llvm codegen: fix f16,f32,f64 nan bitcasts

@bitcast from integer NaN representation to float NaN resulted in
changed bits in float. This only happened with signaled NaN.

- added test for signaled NaN
- added tests for quiet NaN (for completeness)

closes #14198

Author: mikdusan

src/codegen/llvm.zig

@@ -3287,15 +3287,24 @@ pub const DeclGen = struct {
             .Float => {
                 const llvm_ty = try dg.lowerType(tv.ty);
                 switch (tv.ty.floatBits(target)) {
-                    16 => if (intrinsicsAllowed(tv.ty, target)) {
-                        return llvm_ty.constReal(tv.val.toFloat(f16));
-                    } else {
+                    16 => {
                         const repr = @bitCast(u16, tv.val.toFloat(f16));
                         const llvm_i16 = dg.context.intType(16);
                         const int = llvm_i16.constInt(repr, .False);
                         return int.constBitCast(llvm_ty);
                     },
-                    32, 64 => return llvm_ty.constReal(tv.val.toFloat(f64)),
+                    32 => {
+                        const repr = @bitCast(u32, tv.val.toFloat(f32));
+                        const llvm_i32 = dg.context.intType(32);
+                        const int = llvm_i32.constInt(repr, .False);
+                        return int.constBitCast(llvm_ty);
+                    },
+                    64 => {
+                        const repr = @bitCast(u64, tv.val.toFloat(f64));
+                        const llvm_i64 = dg.context.intType(64);
+                        const int = llvm_i64.constInt(repr, .False);
+                        return int.constBitCast(llvm_ty);
+                    },
                     80 => {
                         const float = tv.val.toFloat(f80);
                         const repr = std.math.break_f80(float);

test/behavior.zig

@@ -241,6 +241,7 @@ test {
     {
         _ = @import("behavior/bugs/13063.zig");
         _ = @import("behavior/bugs/11227.zig");
+        _ = @import("behavior/bugs/14198.zig");
         _ = @import("behavior/export.zig");
     }
 

test/behavior/bugs/14198.zig

@@ -0,0 +1,18 @@
+const std = @import("std");
+const math = std.math;
+const mem = std.mem;
+const testing = std.testing;
+
+test "nan memory equality" {
+    // signaled
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.nan_u16), mem.asBytes(&math.nan_f16)));
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.nan_u32), mem.asBytes(&math.nan_f32)));
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.nan_u64), mem.asBytes(&math.nan_f64)));
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.nan_u128), mem.asBytes(&math.nan_f128)));
+
+    // quiet
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.qnan_u16), mem.asBytes(&math.qnan_f16)));
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.qnan_u32), mem.asBytes(&math.qnan_f32)));
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.qnan_u64), mem.asBytes(&math.qnan_f64)));
+    try testing.expect(mem.eql(u8, mem.asBytes(&math.qnan_u128), mem.asBytes(&math.qnan_f128)));
+}