Fixes codegen bug with literal negative zero, fixes #7079 (#7158)

* Fixes #7079

* Fix handling of neg zero during constant folding

compiler/jsgen.nim

@@ -2284,11 +2284,17 @@ proc gen(p: PProc, n: PNode, r: var TCompRes) =
     r.kind = resExpr
   of nkFloatLit..nkFloat64Lit:
     let f = n.floatVal
-    if f != f: r.res = rope"NaN"
-    elif f == 0.0: r.res = rope"0.0"
-    elif f == 0.5 * f:
-      if f > 0.0: r.res = rope"Infinity"
-      else: r.res = rope"-Infinity"
+    case classify(f)
+    of fcNaN:
+      r.res = rope"NaN"
+    of fcNegZero:
+      r.res = rope"-0.0"
+    of fcZero:
+      r.res = rope"0.0"
+    of fcInf:
+      r.res = rope"Infinity"
+    of fcNegInf:
+      r.res = rope"-Infinity"
     else: r.res = rope(f.toStrMaxPrecision)
     r.kind = resExpr
   of nkCallKinds:

compiler/rodutils.nim

@@ -8,18 +8,22 @@
 #
 
 ## Serialization utilities for the compiler.
-import strutils
+import strutils, math
 
 proc c_snprintf(s: cstring; n:uint; frmt: cstring): cint {.importc: "snprintf", header: "<stdio.h>", nodecl, varargs.}
 
 proc toStrMaxPrecision*(f: BiggestFloat, literalPostfix = ""): string =
-  if f != f:
+  case classify(f)
+  of fcNaN:
     result = "NAN"
-  elif f == 0.0:
+  of fcNegZero:
+    result = "-0.0" & literalPostfix
+  of fcZero:
     result = "0.0" & literalPostfix
-  elif f == 0.5 * f:
-    if f > 0.0: result = "INF"
-    else: result = "-INF"
+  of fcInf:
+    result = "INF"
+  of fcNegInf:
+    result = "-INF"
   else:
     when defined(nimNoArrayToCstringConversion):
       result = newString(81)

compiler/semfold.nim

@@ -225,6 +225,7 @@ proc evalOp(m: TMagic, n, a, b, c: PNode): PNode =
   of mDivF64:
     if getFloat(b) == 0.0:
       if getFloat(a) == 0.0: result = newFloatNodeT(NaN, n)
+      elif getFloat(b).classify == fcNegZero: result = newFloatNodeT(-Inf, n)
       else: result = newFloatNodeT(Inf, n)
     else:
       result = newFloatNodeT(getFloat(a) / getFloat(b), n)

tests/ccgbugs/t7079.nim

@@ -0,0 +1,9 @@
+discard """
+  action: run
+  targets: '''c js'''
+"""
+
+import math
+let x = -0.0
+doAssert classify(x) == fcNegZero
+doAssert classify(1 / -0.0) == fcNegInf