x64: Remove conditional SseOpcode::uses_src1 (#5842)

This is a follow-up to comments in #5795 to remove some cruft in the x64
instruction model to ensure that the shape of an `Inst` reflects what's
going to happen in regalloc and encoding. This accessor was used to
handle `round*`, `pextr*`, and `pshufb` instructions. The `round*` ones
had already moved to the appropriate `XmmUnary*` variant and `pshufb`
was additionally moved over to that variant as well.

The `pextr*` instructions got a new `Inst` variant and additionally had
their constructors slightly modified to no longer require the type as
input. The encoding for these instructions now automatically handles the
various type-related operands through a new `SseOpcode::Pextrq` operand
to represent 64-bit movements.

cranelift/codegen/src/isa/x64/inst/args.rs

@@ -999,6 +999,7 @@ pub enum SseOpcode {
     Pextrb,
     Pextrw,
     Pextrd,
+    Pextrq,
     Pinsrb,
     Pinsrw,
     Pinsrd,
@@ -1237,6 +1238,7 @@ impl SseOpcode {
             | SseOpcode::Pcmpeqq
             | SseOpcode::Pextrb
             | SseOpcode::Pextrd
+            | SseOpcode::Pextrq
             | SseOpcode::Pinsrb
             | SseOpcode::Pinsrd
             | SseOpcode::Pmaxsb
@@ -1278,22 +1280,6 @@ impl SseOpcode {
             _ => 8,
         }
     }
-
-    /// Does an XmmRmmRImm with this opcode use src1? FIXME: split
-    /// into separate instructions.
-    pub(crate) fn uses_src1(&self) -> bool {
-        match self {
-            SseOpcode::Pextrb => false,
-            SseOpcode::Pextrw => false,
-            SseOpcode::Pextrd => false,
-            SseOpcode::Pshufd => false,
-            SseOpcode::Roundss => false,
-            SseOpcode::Roundsd => false,
-            SseOpcode::Roundps => false,
-            SseOpcode::Roundpd => false,
-            _ => true,
-        }
-    }
 }
 
 impl fmt::Debug for SseOpcode {
@@ -1393,6 +1379,7 @@ impl fmt::Debug for SseOpcode {
             SseOpcode::Pextrb => "pextrb",
             SseOpcode::Pextrw => "pextrw",
             SseOpcode::Pextrd => "pextrd",
+            SseOpcode::Pextrq => "pextrq",
             SseOpcode::Pinsrb => "pinsrb",
             SseOpcode::Pinsrw => "pinsrw",
             SseOpcode::Pinsrd => "pinsrd",