More aggressively prune unreachable code as follows.
When no control flow edges reach a merge block or continue target:
- delete their contents so that:
- a merge block becomes OpLabel, then OpUnreachable
- a continue target becomes OpLabel, then an OpBranch back to the
loop header
- any basic block which is dominated by such a merge block or continue
target is removed as well.
- decorations targeting the removed instructions are removed.
Enables the SPIR-V builder post-processing step the GLSLANG_WEB case.
A removed block releases its instructions, so Module::idToInstruction
suddenly contains dangling references. The original motivation for
block removal was to skip some unreachable blocks, but that's already
achieved by InReadableOrder.cpp.
Also updated stale comments.
To ensure back branches always go to a header block, create a header
block even for !testFirst loops. Then unify common code between the
testFirst/!testFirst cases.
Generate the header-block code first, so update golden files.
Realize that certain infinite loops generate invalid SPIR-V, so put a
TODO to instead abort code generation in such cases.
Change-Id: I1e173c8f73daad186cfc666b7d72bd563ed7665d
