intel/compiler: Relax some conditions in try_copy_propagate

Previously can_do_source_mods was used to determine whether a value with
a source modifier or a value from a scalar source (e.g., a uniform)
could be copy propagated.  The former is a superset of the latter, so
this always produces correct results, but it is overly restrictive.  For
example, a BFI instruction can't have source modifiers, but it can have
scalar sources.

This was originally authored to prevent a small number of shader-db
regressions in a commit that marked SHR has not being able to have
source modifiers.  That commit has since been dropped in favor of a
different method.

v2: Refactor register region restriction detection to a helper function.
Suggested by Jason.

No fossil-db changes on any Intel platform.

All Gen7+ platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 20039111 -> 20038943 (<.01%)
instructions in affected programs: 31736 -> 31568 (-0.53%)
helped: 104
HURT: 0
helped stats (abs) min: 1 max: 9 x̄: 1.62 x̃: 1
helped stats (rel) min: 0.30% max: 0.88% x̄: 0.45% x̃: 0.42%
95% mean confidence interval for instructions value: -2.03 -1.20
95% mean confidence interval for instructions %-change: -0.47% -0.42%
Instructions are helped.

total cycles in shared programs: 980309750 -> 980308897 (<.01%)
cycles in affected programs: 591078 -> 590225 (-0.14%)
helped: 70
HURT: 26
helped stats (abs) min: 2 max: 622 x̄: 23.94 x̃: 4
helped stats (rel) min: <.01% max: 2.85% x̄: 0.33% x̃: 0.12%
HURT stats (abs)   min: 2 max: 520 x̄: 31.65 x̃: 6
HURT stats (rel)   min: 0.02% max: 2.45% x̄: 0.34% x̃: 0.15%
95% mean confidence interval for cycles value: -26.41 8.64
95% mean confidence interval for cycles %-change: -0.27% -0.03%
Inconclusive result (value mean confidence interval includes 0).

No shader-db changes on earlier Intel platforms.

Reviewed-by: Anuj Phogat anuj.phogat@gmail.com [v1]
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9237>

src/intel/compiler/brw_ir.h

@@ -101,6 +101,12 @@ struct backend_instruction : public exec_node {
    bool reads_accumulator_implicitly() const;
    bool writes_accumulator_implicitly(const struct gen_device_info *devinfo) const;
 
+   /**
+    * Instructions that use indirect addressing have additional register
+    * regioning restrictions.
+    */
+   bool uses_indirect_addressing() const;
+
    void remove(bblock_t *block);
    void insert_after(bblock_t *block, backend_instruction *inst);
    void insert_before(bblock_t *block, backend_instruction *inst);