x64: Elide more uextend with extractlane (#6045)

* x64: Elide more uextend with extractlane

I've confirmed locally now that `pextr{b,w,d}` all zero the upper bits
of the full 64-bit register size which means that the `extractlane`
operation with a zero-extend can be elided for more cases, including
8-to-64-bit casts as well as 32-to-64.

This helps elide a few extra `mov`s in a loop I was looking at and had a
modest corresponding increase in performance (my guess was due to the
slightly decreased code size mostly as opposed to the removed `mov`s).

* Remove stray file

cranelift/codegen/src/isa/x64/inst.isle

@@ -1715,14 +1715,11 @@
         (if-let $true (value32_zeros_upper32 src))
         src)
 
-;; The `extractlane` instruction, extended to `$I32`, means that either an
+;; The `extractlane` instruction, when paired with a zero-extension, means
-;; i8x16 or an i16x8 is being extracted. These are implemented with
+;; that one of `i{8x16,16x8,32x4}` is being extracted and extend. These
-;; the `pextr{b,w}` instruction which automatically zero the upper bits of the
+;; extractions are implemented with the `pextr{b,w,d}` instructions which
-;; destination register so the `uextend` in these cases can be elided.
+;; automatically zero the upper bits of the destination register so the
-;;
+;; `uextend` in these cases can be elided.
-;; TODO: the documentation for `pextr{b,w}` seems to indicate it zero extends
-;; to not only 32-bits but probably the whole 64-bit register. If that's the
-;; case then this should match a zero-extend to any size instead of just `$I32`.
 ;;
 ;; TODO: the interaction here between this rule and the "it's written far away"
 ;; rule to lower `extractlane` isn't great. Ideally this rule (and the other
@@ -1730,7 +1727,7 @@
 ;; be connected to the extractlane rules. There's some discussion of this on
 ;; #6022 but the gist is that there's not a lot of great options at this time,
 ;; so this doc block is what's here for now.
-(rule 1 (extend_to_gpr src @ (extractlane _ _) $I32 (ExtendKind.Zero))
+(rule 1 (extend_to_gpr src @ (extractlane _ _) _ (ExtendKind.Zero))
         src)
 
 (rule (extend_to_gpr (and val (value_type from_ty))

cranelift/codegen/src/isa/x64/lower.isle

@@ -3808,6 +3808,8 @@
 (rule 0 (lower (extractlane val @ (value_type ty @ (multi_lane 16 8)) (u8_from_uimm8 lane)))
       (x64_pextrw val lane))
 
+;; See the note in the 8x16 case above for how this rule is connected to
+;; `extend_to_gpr`.
 (rule 0 (lower (extractlane val @ (value_type ty @ (multi_lane 32 4)) (u8_from_uimm8 lane)))
       (x64_pextrd val lane))
 

cranelift/filetests/filetests/isa/x64/uextend-elision.clif

@@ -79,6 +79,32 @@ block0(v0: i8x16):
 ;   popq %rbp
 ;   retq
 
+function %extractlane_i8x16_i64(i8x16) -> i64 {
+block0(v0: i8x16):
+    v1 = extractlane v0, 1
+    v2 = uextend.i64 v1
+    return v2
+}
+
+; VCode:
+;   pushq   %rbp
+;   movq    %rsp, %rbp
+; block0:
+;   pextrb  $1, %xmm0, %rax
+;   movq    %rbp, %rsp
+;   popq    %rbp
+;   ret
+; 
+; Disassembled:
+; block0: ; offset 0x0
+;   pushq %rbp
+;   movq %rsp, %rbp
+; block1: ; offset 0x4
+;   pextrb $1, %xmm0, %eax
+;   movq %rbp, %rsp
+;   popq %rbp
+;   retq
+
 function %extractlane_i16x8_i32(i16x8) -> i32 {
 block0(v0: i16x8):
     v1 = extractlane v0, 1
@@ -105,3 +131,55 @@ block0(v0: i16x8):
 ;   popq %rbp
 ;   retq
 
+function %extractlane_i16x8_i64(i16x8) -> i64 {
+block0(v0: i16x8):
+    v1 = extractlane v0, 1
+    v2 = uextend.i64 v1
+    return v2
+}
+
+; VCode:
+;   pushq   %rbp
+;   movq    %rsp, %rbp
+; block0:
+;   pextrw  $1, %xmm0, %rax
+;   movq    %rbp, %rsp
+;   popq    %rbp
+;   ret
+; 
+; Disassembled:
+; block0: ; offset 0x0
+;   pushq %rbp
+;   movq %rsp, %rbp
+; block1: ; offset 0x4
+;   pextrw $1, %xmm0, %eax
+;   movq %rbp, %rsp
+;   popq %rbp
+;   retq
+
+function %extractlane_i32x4_i64(i32x4) -> i64 {
+block0(v0: i32x4):
+    v1 = extractlane v0, 1
+    v2 = uextend.i64 v1
+    return v2
+}
+
+; VCode:
+;   pushq   %rbp
+;   movq    %rsp, %rbp
+; block0:
+;   pextrd  $1, %xmm0, %rax
+;   movq    %rbp, %rsp
+;   popq    %rbp
+;   ret
+; 
+; Disassembled:
+; block0: ; offset 0x0
+;   pushq %rbp
+;   movq %rsp, %rbp
+; block1: ; offset 0x4
+;   pextrd $1, %xmm0, %eax
+;   movq %rbp, %rsp
+;   popq %rbp
+;   retq
+