[PATCH] D158818: [builtins] Fix undefined behavior in negdi2.c and negti2.c

[Karl-Johan Karlsson via Phabricator via llvm-commits]

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

UBSan: negdi2.c:20:10: negation of -9223372036854775808 cannot be represented in type 'di_int' (aka 'long long'); cast to an unsigned type to negate this value to itself

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

The same kind of pattern is found in negti2.c

This was found in an out of tree target.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158818

Files:
  compiler-rt/lib/builtins/negdi2.c
  compiler-rt/lib/builtins/negti2.c


Index: compiler-rt/lib/builtins/negti2.c
===================================================================
--- compiler-rt/lib/builtins/negti2.c
+++ compiler-rt/lib/builtins/negti2.c
@@ -19,7 +19,7 @@
 COMPILER_RT_ABI ti_int __negti2(ti_int a) {
   // Note: this routine is here for API compatibility; any sane compiler
   // should expand it inline.
-  return -a;
+  return -(tu_int)a;
 }
 
 #endif // CRT_HAS_128BIT
Index: compiler-rt/lib/builtins/negdi2.c
===================================================================
--- compiler-rt/lib/builtins/negdi2.c
+++ compiler-rt/lib/builtins/negdi2.c
@@ -17,5 +17,5 @@
 COMPILER_RT_ABI di_int __negdi2(di_int a) {
   // Note: this routine is here for API compatibility; any sane compiler
   // should expand it inline.
-  return -a;
+  return -(du_int)a;
 }


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