[PATCH] D120770: [C2x] Implement literal suffixes for _BitInt

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: clang/include/clang/Lex/LiteralSupport.h:65
   bool isLong : 1;          // This is *not* set for long long.
   bool isLongLong : 1;
   bool isSizeT : 1;         // 1z, 1uz (C++2b)
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erichkeane wrote:
> I can't help but wonder if there are some really good opportunities to merge a bunch of these mutually exclusive ones into an enum...
> ```
> enum class SizeType {
> Long,
> LongLong,
> SizeT,
> Float,
> Imaginary,
> Float16,
> Flaot128,
> Fract,
> Accum,
> BitInt
> ```
> 
> Or something?
That seems plausible, but perhaps as a follow-up. We're going from 12 bits to 13 with this patch (and correctly a layout issue as a drive-by), so we're not at or near an allocation unit boundary.


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Comment at: clang/lib/AST/StmtPrinter.cpp:1157
+  if (const auto *BT = Node->getType()->getAs<BitIntType>()) {
+    OS << (BT->isUnsigned() ? "uwb" : "wb");
+    return;
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erichkeane wrote:
> Nit: Instead of BT->isUnsigned(), we already have isSigned above.
Good call!


================
Comment at: clang/lib/Lex/LiteralSupport.cpp:903
+        break; // Invalid for floats.
+      if (HasSize)
+        break; // Invalid if we already have a size for the literal.
----------------
erichkeane wrote:
> Do we also have to reject isImaginary/isFract/etc separately?
I'm not super familiar with fixed-point literals, but at least with imaginary, you can make a _Complex from any integer type, including _BitInt, so I don't think there's a reason to reject that case.


================
Comment at: clang/lib/Sema/SemaExpr.cpp:3987
+              << Literal.isUnsigned;
+          Width = MaxBitIntWidth;
+        }
----------------
erichkeane wrote:
> Do you have some AST test here to see what happens to the value when the width is exceeded?
Not an AST test -- can't get one of those because this emits an error. But we do have a semantic test, see bitint-constants.c lines 135-136.


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Comment at: clang/lib/Sema/SemaExpr.cpp:3995
+        ResultVal = ResultVal.zextOrTrunc(Width);
+        Ty = Context.getBitIntType(Literal.isUnsigned, Width);
+      }
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erichkeane wrote:
> I think it is already covered, but do we make sure the literal itself and the suffix match?  That is: -111uwb is invalid?
We do not, but that's consistent with other suffix confusion: https://godbolt.org/z/rExPGdex3

(Remember, the `-` isn't part of the literal, that's a unary negation operator applied to the positive literal.)


================
Comment at: clang/test/AST/bitint-suffix.c:20
+  // CHECK: TypedefDecl 0x{{[^ ]*}} <col:3, col:28> col:28 zero_uwb 'typeof (0uwb)':'unsigned _BitInt(1)'
+  typedef __typeof__(0uwb) zero_uwb;
+  // CHECK: TypedefDecl 0x{{[^ ]*}} <col:3, col:29> col:29 neg_zero_uwb 'typeof (-0uwb)':'unsigned _BitInt(1)'
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erichkeane wrote:
> I think by my reading, wbu is valid as well, right?  Can we have 1 test for that?
We have one -- bitint-constant.c lines 89-92.


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Comment at: clang/test/Lexer/bitint-constants.c:133
+  // the width of BITINT_MAXWIDTH.
+  _Static_assert(__BITINT_MAXWIDTH__ <= 128,
+	             "Need to pick a bigger constant for the test case below.");
----------------
erichkeane wrote:
> <3
> 
> I'd also like a 'TODO' here when this happens that we have something to make sure that a 129bit/etc literal 'works' as expected. 
Added a comment.


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  https://reviews.llvm.org/D120770/new/

https://reviews.llvm.org/D120770