We already compute the "first" and "last" basic block that
uses a value, so we could know when to hoist a value into
a var declaration. You have to do this sometimes to make
sure all uses are in scope of the declaration.
Until now we tracked Phis with an entirely different mechanism.
But there are cases which broke down. That's what happens
in crbug.com/tint/1649.
Additionally, GraphicsFuzz cases generarte similar weirdness.
Also, be more careful about ensuring that the assignments
generated to feed phis behave as if they occur in parallel.
Within a single batch of such assignments, generate and
use intermediate let-declarations for phis that that batch
will overwrite.
Also, unwrap-references when rectifying the signedness of
binary operators.
Skip tests that fail due to crbug.comt/tint/98:
test/tint/bug/tint/749.spvasm.*
Fixed: tint:1649
Change-Id: I7314c351b74a10bfa9a18011f3d80a520568011c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/101220
Auto-Submit: David Neto <dneto@google.com>
Commit-Queue: David Neto <dneto@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
a3f2bf6c60