being squirreled away.  */#define FIRST_FUNCTION_INSN(RTX) ((RTX)->fld[2].rtx)#define FIRST_PARM_INSN(RTX) ((RTX)->fld[3].rtx)#define FIRST_LABELNO(RTX) ((RTX)->fld[4].rtint)#define LAST_LABELNO(RTX) ((RTX)->fld[5].rtint)#define MAX_PARMREG(RTX) ((RTX)->fld[6].rtint)#define MAX_REGNUM(RTX) ((RTX)->fld[7].rtint)#define FUNCTION_ARGS_SIZE(RTX) ((RTX)->fld[8].rtint)/* Generally useful functions.  */extern rtx rtx_alloc ();extern rtvec rtvec_alloc ();extern rtx find_reg_note ();extern rtx gen_rtx ();extern rtx copy_rtx ();extern rtvec gen_rtvec ();extern rtvec gen_rtvec_v ();extern rtx gen_reg_rtx ();extern rtx gen_label_rtx ();extern rtx gen_inline_header_rtx ();extern rtx gen_lowpart ();extern rtx gen_highpart ();extern int subreg_lowpart_p ();extern rtx make_safe_from ();extern rtx memory_address ();extern rtx get_insns ();extern rtx get_last_insn ();extern rtx start_sequence ();extern rtx gen_sequence ();extern rtx expand_expr ();extern rtx output_constant_def ();extern rtx immed_real_const ();extern rtx immed_real_const_1 ();extern rtx immed_double_const ();extern rtx force_const_double_mem ();extern rtx force_const_mem ();extern rtx get_parm_real_loc ();extern rtx assign_stack_local ();extern rtx protect_from_queue ();extern void emit_queue ();extern rtx emit_move_insn ();extern rtx emit_insn ();extern rtx emit_jump_insn ();extern rtx emit_call_insn ();extern rtx emit_call_insn_before ();extern rtx emit_insn_before ();extern rtx emit_insn_after ();extern rtx emit_label ();extern rtx emit_barrier ();extern rtx emit_barrier_after ();extern rtx emit_note ();extern rtx emit_line_note ();extern rtx emit_line_note_force ();extern rtx prev_real_insn ();extern rtx next_real_insn ();extern rtx next_nondeleted_insn ();extern rtx plus_constant ();extern rtx find_equiv_reg ();extern rtx delete_insn ();extern rtx adj_offsettable_operand ();/* Maximum number of parallel sets and clobbers in any insn in this fn.   Always at least 3, since the combiner could put that many togetherm   and we want this to remain correct for all the remaining passes.  */extern int max_parallel;extern int asm_noperands ();extern char *decode_asm_operands ();#ifdef BITS_PER_WORD/* Conditional is to detect when config.h has been included.  */extern enum reg_class reg_preferred_class ();#endifextern rtx get_first_nonparm_insn ();/* Standard pieces of rtx, to be substituted directly into things.  */extern rtx pc_rtx;extern rtx cc0_rtx;extern rtx const0_rtx;extern rtx const1_rtx;extern rtx fconst0_rtx;extern rtx dconst0_rtx;/* Returns a constant 0 rtx in mode MODE.  */#define CONST0_RTX(MODE) \ ((MODE == SFmode) ? fconst0_rtx			\  : ((MODE == DFmode) ? dconst0_rtx			\     : ((GET_MODE_CLASS (MODE) == MODE_INT) ? const0_rtx	\        : (abort (), NULL_RTX))))/* All references to certain hard regs, except those created   by allocating pseudo regs into them (when that's possible),   go through these unique rtx objects.  */extern rtx stack_pointer_rtx;extern rtx frame_pointer_rtx;extern rtx arg_pointer_rtx;extern rtx struct_value_rtx;extern rtx struct_value_incoming_rtx;extern rtx static_chain_rtx;extern rtx static_chain_incoming_rtx;