[PATCH] D86339: Enable constexpr on BITREVERSE builtin intrinsics (PR47249)

[Simon Pilgrim via Phabricator via cfe-commits]

RKSimon created this revision.
RKSimon added reviewers: rsmith, craig.topper, spatel.
Herald added a project: clang.
RKSimon requested review of this revision.

This enables us to use the __builtin_bitreverse 8/16/32/64 intrinsics inside constexpr code.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86339

Files:
  clang/docs/ReleaseNotes.rst
  clang/lib/AST/ExprConstant.cpp
  clang/test/Sema/constant-builtins-2.c


Index: clang/test/Sema/constant-builtins-2.c
===================================================================
--- clang/test/Sema/constant-builtins-2.c
+++ clang/test/Sema/constant-builtins-2.c
@@ -169,6 +169,11 @@
 char parity9[__builtin_parityl(1L << (BITSIZE(long) - 1)) == 1 ? 1 : -1];
 char parity10[__builtin_parityll(1LL << (BITSIZE(long long) - 1)) == 1 ? 1 : -1];
 
+char bitreverse1[__builtin_bitreverse8(0x01) == 0x80 ? 1 : -1];
+char bitreverse2[__builtin_bitreverse16(0x3C48) == 0x123C ? 1 : -1];
+char bitreverse3[__builtin_bitreverse32(0x12345678) == 0x1E6A2C48 ? 1 : -1];
+char bitreverse4[__builtin_bitreverse64(0x0123456789ABCDEFULL) == 0xF7B3D591E6A2C480 ? 1 : -1];
+
 char ffs1[__builtin_ffs(0) == 0 ? 1 : -1];
 char ffs2[__builtin_ffs(1) == 1 ? 1 : -1];
 char ffs3[__builtin_ffs(0xfbe71) == 1 ? 1 : -1];
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -11180,6 +11180,17 @@
     return Success(AlignedVal, E);
   }
 
+  case Builtin::BI__builtin_bitreverse8:
+  case Builtin::BI__builtin_bitreverse16:
+  case Builtin::BI__builtin_bitreverse32:
+  case Builtin::BI__builtin_bitreverse64: {
+    APSInt Val;
+    if (!EvaluateInteger(E->getArg(0), Val, Info))
+      return false;
+
+    return Success(Val.reverseBits(), E);
+  }
+
   case Builtin::BI__builtin_bswap16:
   case Builtin::BI__builtin_bswap32:
   case Builtin::BI__builtin_bswap64: {
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -56,7 +56,9 @@
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 
-- ...
+- The builtin intrinsics ``__builtin_bitreverse8``, ``__builtin_bitreverse``,
+  ``__builtin_bitreverse32`` and ``__builtin_bitreverse64`` may now be used
+  within constexpr expressions.
 
 New Compiler Flags
 ------------------


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