[all-commits] [llvm/llvm-project] 349636: Implement VectorType conditional operator GNU exte...

[Erich Keane via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 349636d2bfc39a5c81a835a95d203a42d9f9301a
      https://github.com/llvm/llvm-project/commit/349636d2bfc39a5c81a835a95d203a42d9f9301a
  Author: Erich Keane <erich.keane at intel.com>
  Date:   2020-01-13 (Mon, 13 Jan 2020)

  Changed paths:
    M clang/docs/LanguageExtensions.rst
    M clang/include/clang/AST/Expr.h
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/include/clang/Sema/Sema.h
    M clang/lib/AST/ExprConstant.cpp
    M clang/lib/CodeGen/CGExprScalar.cpp
    M clang/lib/Sema/SemaExprCXX.cpp
    A clang/test/CodeGenCXX/vector-conditional.cpp
    M clang/test/Sema/vector-gcc-compat.cpp
    A clang/test/SemaCXX/vector-conditional.cpp

  Log Message:
  -----------
  Implement VectorType conditional operator GNU extension.

GCC supports the conditional operator on VectorTypes that acts as a
'select' in C++ mode. This patch implements the support. Types are
converted as closely to GCC's behavior as possible, though in a few
places consistency with our existing vector type support was preferred.

Note that this implementation is different from the OpenCL version in a
number of ways, so it unfortunately required a different implementation.

First, the SEMA rules and promotion rules are significantly different.

Secondly, GCC implements COND[i] != 0 ? LHS[i] : RHS[i] (where i is in
the range 0- VectorSize, for each element).  In OpenCL, the condition is
COND[i] < 0 ? LHS[i]: RHS[i].

In the process of implementing this, it was also required to make the
expression COND ? LHS : RHS type dependent if COND is type dependent,
since the type is now dependent on the condition.  For example:

    T ? 1 : 2;

Is not typically type dependent, since the result can be deduced from
the operands.  HOWEVER, if T is a VectorType now, it could change this
to a 'select' (basically a swizzle with a non-constant mask) with the 1
and 2 being promoted to vectors themselves.

While this is a change, it is NOT a standards incompatible change. Based
on my (and D. Gregor's, at the time of writing the code) reading of the
standard, the expression is supposed to be type dependent if ANY
sub-expression is type dependent.

Differential Revision: https://reviews.llvm.org/D71463