Add in individual flags for Vulkan <-> WebGPU passes (#2615)

Adds flags and/or documentation for individual transformation passes
that had been missed in previous patches.

Fixes #2574

source/opt/optimizer.cpp

@@ -472,6 +472,10 @@ bool Optimizer::RegisterPassFromFlag(const std::string& flag) {
     RegisterPass(CreateGenerateWebGPUInitializersPass());
   } else if (pass_name == "legalize-vector-shuffle") {
     RegisterPass(CreateLegalizeVectorShufflePass());
+  } else if (pass_name == "split-invalid-unreachable") {
+    RegisterPass(CreateLegalizeVectorShufflePass());
+  } else if (pass_name == "decompose-initialized-variables") {
+    RegisterPass(CreateDecomposeInitializedVariablesPass());
   } else {
     Errorf(consumer(), nullptr, {},
            "Unknown flag '--%s'. Use --help for a list of valid flags",

tools/opt/opt.cpp

@@ -140,6 +140,12 @@ Options (in lexicographical order):)",
                another.  It will only propagate an array if the source is never
                written to, and the only store to the target is the copy.)");
   printf(R"(
+  --decompose-initialized-variables
+               Decomposes initialized variable declarations into a declaration
+               followed by a store of the initial value. This is done to work
+               around known issues with some Vulkan drivers for initialize
+               variables.)");
+  printf(R"(
   --eliminate-common-uniform
                Perform load/load elimination for duplicate uniform values.
                Converts any constant index access chain uniform loads into
@@ -228,6 +234,11 @@ Options (in lexicographical order):)",
                option --relax-logical-pointer to the validator.)",
          GetLegalizationPasses().c_str());
   printf(R"(
+  --legalize-vector-shuffle
+               Converts any usages of 0xFFFFFFFF for the literals in
+               OpVectorShuffle to a literal 0. This is done since 0xFFFFFFFF is
+               forbidden in WebGPU.)");
+  printf(R"(
   --local-redundancy-elimination
                Looks for instructions in the same basic block that compute the
                same value, and deletes the redundant ones.)");
@@ -398,6 +409,13 @@ Options (in lexicographical order):)",
                Will simplify all instructions in the function as much as
                possible.)");
   printf(R"(
+  --split-invalid-unreachable
+               Attempts to legalize for WebGPU cases where an unreachable
+               merge-block is also a continue-target by splitting it into two
+               seperate blocks. There exist legal, for Vulkan, instances of this
+               pattern that cannot be converted into legal WebGPU, so this
+               conversion may not succeed.)");
+  printf(R"(
   --skip-validation
                Will not validate the SPIR-V before optimizing.  If the SPIR-V
                is invalid, the optimizer may fail or generate incorrect code.