[committed] libgcc: Avoid signed negation overflow in __powi?f2 [PR99236]

[Jakub Jelinek via Gcc-patches]

Hi!

When these functions are called with integer minimum, there is UB on the libgcc
side.  Fixed in the obvious way, the code in the end wants ABSU_EXPR behavior.

Bootstrapped/regtested on x86_64-linux and i686-linux, committed to trunk
as obvious.

2021-02-24  Jakub Jelinek  <ja...@redhat.com>

        PR libgcc/99236
        * libgcc2.c (__powisf2, __powidf2, __powitf2, __powixf2): Perform
        negation of m in unsigned type.

--- libgcc/libgcc2.c.jj 2021-01-04 10:25:53.727065175 +0100
+++ libgcc/libgcc2.c    2021-02-24 13:33:38.415470027 +0100
@@ -1834,7 +1834,7 @@ __fixunssfSI (SFtype a)
 TYPE
 NAME (TYPE x, int m)
 {
-  unsigned int n = m < 0 ? -m : m;
+  unsigned int n = m < 0 ? -(unsigned int) m : (unsigned int) m;
   TYPE y = n % 2 ? x : 1;
   while (n >>= 1)
     {


        Jakub