[compiler-rt] [llvm] [flang] [clang] [clang-tools-extra] [clang] Add support for new loop attribute [[clang::code_align()]] (PR #70762)

[Erich Keane via cfe-commits]

================
@@ -322,6 +322,71 @@ static Attr *handleUnlikely(Sema &S, Stmt *St, const ParsedAttr &A,
   return ::new (S.Context) UnlikelyAttr(S.Context, A);
 }
 
+CodeAlignAttr *Sema::BuildCodeAlignAttr(const AttributeCommonInfo &CI,
+                                        Expr *E) {
+  if (!E->isValueDependent()) {
+    llvm::APSInt ArgVal;
+    ExprResult Res = VerifyIntegerConstantExpression(E, &ArgVal);
+    if (Res.isInvalid())
+      return nullptr;
+    E = Res.get();
+
+    // This attribute requires an integer argument which is a constant power of
+    // two between 1 and 4096 inclusive.
+    if (ArgVal < CodeAlignAttr::MinimumAlignment ||
+	ArgVal > CodeAlignAttr::MaximumAlignment ||
+        (ArgVal < CodeAlignAttr::MaximumAlignment && !ArgVal.isPowerOf2())) {
+      if (std::optional<int64_t> Value = ArgVal.trySExtValue())
+        Diag(CI.getLoc(), diag::err_attribute_power_of_two_in_range)
+            << CI << CodeAlignAttr::MinimumAlignment
+            << CodeAlignAttr::MaximumAlignment << Value.value();
+      else
+        Diag(CI.getLoc(), diag::err_attribute_power_of_two_in_range)
+            << CI << CodeAlignAttr::MinimumAlignment
+            << CodeAlignAttr::MaximumAlignment << E;
+      return nullptr;
+    }
+  }
+  return new (Context) CodeAlignAttr(Context, CI, E);
+}
+
+static Attr *handleCodeAlignAttr(Sema &S, Stmt *St, const ParsedAttr &A) {
+
+  Expr *E = A.getArgAsExpr(0);
+  return S.BuildCodeAlignAttr(A, E);
+}
+
+// Emit duplicate error for [[clang::code_align()]] attribute.
+static void CheckForDuplicateCodeAlignAttrs(Sema &S,
+                                            ArrayRef<const Attr *> Attrs) {
+  // Create a list of CodeAlign attributes only.
+  SmallVector<const CodeAlignAttr *, 8> OnlyCodeAlignAttrs;
----------------
erichkeane wrote:

Sorry, just looked at this again.  What is the point of going through all of this?  I would expect a simpler algorithm to be (obviously pseudo code):


```
auto *FirstItr = std::find_if(Attrs.begin(), Attrs.end(), [](const Attr *A) { return isa<const CodeAlignAttr>(A); });
if (FirstItr == Attrs.end()) // no attributes found
  return;
auto *SecondItr = std::find_if(FirstItr + 1, Attrs.end(), [](const Attr *A) { return isa<const CodeAlignAttr>(A); });
if (SecondItr == Attrs.end()) // only 1 attribute found)
  return;

// diagnose here.

```

If you still want to diagnose EVERY duplicate, you can put the 2nd find_if in a loop there instead of as an if.

https://github.com/llvm/llvm-project/pull/70762