[X86] Add an isel pattern for (i8 (trunc (i16 (bitconvert (v16i1 X))))) to avoid...

Since we can only copy to GR32 we had to EXTRACT from GR32, but
we would first go to GR16 and then the truncate would extra again
to GR8. This adds a special case to go directly from GR32 to GR8.
This would eventually get cleaned up, but though maybe we should
avoid doing it in the first place. Our k-register handling is weird
and we could probably stand to have some more special ISD nodes
for the conversions so the i32 type would be explicit.

diff --git a/llvm/lib/Target/X86/X86InstrAVX512.td b/llvm/lib/Target/X86/X86InstrAVX512.td
index 0514a3a..e1eb664 100644 (file)
--- a/llvm/lib/Target/X86/X86InstrAVX512.td
+++ b/llvm/lib/Target/X86/X86InstrAVX512.td
@@ -2884,6 +2884,8 @@ def : Pat<(v16i1 (bitconvert (i16 GR16:$src))),
           (COPY_TO_REGCLASS (i32 (INSERT_SUBREG (IMPLICIT_DEF), GR16:$src, sub_16bit)), VK16)>;
 def : Pat<(i16 (bitconvert (v16i1 VK16:$src))),
           (EXTRACT_SUBREG (i32 (COPY_TO_REGCLASS VK16:$src, GR32)), sub_16bit)>;
+def : Pat<(i8 (trunc (i16 (bitconvert (v16i1 VK16:$src))))),
+          (EXTRACT_SUBREG (i32 (COPY_TO_REGCLASS VK16:$src, GR32)), sub_8bit)>;
 
 def : Pat<(v8i1 (bitconvert (i8 GR8:$src))),
           (COPY_TO_REGCLASS (i32 (INSERT_SUBREG (IMPLICIT_DEF), GR8:$src, sub_8bit)), VK8)>;