[CodeGen] Detect empty domain because of parameters context.

[CodeGen] Detect empty domain because of parameters context.

Isl does not allow generating isl_ast_expr from an isl_pw_aff that has an
empty domain (i.e. has no pieces). We already detected the case if the
isl_pw_aff comes with an empty domain.

isl_ast_build also considers the domain empty if it is disjoint with the
parameter context (e.g. parameters values that we exclude by runtime
versioning).

Intersect the access relation domain with the parameter context to
also detect such practically empty access domains. The effective
pointer used in the generated code is unimportand because it will never
be executed.

This fixes llvm.org/PR35362

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@318806 91177308-0d34-0410-b5e6-96231b3b80d8