[Sema] Mark implicitly-inserted ICE's as being part of explicit cast (PR38166)

Summary:
As discussed in [[ https://bugs.llvm.org/show_bug.cgi?id=38166 | PR38166 ]], we need to be able to distinqush whether the cast
we are visiting is actually a cast, or part of an `ExplicitCast`.
There are at least four ways to get there:
1. Introduce a new `CastKind`, and use it instead of `IntegralCast` if we are in `ExplicitCast`.

   Would work, but does not scale - what if we will need more of these cast kinds?
2. Introduce a flag in `CastExprBits`, whether this cast is part of `ExplicitCast` or not.

   Would work, but it isn't immediately clear where it needs to be set.
2. Fix `ScalarExprEmitter::VisitCastExpr()` to visit these `NoOp` casts.

   As pointed out by @rsmith, CodeGenFunction::EmitMaterializeTemporaryExpr calls

   skipRValueSubobjectAdjustments, which steps over the CK_NoOp cast`,

   which explains why we currently don't visit those.

   This is probably impossible, as @efriedma points out, that is intentional as per `[class.temporary]` in the standard
3. And the simplest one, just record which NoOp casts we skip.

   It just kinda works as-is afterwards.

But, the approach with a flag is the least intrusive one, and is probably the best one overall.

Reviewers: rsmith, rjmccall, majnemer, efriedma

Reviewed By: rsmith

Subscribers: cfe-commits, aaron.ballman, vsk, llvm-commits, rsmith

Differential Revision: https://reviews.llvm.org/D49508

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/test/SemaOpenCL/multistep-explicit-cast.cl b/clang/test/SemaOpenCL/multistep-explicit-cast.cl
new file mode 100644
index 00000000000..5e3d12a0e44
--- /dev/null
+++ b/clang/test/SemaOpenCL/multistep-explicit-cast.cl
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -fsyntax-only -ast-dump %s | FileCheck %s
+// expected-no-diagnostics
+
+typedef __attribute__((ext_vector_type(2)))  char char2;
+
+void vectorIncrementDecrementOps() {
+  // CHECK: FunctionDecl {{.*}} <{{.*}}, line:{{.*}}> line:{{.*}} vectorIncrementDecrementOps 'void (void)'{{$}}
+  // CHECK: CStyleCastExpr {{.*}} <col:{{.*}}> 'char2':'char __attribute__((ext_vector_type(2)))' <VectorSplat>{{$}}
+  // CHECK-NEXT: ImplicitCastExpr {{.*}} <col:{{.*}}> 'char' <IntegralCast> part_of_explicit_cast{{$}}
+  // CHECK-NEXT: IntegerLiteral {{.*}} <col:{{.*}}> 'int' 1{{$}}
+  char2 A = (char2)(1);
+  A++;
+}