[PATCH] D146623: [compiler-rt] Fix signed integer overflow in int_mulo_impl.inc

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

Ka-Ka created this revision.
Ka-Ka added reviewers: MaskRay, phosek, atrosinenko.
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When compiling compiler-rt with -fsanitize=undefined and running testcases you
end up with the following warning:

UBSan:/repo/uabkaka/llvm-project/compiler-rt/lib/builtins/int_mulo_impl.inc:24:23: signed integer overflow: -1 * -2147483648 cannot be represented in type 'si_int' (aka 'long')

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

This was found in an out of tree target.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146623

Files:
  compiler-rt/lib/builtins/int_mulo_impl.inc


Index: compiler-rt/lib/builtins/int_mulo_impl.inc
===================================================================
--- compiler-rt/lib/builtins/int_mulo_impl.inc
+++ compiler-rt/lib/builtins/int_mulo_impl.inc
@@ -21,7 +21,7 @@
   const fixint_t MIN = (fixint_t)((fixuint_t)1 << (N - 1));
   const fixint_t MAX = ~MIN;
   *overflow = 0;
-  fixint_t result = a * b;
+  fixint_t result = (fixuint_t)a * b;
   if (a == MIN) {
     if (b != 0 && b != 1)
       *overflow = 1;


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