Add --relax-float-ops and --convert-relaxed-to-half

The first pass applies the RelaxedPrecision decoration to all executable
instructions with float32 based type results. The second pass converts
all executable instructions with RelaxedPrecision result to the equivalent
float16 type, inserting converts where necessary.

Android.mk

@@ -88,6 +88,7 @@ SPVTOOLS_OPT_SRC_FILES := \
 		source/opt/composite.cpp \
 		source/opt/const_folding_rules.cpp \
 		source/opt/constants.cpp \
+		source/opt/convert_to_half_pass.cpp \
 		source/opt/copy_prop_arrays.cpp \
 		source/opt/dead_branch_elim_pass.cpp \
 		source/opt/dead_insert_elim_pass.cpp \
@@ -152,6 +153,7 @@ SPVTOOLS_OPT_SRC_FILES := \
 		source/opt/reduce_load_size.cpp \
 		source/opt/redundancy_elimination.cpp \
 		source/opt/register_pressure.cpp \
+		source/opt/relax_float_ops_pass.cpp \
 		source/opt/remove_duplicates_pass.cpp \
 		source/opt/replace_invalid_opc.cpp \
 		source/opt/scalar_analysis.cpp \

BUILD.gn

@@ -477,6 +477,8 @@ static_library("spvtools_opt") {
     "source/opt/const_folding_rules.h",
     "source/opt/constants.cpp",
     "source/opt/constants.h",
+    "source/opt/convert_to_half_pass.cpp",
+    "source/opt/convert_to_half_pass.h",
     "source/opt/copy_prop_arrays.cpp",
     "source/opt/copy_prop_arrays.h",
     "source/opt/dead_branch_elim_pass.cpp",
@@ -609,6 +611,8 @@ static_library("spvtools_opt") {
     "source/opt/reflect.h",
     "source/opt/register_pressure.cpp",
     "source/opt/register_pressure.h",
+    "source/opt/relax_float_ops_pass.cpp",
+    "source/opt/relax_float_ops_pass.h",
     "source/opt/remove_duplicates_pass.cpp",
     "source/opt/remove_duplicates_pass.h",
     "source/opt/replace_invalid_opc.cpp",

include/spirv-tools/optimizer.hpp

@@ -674,6 +674,22 @@ Optimizer::PassToken CreateLoopUnrollPass(bool fully_unroll, int factor = 0);
 // processed (see IsSSATargetVar for details).
 Optimizer::PassToken CreateSSARewritePass();
 
+// Create pass to convert relaxed precision instructions to half precision.
+// This pass converts as many relaxed float32 arithmetic operations to half as
+// possible. It converts any float32 operands to half if needed. It converts
+// any resulting half precision values back to float32 as needed. No variables
+// are changed. No image operations are changed.
+//
+// Best if run late since some optimizations may not handle half precision.
+// Best if followed by instruction simplification, redundancy elimination and
+// DCE.
+Optimizer::PassToken CreateConvertRelaxedToHalfPass();
+
+// Create relax float ops pass.
+// This pass decorates all float32 result instructions with RelaxedPrecision
+// if not already so decorated.
+Optimizer::PassToken CreateRelaxFloatOpsPass();
+
 // Create copy propagate arrays pass.
 // This pass looks to copy propagate memory references for arrays.  It looks
 // for specific code patterns to recognize array copies.

source/opt/CMakeLists.txt

@@ -26,6 +26,7 @@ set(SPIRV_TOOLS_OPT_SOURCES
   composite.h
   const_folding_rules.h
   constants.h
+  convert_to_half_pass.h
   copy_prop_arrays.h
   dead_branch_elim_pass.h
   dead_insert_elim_pass.h
@@ -92,6 +93,7 @@ set(SPIRV_TOOLS_OPT_SOURCES
   redundancy_elimination.h
   reflect.h
   register_pressure.h
+  relax_float_ops_pass.h
   remove_duplicates_pass.h
   replace_invalid_opc.h
   scalar_analysis.h
@@ -130,6 +132,7 @@ set(SPIRV_TOOLS_OPT_SOURCES
   composite.cpp
   const_folding_rules.cpp
   constants.cpp
+  convert_to_half_pass.cpp
   copy_prop_arrays.cpp
   dead_branch_elim_pass.cpp
   dead_insert_elim_pass.cpp
@@ -194,6 +197,7 @@ set(SPIRV_TOOLS_OPT_SOURCES
   reduce_load_size.cpp
   redundancy_elimination.cpp
   register_pressure.cpp
+  relax_float_ops_pass.cpp
   remove_duplicates_pass.cpp
   replace_invalid_opc.cpp
   scalar_analysis.cpp