Generalize dead stores.
Generalize dead stores.

Stores are dead if the address is from an alloca and all uses of the
address are stores, not just when it's a single store.

Change-Id: I5b65a64e21b9e398922e5440c35f0d318c03e911
Reviewed-on: https://swiftshader-review.googlesource.com/8574
Tested-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>

bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader