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

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.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D158819

compiler-rt/lib/builtins/ashldi3.c

@@ -28,7 +28,8 @@ COMPILER_RT_ABI di_int __ashldi3(di_int a, int b) {
     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;
 }

compiler-rt/lib/builtins/ashlti3.c

@@ -30,7 +30,8 @@ COMPILER_RT_ABI ti_int __ashlti3(ti_int a, int b) {
     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;
 }

compiler-rt/lib/builtins/ashrdi3.c

@@ -29,7 +29,8 @@ COMPILER_RT_ABI di_int __ashrdi3(di_int a, int b) {
     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;
 }

compiler-rt/lib/builtins/ashrti3.c

@@ -31,7 +31,8 @@ COMPILER_RT_ABI ti_int __ashrti3(ti_int a, int b) {
     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;
 }