Fix FXC compile errors on divide by zero

FXC fails to compile when it determines that the rhs of an integral
division is zero with "error X4010: Unsigned integer divide by zero".

bclayton's fix (https://dawn-review.googlesource.com/c/tint/+/60500)
addressed cases for division by an integer constant 0. This CL adds the
missing support for division by integral vectors with 0 components.

FXC also fails on division by integral expressions that it can fold to
0. To handle these cases, we now emit a runtime check for 0 and replace
by 1. In the cases I've tested, FXC seems able to optimize these checks
away.

Bug: tint:1083
Change-Id: I02f08e9077882f03c1e42b62dacb742a48fa48ba
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/73580
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: David Neto <dneto@google.com>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>

src/sem/constant.cc

@@ -14,6 +14,7 @@
 
 #include "src/sem/constant.h"
 
+#include <functional>
 #include <utility>
 
 #include "src/debug.h"
@@ -61,5 +62,23 @@ Constant::~Constant() = default;
 
 Constant& Constant::operator=(const Constant& rhs) = default;
 
+bool Constant::AnyZero() const {
+  for (size_t i = 0; i < Elements().size(); ++i) {
+    if (WithScalarAt(i, [&](auto&& s) {
+          // Use std::equal_to to work around -Wfloat-equal warnings
+          auto equals_to =
+              std::equal_to<std::remove_reference_t<decltype(s)>>{};
+
+          if (equals_to(s, 0)) {
+            return true;
+          }
+          return false;
+        })) {
+      return true;
+    }
+  }
+  return false;
+}
+
 }  // namespace sem
 }  // namespace tint

src/sem/constant.h

@@ -97,6 +97,9 @@ class Constant {
   /// @returns the constant's scalar elements
   const Scalars& Elements() const { return elems_; }
 
+  /// @returns true if any scalar element is zero
+  bool AnyZero() const;
+
   /// Calls `func(s)` with s being the current scalar value at `index`.
   /// `func` is typically a lambda of the form '[](auto&& s)'.
   /// @param index the index of the scalar value