[PATCH] D117238: [C2x] Add BITINT_MAXWIDTH support

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman created this revision.
aaron.ballman added reviewers: erichkeane, jyknight, rsmith.
Herald added a subscriber: dschuff.
aaron.ballman requested review of this revision.
Herald added a subscriber: aheejin.
Herald added a project: clang.

Part of the `_BitInt` feature in C2x (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2763.pdf) is a new macro in limits.h named `BITINT_MAXWIDTH` that can be used to determine the maximum width of a bit-precise integer type. This macro must expand to a value that is at least as large as `ULLONG_WIDTH`.

This adds an implementation-defined macro named `__BITINT_MAXWIDTH__` to specify that value, which is used by limits.h for the standard macro. This gives us a migration path in the future should a target ever need to support something different than `llvm::IntegerType::MAX_INT_BITS`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117238

Files:
  clang/lib/Frontend/InitPreprocessor.cpp
  clang/lib/Headers/limits.h
  clang/lib/Sema/SemaType.cpp
  clang/test/Headers/limits.cpp
  clang/test/Preprocessor/init-aarch64.c
  clang/test/Preprocessor/init.c


Index: clang/test/Preprocessor/init.c
===================================================================
--- clang/test/Preprocessor/init.c
+++ clang/test/Preprocessor/init.c
@@ -1520,6 +1520,7 @@
 // WEBASSEMBLY-NEXT:#define __ATOMIC_RELEASE 3
 // WEBASSEMBLY-NEXT:#define __ATOMIC_SEQ_CST 5
 // WEBASSEMBLY-NEXT:#define __BIGGEST_ALIGNMENT__ 16
+// WEBASSEMBLY-NEXT:#define __BITINT_MAXWIDTH__ 8388608
 // WEBASSEMBLY-NEXT:#define __BOOL_WIDTH__ 8
 // WEBASSEMBLY-NEXT:#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 // WEBASSEMBLY-NEXT:#define __CHAR16_TYPE__ unsigned short
Index: clang/test/Preprocessor/init-aarch64.c
===================================================================
--- clang/test/Preprocessor/init-aarch64.c
+++ clang/test/Preprocessor/init-aarch64.c
@@ -40,6 +40,7 @@
 // AARCH64-NEXT: #define __ATOMIC_SEQ_CST 5
 // AARCH64:      #define __BIGGEST_ALIGNMENT__ 16
 // AARCH64_BE-NEXT: #define __BIG_ENDIAN__ 1
+// AARCH64-NEXT: #define __BITINT_MAXWIDTH__ 8388608
 // AARCH64-NEXT: #define __BOOL_WIDTH__ 8
 // AARCH64_BE-NEXT: #define __BYTE_ORDER__ __ORDER_BIG_ENDIAN__
 // AARCH64_LE-NEXT: #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
Index: clang/test/Headers/limits.cpp
===================================================================
--- clang/test/Headers/limits.cpp
+++ clang/test/Headers/limits.cpp
@@ -74,8 +74,11 @@
 _Static_assert(ULLONG_WIDTH / CHAR_BIT == sizeof(unsigned long long));
 _Static_assert(LLONG_WIDTH == ULLONG_WIDTH);
 _Static_assert(LLONG_WIDTH / CHAR_BIT == sizeof(signed long long));
+
+_Static_assert(BITINT_MAXWIDTH >= ULLONG_WIDTH);
 #else
 /* None of these are defined. */
 int BOOL_WIDTH, CHAR_WIDTH, SCHAR_WIDTH, UCHAR_WIDTH, USHRT_WIDTH, SHRT_WIDTH,
-    UINT_WIDTH, INT_WIDTH, ULONG_WIDTH, LONG_WIDTH, ULLONG_WIDTH, LLONG_WIDTH;
+    UINT_WIDTH, INT_WIDTH, ULONG_WIDTH, LONG_WIDTH, ULLONG_WIDTH, LLONG_WIDTH,
+    BITINT_MAXWIDTH;
 #endif
Index: clang/lib/Sema/SemaType.cpp
===================================================================
--- clang/lib/Sema/SemaType.cpp
+++ clang/lib/Sema/SemaType.cpp
@@ -2267,6 +2267,10 @@
     return QualType();
   }
 
+  // The max size of a _BitInt is exposed to the user via the
+  // __BITINT_MAXWIDTH__ macro from InitPreprocessor.cpp. If someday a target
+  // needs to pick a different max value, be sure to update
+  // InitializePredefinedMacros() as well.
   if (NumBits > llvm::IntegerType::MAX_INT_BITS) {
     Diag(Loc, diag::err_bit_int_max_size)
         << IsUnsigned << llvm::IntegerType::MAX_INT_BITS;
Index: clang/lib/Headers/limits.h
===================================================================
--- clang/lib/Headers/limits.h
+++ clang/lib/Headers/limits.h
@@ -78,6 +78,8 @@
 #define LONG_WIDTH   __LONG_WIDTH__
 #define ULLONG_WIDTH __LLONG_WIDTH__
 #define LLONG_WIDTH  __LLONG_WIDTH__
+
+#define BITINT_MAXWIDTH __BITINT_MAXWIDTH__
 #endif
 
 #ifdef __CHAR_UNSIGNED__  /* -funsigned-char */
Index: clang/lib/Frontend/InitPreprocessor.cpp
===================================================================
--- clang/lib/Frontend/InitPreprocessor.cpp
+++ clang/lib/Frontend/InitPreprocessor.cpp
@@ -25,6 +25,7 @@
 #include "clang/Serialization/ASTReader.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
 using namespace clang;
 
 static bool MacroBodyEndsInBackslash(StringRef MacroBody) {
@@ -914,6 +915,12 @@
   Builder.defineMacro("__LONG_WIDTH__", Twine(TI.getLongWidth()));
   Builder.defineMacro("__LLONG_WIDTH__", Twine(TI.getLongLongWidth()));
 
+  // The max size of a _BitInt is limited in SemaType.cpp to this value. If
+  // someday a target needs to pick a different value for this macro, be sure
+  // to update Sema::BuildBitIntType() as well.
+  Builder.defineMacro("__BITINT_MAXWIDTH__",
+                      Twine(llvm::IntegerType::MAX_INT_BITS));
+
   DefineTypeSize("__SCHAR_MAX__", TargetInfo::SignedChar, TI, Builder);
   DefineTypeSize("__SHRT_MAX__", TargetInfo::SignedShort, TI, Builder);
   DefineTypeSize("__INT_MAX__", TargetInfo::SignedInt, TI, Builder);


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