SSA rewrite pass.

This pass replaces the load/store elimination passes.  It implements the
SSA re-writing algorithm proposed in

     Simple and Efficient Construction of Static Single Assignment Form.
     Braun M., Buchwald S., Hack S., Leißa R., Mallon C., Zwinkau A. (2013)
     In: Jhala R., De Bosschere K. (eds)
     Compiler Construction. CC 2013.
     Lecture Notes in Computer Science, vol 7791.
     Springer, Berlin, Heidelberg

     https://link.springer.com/chapter/10.1007/978-3-642-37051-9_6

In contrast to common eager algorithms based on dominance and dominance
frontier information, this algorithm works backwards from load operations.

When a target variable is loaded, it queries the variable's reaching
definition.  If the reaching definition is unknown at the current location,
it searches backwards in the CFG, inserting Phi instructions at join points
in the CFG along the way until it finds the desired store instruction.

The algorithm avoids repeated lookups using memoization.

For reducible CFGs, which are a superset of the structured CFGs in SPIRV,
this algorithm is proven to produce minimal SSA.  That is, it inserts the
minimal number of Phi instructions required to ensure the SSA property, but
some Phi instructions may be dead
(https://en.wikipedia.org/wiki/Static_single_assignment_form).

1 files changed, 1 insertions, 0 deletions

diff --git a/Android.mk b/Android.mk
index 04a84a17..ec2a0f07 100644
--- a/Android.mk
+++ b/Android.mk
@@ -118,6 +118,7 @@ SPVTOOLS_OPT_SRC_FILES := \
 		source/opt/scalar_replacement_pass.cpp \
 		source/opt/set_spec_constant_default_value_pass.cpp \
 		source/opt/simplification_pass.cpp \
+		source/opt/ssa_rewrite_pass.cpp \
 		source/opt/strength_reduction_pass.cpp \
 		source/opt/strip_debug_info_pass.cpp \
 		source/opt/strip_reflect_info_pass.cpp \