stage2: fix comptime bitcast involving f80

* Sema: implement comptime bitcast of f80 with integer-like types
  bitwise rather than taking a round trip through memory layout.
* Type: introduce `isAbiInt`.
* Value: comptime memory write of f80 writes 0 bytes for padding
  instead of leaving the memory uninitialized.
* Value: floatReadFromMemory has a more general implementation, checking
  the endianness rather than checking for specific architectures.

This fixes behavior test failures occurring on MIPS.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/type.zig b/src/type.zig
index 765f1da18c..0744a50579 100644
--- a/src/type.zig
+++ b/src/type.zig
@@ -4439,6 +4439,16 @@ pub const Type = extern union {
         };
     }
 
+    /// Returns true for integers, enums, error sets, and packed structs.
+    /// If this function returns true, then intInfo() can be called on the type.
+    pub fn isAbiInt(ty: Type) bool {
+        return switch (ty.zigTypeTag()) {
+            .Int, .Enum, .ErrorSet => true,
+            .Struct => ty.containerLayout() == .Packed,
+            else => false,
+        };
+    }
+
     /// Asserts the type is an integer, enum, error set, or vector of one of them.
     pub fn intInfo(self: Type, target: Target) struct { signedness: std.builtin.Signedness, bits: u16 } {
         var ty = self;