poly_int: DWARF locations

This patch adds support for DWARF location expressions
that involve polynomial offsets.  It adds a target hook that
says how the runtime invariants used in the offsets should be
represented in DWARF.  SVE vectors have to be a multiple of
128 bits in size, so the GCC port uses the number of 128-bit
blocks minus one as the runtime invariant.  However, in DWARF,
the vector length is exposed via a pseudo "VG" register that
holds the number of 64-bit elements in a vector.  Thus:

  indeterminate 1 == (VG / 2) - 1

The hook needs to be general enough to express this.
Note that in most cases the division and subtraction fold
away into surrounding expressions.

2017-12-20  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* target.def (dwarf_poly_indeterminate_value): New hook.
	* targhooks.h (default_dwarf_poly_indeterminate_value): Declare.
	* targhooks.c (default_dwarf_poly_indeterminate_value): New function.
	* doc/tm.texi.in (TARGET_DWARF_POLY_INDETERMINATE_VALUE): Document.
	* doc/tm.texi: Regenerate.
	* dwarf2out.h (build_cfa_loc, build_cfa_aligned_loc): Take the
	offset as a poly_int64.
	* dwarf2out.c (new_reg_loc_descr): Move later in file.  Take the
	offset as a poly_int64.
	(loc_descr_plus_const, loc_list_plus_const, build_cfa_aligned_loc):
	Take the offset as a poly_int64.
	(build_cfa_loc): Likewise.  Use loc_descr_plus_const.
	(frame_pointer_fb_offset): Change to a poly_int64.
	(int_loc_descriptor): Take the offset as a poly_int64.  Use
	targetm.dwarf_poly_indeterminate_value for polynomial offsets.
	(based_loc_descr): Take the offset as a poly_int64.
	Use strip_offset_and_add to handle (plus X (const)).
	Use new_reg_loc_descr instead of an open-coded version of the
	previous implementation.
	(mem_loc_descriptor): Handle CONST_POLY_INT.
	(compute_frame_pointer_to_fb_displacement): Take the offset as a
	poly_int64.  Use strip_offset_and_add to handle (plus X (const)).

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r255868

2 files changed, 15 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index fc73bb2..434c42a 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -3130,6 +3130,19 @@ the CFI label attached to the insn, @var{pattern} is the pattern of
 the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
 @end deftypefn
 
+@deftypefn {Target Hook} {unsigned int} TARGET_DWARF_POLY_INDETERMINATE_VALUE (unsigned int @var{i}, unsigned int *@var{factor}, int *@var{offset})
+Express the value of @code{poly_int} indeterminate @var{i} as a DWARF
+expression, with @var{i} counting from 1.  Return the number of a DWARF
+register @var{R} and set @samp{*@var{factor}} and @samp{*@var{offset}} such
+that the value of the indeterminate is:
+@smallexample
+value_of(@var{R}) / @var{factor} - @var{offset}
+@end smallexample
+
+A target only needs to define this hook if it sets
+@samp{NUM_POLY_INT_COEFFS} to a value greater than 1.
+@end deftypefn
+
 @defmac INCOMING_FRAME_SP_OFFSET
 A C expression whose value is an integer giving the offset, in bytes,
 from the value of the stack pointer register to the top of the stack
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index ff00673..c1d2a8c 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -2544,6 +2544,8 @@ terminate the stack backtrace.  New ports should avoid this.
 
 @hook TARGET_DWARF_HANDLE_FRAME_UNSPEC
 
+@hook TARGET_DWARF_POLY_INDETERMINATE_VALUE
+
 @defmac INCOMING_FRAME_SP_OFFSET
 A C expression whose value is an integer giving the offset, in bytes,
 from the value of the stack pointer register to the top of the stack