[X86] Support EVEX compression from MOVBErr to BSWAP (#79775)

APX promoted MOVBE instructions were supported in #77431. The reg2reg
variants of MOVBE are newly introduced by APX and can be optimized to
BSWAP instruction when the 2 register operands are same.

This patch adds manual entries for MOVBErr instructions when we do ndd
to non-ndd compression #77731.
RFC:
https://discourse.llvm.org/t/rfc-design-for-apx-feature-egpr-and-ndd-support/73031/4

llvm/lib/Target/X86/X86CompressEVEX.cpp

@@ -225,9 +225,12 @@ static bool CompressEVEXImpl(MachineInstr &MI, const X86Subtarget &ST) {
   //
   // For AVX512 cases, EVEX prefix is needed in order to carry this information
   // thus preventing the transformation to VEX encoding.
+  // MOVBE*rr is special because it has semantic of NDD but not set EVEX_B.
+  bool IsMovberr =
+      MI.getOpcode() == X86::MOVBE32rr || MI.getOpcode() == X86::MOVBE64rr;
   bool IsND = X86II::hasNewDataDest(TSFlags);
-  if (TSFlags & X86II::EVEX_B)
-    if (!IsND || !isRedundantNewDataDest(MI, ST))
+  if ((TSFlags & X86II::EVEX_B) || IsMovberr)
+    if (!IsND && !IsMovberr || !isRedundantNewDataDest(MI, ST))
       return false;
 
   ArrayRef<X86CompressEVEXTableEntry> Table = ArrayRef(X86CompressEVEXTable);
@@ -239,7 +242,7 @@ static bool CompressEVEXImpl(MachineInstr &MI, const X86Subtarget &ST) {
     return false;
   }
 
-  if (!IsND) {
+  if (!IsND && !IsMovberr) {
     if (usesExtendedRegister(MI) || !checkPredicate(I->NewOpc, &ST) ||
         !performCustomAdjustments(MI, I->NewOpc))
       return false;

llvm/test/CodeGen/X86/apx/compress-evex.mir

@@ -71,3 +71,13 @@ body:             |
     renamable $rax = XOR64rr_NF_ND killed renamable $rax, killed renamable $r16
     RET64 $rax
 ...
+---
+name:            bswapr_to_movberr
+body:             |
+  bb.0.entry:
+    liveins: $rax
+    ; CHECK: bswapq  %rax                            # EVEX TO LEGACY Compression encoding: [0x48,0x0f,0xc8]
+    renamable $rax = MOVBE64rr killed renamable $rax
+    RET64 killed $rax
+
+...

llvm/utils/TableGen/X86ManualCompressEVEXTables.def

@@ -328,4 +328,6 @@ ENTRY(VBROADCASTSDZ256rm, VBROADCASTSDYrm)
 ENTRY(VBROADCASTSDZ256rr, VBROADCASTSDYrr)
 ENTRY(VPBROADCASTQZ256rm, VPBROADCASTQYrm)
 ENTRY(VPBROADCASTQZ256rr, VPBROADCASTQYrr)
+ENTRY(MOVBE32rr, BSWAP32r)
+ENTRY(MOVBE64rr, BSWAP64r)
 #undef ENTRY