Fix #22489 - e - e is not 0 with NaNs

Author: limepoutine

compiler/src/dmd/backend/cgelem.d

@@ -1226,7 +1226,7 @@ private elem* elmin(elem* e, Goal goal)
         }
 
         // Replace (e - e) with (0)
-        if (el_match(e1,e2) && !el_sideeffect(e1))
+        if (el_match(e1,e2) && !el_sideeffect(e1) && !tyfloating(tym))
         {
             el_free(e);
             e = el_calloc();

compiler/test/runnable/test22489.d

@@ -0,0 +1,31 @@
+/*
+REQUIRED_ARGS: -inline -O
+RUN_OUTPUT:
+---
+32767
+32767
+---
+*/
+
+enum ushort EXPMASK = 0x7FFF;
+
+version (LittleEndian)
+    enum EXPPOS_SHORT = 4;
+else
+    enum EXPPOS_SHORT = 0;
+
+int getExp(real x, real y)
+{
+    real diff = x - y;
+    ushort* pa = cast(ushort*)(&x);
+    ushort* pb = cast(ushort*)(&y);
+    ushort* pd = cast(ushort*)(&diff);
+    return pd[EXPPOS_SHORT] & EXPMASK;
+}
+
+void main()
+{
+    import core.stdc.stdio;
+    printf("%d\n", getExp(real.nan, real.nan));
+    printf("%d\n", getExp(real.nan, real.nan));
+}