[builtins] Fix signed shift overflows in ashlti3.c, ashrti3.c, ashldi3.c and ashrdi3.c

[Ka-Ka]

Summary

When compiling the builtins with the undefined behavior sanitizer and running testcases you end up with the following warning:

UBSan: ashlti3.c:33:35: left shift of 1 by 63 places cannot be represented in type 'di_int' (aka 'long long')
UBSan: ashrti3.c:34:34: left shift of negative value -81985529216486891

This can be avoided by doing the shift in a matching unsigned variant of the type.

The same kind of patterns are found in ashldi3.c and ashrdi3.c

This was found in an out of tree target.

[MaskRay]

Tested GCC __ashldi3 does silently discard high bits.

[Ka-Ka]

clang-format

compiler-rt/lib/builtins/ashldi3.c

COMPILER_RT_ABI di_int __ashldi3(di_int a, int b) {
   input.all = a;
   if (b & bits_in_word) /* bits_in_word <= b < bits_in_dword */ {
     result.s.low = 0;
     result.s.high = input.s.low << (b - bits_in_word);
   } else /* 0 <= b < bits_in_word */ {
     if (b == 0)
       return a;
     result.s.low = input.s.low << b;
-    result.s.high = (input.s.high << b) | (input.s.low >> (bits_in_word - b));
+    result.s.high =
+        ((su_int)input.s.high << b) | (input.s.low >> (bits_in_word - b));
   }
   return result.all;
 }
 
 #if defined(__ARM_EABI__)
 COMPILER_RT_ALIAS(__ashldi3, __aeabi_llsl)
 #endif

compiler-rt/lib/builtins/ashlti3.c

COMPILER_RT_ABI ti_int __ashlti3(ti_int a, int b) {
   input.all = a;
   if (b & bits_in_dword) /* bits_in_dword <= b < bits_in_tword */ {
     result.s.low = 0;
     result.s.high = input.s.low << (b - bits_in_dword);
   } else /* 0 <= b < bits_in_dword */ {
     if (b == 0)
       return a;
     result.s.low = input.s.low << b;
-    result.s.high = (input.s.high << b) | (input.s.low >> (bits_in_dword - b));
+    result.s.high =
+        ((du_int)input.s.high << b) | (input.s.low >> (bits_in_dword - b));
   }
   return result.all;
 }
 
 #endif // CRT_HAS_128BIT

compiler-rt/lib/builtins/ashrdi3.c

COMPILER_RT_ABI di_int __ashrdi3(di_int a, int b) {
   if (b & bits_in_word) /* bits_in_word <= b < bits_in_dword */ {
     // result.s.high = input.s.high < 0 ? -1 : 0
     result.s.high = input.s.high >> (bits_in_word - 1);
     result.s.low = input.s.high >> (b - bits_in_word);
   } else /* 0 <= b < bits_in_word */ {
     if (b == 0)
       return a;
     result.s.high = input.s.high >> b;
-    result.s.low = (input.s.high << (bits_in_word - b)) | (input.s.low >> b);
+    result.s.low =
+        ((su_int)input.s.high << (bits_in_word - b)) | (input.s.low >> b);
   }
   return result.all;
 }
 
 #if defined(__ARM_EABI__)
 COMPILER_RT_ALIAS(__ashrdi3, __aeabi_lasr)
 #endif

compiler-rt/lib/builtins/ashrti3.c

COMPILER_RT_ABI ti_int __ashrti3(ti_int a, int b) {
   if (b & bits_in_dword) /* bits_in_dword <= b < bits_in_tword */ {
     // result.s.high = input.s.high < 0 ? -1 : 0
     result.s.high = input.s.high >> (bits_in_dword - 1);
     result.s.low = input.s.high >> (b - bits_in_dword);
   } else /* 0 <= b < bits_in_dword */ {
     if (b == 0)
       return a;
     result.s.high = input.s.high >> b;
-    result.s.low = (input.s.high << (bits_in_dword - b)) | (input.s.low >> b);
+    result.s.low =
+        ((du_int)input.s.high << (bits_in_dword - b)) | (input.s.low >> b);
   }
   return result.all;
 }
 
 #endif // CRT_HAS_128BIT