[clang] [compiler-rt] [ubsan] Display correct runtime messages for negative _BitInt (PR #96240)

[Jakub Jelínek via llvm-commits]

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@@ -125,6 +137,25 @@ class TypeDescriptor {
     return 1 << (TypeInfo >> 1);
   }
 
+  const char *getBitIntBitCountPointer() const {
+    DCHECK(isBitIntTy());
+    DCHECK(isSignedBitIntTy());
+    // Scan Name for zero and return the next address
+    const char *p = getTypeName();
+    while (*p != '\0')
+      ++p;
+    // Return the next address
+    return p + 1;
+  }
+
+  unsigned getIntegerBitCount() const {
+    DCHECK(isIntegerTy());
+    if (isSignedBitIntTy())
+      return *reinterpret_cast<const u32 *>(getBitIntBitCountPointer());
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jakubjelinek wrote:

This will not work on strict alignment targets.  I'd suggest instead of trying to reinterpret the bits memcpy them into u32 and return that, the compilers will optimize that properly.

https://github.com/llvm/llvm-project/pull/96240