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Using type deduction to define __SIZE_TYPE__ and __PTRDIFF_TYPE__ #155979

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Using type deduction to define __SIZE_TYPE__ and __PTRDIFF_TYPE__ #155979

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da3d78a
Using type deduction to define __SIZE_TYPE__ and __PTRDIFF_TYPE__
YexuanXiao Aug 29, 2025
085cf65
Add tests
YexuanXiao Aug 31, 2025
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10 changes: 6 additions & 4 deletions clang/lib/Frontend/InitPreprocessor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1175,13 +1175,15 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
Builder.defineMacro("__UINTMAX_C_SUFFIX__", ConstSuffix);
Builder.defineMacro("__UINTMAX_C(c)",
ConstSuffix.size() ? Twine("c##") + ConstSuffix : "c");
DefineType("__PTRDIFF_TYPE__", TI.getPtrDiffType(LangAS::Default), Builder);
DefineFmt(LangOpts, "__PTRDIFF", TI.getPtrDiffType(LangAS::Default), TI,
Builder);
DefineType("__INTPTR_TYPE__", TI.getIntPtrType(), Builder);
DefineFmt(LangOpts, "__INTPTR", TI.getIntPtrType(), TI, Builder);
DefineType("__SIZE_TYPE__", TI.getSizeType(), Builder);
// Use deduction to obtain the built-in __size_t and __ptrdiff_t types instead
// of standard integer types
Builder.defineMacro("__SIZE_TYPE__", "__typeof(sizeof(0))");
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I don't have a good hold on whether this is a good idea or not. We should probably have an RFC for this.

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I enhanced the check for the %zu format specifier in #143653, but some people reported that it generated a lot of false positives. As a result, the check was eventually removed. The reason was that calculating skb->len - sizeof(_arph) loses all the sugar types. If the PR gets accepted, I can add a new option to enable this enhanced check (under the condition that the libc defines size_t in this way).

DefineFmt(LangOpts, "__SIZE", TI.getSizeType(), TI, Builder);
Builder.defineMacro("__PTRDIFF_TYPE__", "__typeof((int*)0-(int*)0)");
DefineFmt(LangOpts, "__PTRDIFF", TI.getPtrDiffType(LangAS::Default), TI,
Builder);
DefineType("__WCHAR_TYPE__", TI.getWCharType(), Builder);
DefineType("__WINT_TYPE__", TI.getWIntType(), Builder);
DefineTypeSizeAndWidth("__SIG_ATOMIC", TI.getSigAtomicType(), TI, Builder);
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