[clang] [Clang] Add predefined macros for integer constants to implement section 7.18.4 of ISO/IEC 9899:1999 in `<stdint.h>` in a safe way (PR #123514)

[Manuel Sainz de Baranda y Goñi via cfe-commits]

https://github.com/redcode updated https://github.com/llvm/llvm-project/pull/123514

>From 507b9804cc748a2441db8d1eb36a01be34bc21ce Mon Sep 17 00:00:00 2001
From: redcode <manuel at zxe.io>
Date: Sun, 19 Jan 2025 15:29:01 +0100
Subject: [PATCH] [Clang] Add predefined macros `__INT<N>_C`, `__UINT<N>_C`,
 `__INTMAX_C` and `__UINTMAX_C`

---
 clang/lib/Frontend/InitPreprocessor.cpp | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index 29723b573e771a..17f624e9645395 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -253,6 +253,8 @@ static void DefineExactWidthIntType(const LangOptions &LangOpts,
 
   StringRef ConstSuffix(TI.getTypeConstantSuffix(Ty));
   Builder.defineMacro(Prefix + Twine(TypeWidth) + "_C_SUFFIX__", ConstSuffix);
+  Builder.defineMacro(Prefix + Twine(TypeWidth) + "_C(c)",
+                      ConstSuffix.size() ? Twine("c##") + ConstSuffix : "c");
 }
 
 static void DefineExactWidthIntTypeSize(TargetInfo::IntType Ty,
@@ -1164,12 +1166,16 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
 
   DefineType("__INTMAX_TYPE__", TI.getIntMaxType(), Builder);
   DefineFmt(LangOpts, "__INTMAX", TI.getIntMaxType(), TI, Builder);
-  Builder.defineMacro("__INTMAX_C_SUFFIX__",
-                      TI.getTypeConstantSuffix(TI.getIntMaxType()));
+  StringRef ConstSuffix(TI.getTypeConstantSuffix(TI.getIntMaxType()));
+  Builder.defineMacro("__INTMAX_C_SUFFIX__", ConstSuffix);
+  Builder.defineMacro("__INTMAX_C(c)",
+                      ConstSuffix.size() ? Twine("c##") + ConstSuffix : "c");
   DefineType("__UINTMAX_TYPE__", TI.getUIntMaxType(), Builder);
   DefineFmt(LangOpts, "__UINTMAX", TI.getUIntMaxType(), TI, Builder);
-  Builder.defineMacro("__UINTMAX_C_SUFFIX__",
-                      TI.getTypeConstantSuffix(TI.getUIntMaxType()));
+  ConstSuffix = TI.getTypeConstantSuffix(TI.getUIntMaxType());
+  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);