[compiler-rt] Fix signed shift overflows in absvdi2.c, absvsi2.c, negvdi2.c and negvsi2.c

[Ka-Ka]

Summary

When compiling compiler-rt with -fsanitize=undefined and running testcases you
end up with the following warnings:

UBSan: absvdi2.c:21:23: left shift of 1 by 63 places cannot be represented in type 'di_int' (aka 'long long')
UBSan: absvsi2.c:21:23: left shift of 1 by 31 places cannot be represented in type 'si_int' (aka 'long')
UBSan: negvdi2.c:20:32: left shift of 1 by 63 places cannot be represented in type 'di_int' (aka 'long long')
UBSan: negvsi2.c:20:32: left shift of 1 by 31 places cannot be represented in type 'si_int' (aka 'long')

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

This was found in an out of tree target.

[Ka-Ka]

git-clang-format

compiler-rt/lib/builtins/absvdi2.c

 #include "int_lib.h"
 
 // Returns: absolute value
 
 // Effects: aborts if abs(x) < 0
 
 COMPILER_RT_ABI di_int __absvdi2(di_int a) {
   const int N = (int)(sizeof(di_int) * CHAR_BIT);
-  if (a == ((di_int)1 << (N - 1)))
+  if (a == ((di_int)((du_int)1 << (N - 1))))
     compilerrt_abort();
   const di_int t = a >> (N - 1);
   return (a ^ t) - t;
 }

compiler-rt/lib/builtins/absvsi2.c

 #include "int_lib.h"
 
 // Returns: absolute value
 
 // Effects: aborts if abs(x) < 0
 
 COMPILER_RT_ABI si_int __absvsi2(si_int a) {
   const int N = (int)(sizeof(si_int) * CHAR_BIT);
-  if (a == ((si_int)1 << (N - 1)))
+  if (a == ((si_int)((su_int)1 << (N - 1))))
     compilerrt_abort();
   const si_int t = a >> (N - 1);
   return (a ^ t) - t;
 }

compiler-rt/lib/builtins/negvdi2.c

 
 #include "int_lib.h"
 
 // Returns: -a
 
 // Effects: aborts if -a overflows
 
 COMPILER_RT_ABI di_int __negvdi2(di_int a) {
-  const di_int MIN = (di_int)1 << ((int)(sizeof(di_int) * CHAR_BIT) - 1);
+  const di_int MIN =
+      (di_int)((du_int)1 << ((int)(sizeof(di_int) * CHAR_BIT) - 1));
   if (a == MIN)
     compilerrt_abort();
   return -a;
 }

compiler-rt/lib/builtins/negvsi2.c

 
 #include "int_lib.h"
 
 // Returns: -a
 
 // Effects: aborts if -a overflows
 
 COMPILER_RT_ABI si_int __negvsi2(si_int a) {
-  const si_int MIN = (si_int)1 << ((int)(sizeof(si_int) * CHAR_BIT) - 1);
+  const si_int MIN =
+      (si_int)((su_int)1 << ((int)(sizeof(si_int) * CHAR_BIT) - 1));
   if (a == MIN)
     compilerrt_abort();
   return -a;
 }