fix -IV_MIN negations

Doing uv = -iv is undefined behaviour if iv happens to be IV_MIN.
This occurs in several places in the perl sources.

Found by -fsanitize=undefined.

Here's a typical message:

sv.c:2864:7: runtime error: negation of -9223372036854775808 cannot be represented in type 'IV' (aka 'long'); cast to an unsigned type to negate this value to itself

3 files changed, 21 insertions, 14 deletions

diff --git a/pp.c b/pp.c
index 08e0999f3e..e24b5714fe 100644
--- a/pp.c
+++ b/pp.c
@@ -1298,7 +1298,8 @@ PP(pp_multiply)
 		    alow = aiv;
 		    auvok = TRUE; /* effectively it's a UV now */
 		} else {
-		    alow = -aiv; /* abs, auvok == false records sign */
+                    /* abs, auvok == false records sign */
+		    alow = (aiv == IV_MIN) ? (UV)aiv : (UV)(-aiv);
 		}
 	    }
 	    if (buvok) {
@@ -1309,7 +1310,8 @@ PP(pp_multiply)
 		    blow = biv;
 		    buvok = TRUE; /* effectively it's a UV now */
 		} else {
-		    blow = -biv; /* abs, buvok == false records sign */
+                    /* abs, buvok == false records sign */
+		    blow = (biv == IV_MIN) ? (UV)biv : (UV)(-biv);
 		}
 	    }
 
@@ -1372,7 +1374,8 @@ PP(pp_multiply)
 			    /* 2s complement assumption again  */
 			    /* -ve result, which could overflow an IV  */
 			    SP--;
-			    SETi( -(IV)product_low );
+			    SETi(product_low == (UV)IV_MIN
+                                    ? IV_MIN : -(IV)product_low);
 			    RETURN;
 			} /* else drop to NVs below. */
 		    }
@@ -1797,7 +1800,7 @@ PP(pp_subtract)
 			auv = aiv;
 			auvok = 1;	/* Now acting as a sign flag.  */
 		    } else { /* 2s complement assumption for IV_MIN */
-			auv = (UV)-aiv;
+			auv = (aiv == IV_MIN) ? (UV)aiv : (UV)-aiv;
 		    }
 		}
 		a_valid = 1;
@@ -1817,7 +1820,7 @@ PP(pp_subtract)
 		    buv = biv;
 		    buvok = 1;
 		} else
-		    buv = (UV)-biv;
+                    buv = (biv == IV_MIN) ? (UV)biv : (UV)-biv;
 	    }
 	    /* ?uvok if value is >= 0. basically, flagged as UV if it's +ve,
 	       else "IV" now, independent of how it came in.
@@ -1858,7 +1861,8 @@ PP(pp_subtract)
 		else {
 		    /* Negate result */
 		    if (result <= (UV)IV_MIN)
-			SETi( -(IV)result );
+                        SETi(result == (UV)IV_MIN
+                                ? IV_MIN : -(IV)result);
 		    else {
 			/* result valid, but out of range for IV.  */
 			SETn( -(NV)result );
diff --git a/pp_hot.c b/pp_hot.c
index 3ee48180d3..4072ab11e1 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -647,8 +647,8 @@ PP(pp_add)
 		    if (aiv >= 0) {
 			auv = aiv;
 			auvok = 1;	/* Now acting as a sign flag.  */
-		    } else { /* 2s complement assumption for IV_MIN */
-			auv = (UV)-aiv;
+		    } else {
+			auv = (aiv == IV_MIN) ? (UV)aiv : (UV)(-aiv);
 		    }
 		}
 		a_valid = 1;
@@ -668,7 +668,7 @@ PP(pp_add)
 		    buv = biv;
 		    buvok = 1;
 		} else
-		    buv = (UV)-biv;
+                    buv = (biv == IV_MIN) ? (UV)biv : (UV)(-biv);
 	    }
 	    /* ?uvok if value is >= 0. basically, flagged as UV if it's +ve,
 	       else "IV" now, independent of how it came in.
@@ -709,7 +709,8 @@ PP(pp_add)
 		else {
 		    /* Negate result */
 		    if (result <= (UV)IV_MIN)
-			SETi( -(IV)result );
+                        SETi(result == (UV)IV_MIN
+                                ? IV_MIN : -(IV)result);
 		    else {
 			/* result valid, but out of range for IV.  */
 			SETn( -(NV)result );
diff --git a/sv.c b/sv.c
index 94740d3528..f33da0b5e9 100644
--- a/sv.c
+++ b/sv.c
@@ -2158,6 +2158,7 @@ S_sv_2iuv_common(pTHX_ SV *const sv)
 	    SvIV_set(sv, I_V(SvNVX(sv)));
 	    if (SvNVX(sv) == (NV) SvIVX(sv)
 #ifndef NV_PRESERVES_UV
+                && SvIVX(sv) != IV_MIN /* avoid negating IV_MIN below */
 		&& (((UV)1 << NV_PRESERVES_UV_BITS) >
 		    (UV)(SvIVX(sv) > 0 ? SvIVX(sv) : -SvIVX(sv)))
 		/* Don't flag it as "accurately an integer" if the number
@@ -2273,7 +2274,8 @@ S_sv_2iuv_common(pTHX_ SV *const sv)
 	    } else {
 		/* 2s complement assumption  */
 		if (value <= (UV)IV_MIN) {
-		    SvIV_set(sv, -(IV)value);
+		    SvIV_set(sv, value == (UV)IV_MIN
+                                    ? IV_MIN : -(IV)value);
 		} else {
 		    /* Too negative for an IV.  This is a double upgrade, but
 		       I'm assuming it will be rare.  */
@@ -2732,7 +2734,7 @@ Perl_sv_2nv_flags(pTHX_ SV *const sv, const I32 flags)
             SvNOK_on(sv);
         } else {
             /* value has been set.  It may not be precise.  */
-	    if ((numtype & IS_NUMBER_NEG) && (value > (UV)IV_MIN)) {
+	    if ((numtype & IS_NUMBER_NEG) && (value >= (UV)IV_MIN)) {
 		/* 2s complement assumption for (UV)IV_MIN  */
                 SvNOK_on(sv); /* Integer is too negative.  */
             } else {
@@ -2861,7 +2863,7 @@ S_uiv_2buf(char *const buf, const IV iv, UV uv, const int is_uv, char **const pe
 	uv = iv;
 	sign = 0;
     } else {
-	uv = -iv;
+        uv = (iv == IV_MIN) ? (UV)iv : (UV)(-iv);
 	sign = 1;
     }
     do {
@@ -11898,7 +11900,7 @@ Perl_sv_vcatpvfn_flags(pTHX_ SV *const sv, const char *const pat, const STRLEN p
 			esignbuf[esignlen++] = plus;
 		}
 		else {
-		    uv = -iv;
+		    uv = (iv == IV_MIN) ? (UV)iv : (UV)(-iv);
 		    esignbuf[esignlen++] = '-';
 		}
 	    }