[clang] [C2y] Add conformance test for WG14 N3364 (PR #115332)

[Erich Keane via cfe-commits]

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@@ -0,0 +1,35 @@
+// RUN: %clang_cc1 -verify -std=c2y -Wall -pedantic -emit-llvm -o - %s
+// RUN: %clang_cc1 -verify -Wall -pedantic -emit-llvm -o - %s
+// expected-no-diagnostics
+
+/* WG14 N3364: Yes
+ * Give consistent wording for SNAN initialization v3
+ *
+ * Ensure that initializing from a signaling NAN (optionally with a unary + or
+ * -) at translation time behaves correctly at runtime.
+ */
+
+#define FLT_SNAN __builtin_nansf("1")
+#define DBL_SNAN __builtin_nans("1")
+#define LD_SNAN __builtin_nansl("1")
+
+float f1 = FLT_SNAN;
+float f2 = +FLT_SNAN;
+float f3 = -FLT_SNAN;
+// CHECK: @f1 = {{.*}}global float 0x7FF0000020000000
+// CHECK: @f2 = {{.*}}global float 0x7FF0000020000000
+// CHECK: @f3 = {{.*}}global float 0xFFF0000020000000
+
+double d1 = DBL_SNAN;
+double d2 = +DBL_SNAN;
+double d3 = -DBL_SNAN;
+// CHECK: @d1 = {{.*}}global double 0x7FF0000000000001
+// CHECK: @d2 = {{.*}}global double 0x7FF0000000000001
+// CHECK: @d3 = {{.*}}global double 0xFFF0000000000001
+
+long double ld1 = LD_SNAN;
+long double ld2 = +LD_SNAN;
+long double ld3 = -LD_SNAN;
+// CHECK: @ld1 = {{.*}}global {{double 0x7FF0000000000001|x86_fp80 0xK7FFF8000000000000001|fp128 0xL00000000000000017FFF000000000000}}
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erichkeane wrote:

@jcranmer-intel : I recall seeing in the past that we sometimes print floats as scientific notation.  Is this/the above in danger in any way because of it?

https://github.com/llvm/llvm-project/pull/115332