[PATCH] D68824: Fix __builtin_assume_aligned with too large values.

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added a comment.

This seems to be missing a CodeGen test for what IR we generate on an overly-large alignment. (The warning says the alignment is ignored, but I don't see where you're actually doing anything different in that case when generating IR.)



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Comment at: clang/include/clang/Basic/DiagnosticSemaKinds.td:2857-2859
+    : Warning<"requested alignment must be %0 bytes or smaller; assumption "
+              "ignored">,
+      InGroup<DiagGroup<"builtin-assume-aligned-alignment">>;
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Ignoring the assumption in this case seems unnecessarily user-hostile (and would require hard-coding an arbitrary LLVM limit in the source code to work around). Couldn't we just assume the highest alignment that we do support instead?


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Comment at: clang/lib/CodeGen/CGStmtOpenMP.cpp:1522
   for (const auto *Clause : D.getClausesOfKind<OMPAlignedClause>()) {
-    unsigned ClauseAlignment = 0;
+    size_t ClauseAlignment = 0;
     if (const Expr *AlignmentExpr = Clause->getAlignment()) {
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It's not appropriate to assume that `size_t` is any bigger than `unsigned` or generally that it's meaningful on the target. If you want 64 bits here, use `uint64_t`, but the right choice is probably `llvm::APInt`.


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Comment at: clang/lib/Sema/SemaChecking.cpp:6067-6070
+    // Alignment calculations can wrap around if it's greater than 2**28.
+    unsigned MaximumAlignment =
+        Context.getTargetInfo().getTriple().isOSBinFormatCOFF() ? 8192
+                                                                : 268435456;
----------------
Why is there a different limit depending on bin format? We can support this at the IR level regardless, can't we? (I don't see how the binary format is relevant.)


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  https://reviews.llvm.org/D68824/new/

https://reviews.llvm.org/D68824