[clang] [CIR] Add support for __builtin_assume_aligned (PR #152152)

[Bruno Cardoso Lopes via cfe-commits]

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@@ -3143,6 +3143,45 @@ def CIR_AssumeOp : CIR_Op<"assume"> {
   }];
 }
 
+def CIR_AssumeAlignedOp : CIR_Op<"assume_aligned", [
+  Pure, AllTypesMatch<["pointer", "result"]>
+]> {
+  let summary = "Tell the optimizer that a pointer is aligned";
+  let description = [{
+    The `cir.assume_aligned` operation takes two or three arguments. The first
+    argument `pointer` gives the pointer value whose alignment is to be assumed,
+    and the second argument `align` is an integer attribute that gives the
+    assumed alignment.
+
+    The `offset` argument is optional. If given, it represents misalignment
+    offset. When it's present, this operation tells the optimizer that the
+    pointer is always misaligned to the alignment by `offset` bytes, a.k.a. the
+    pointer yielded by `(char *)pointer - offset` is aligned to the specified
+    alignment. Note that the `offset` argument is an SSA value rather than an
+    attribute, which means that you could pass a dynamically determined value
+    as the mialignment offset.
+
+    The result of this operation has the same value as the `pointer` argument,
+    but it additionally carries any alignment information indicated by this
+    operation.
+
+    This operation corresponds to the `__builtin_assume_aligned` builtin
+    function.
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bcardosolopes wrote:

Can you please add a small example?

https://github.com/llvm/llvm-project/pull/152152