[llvm] [AMDGPU] Select v_bfe_u32 for i8/i16 (and (srl x, c), mask) (PR #182446)

[Matt Arsenault via llvm-commits]

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@@ -4157,17 +4157,32 @@ def IMMZeroBasedBitfieldMask : ImmLeaf <i32, [{
   return isMask_32(Imm);
 }]>;
 
+def IMMZeroBasedBitfieldMask16 : ImmLeaf <i16, [{
+  return isUInt<16>(Imm) && isMask_32(Imm);
+}]>;
+
 def IMMPopCount : SDNodeXForm<imm, [{
   return CurDAG->getTargetConstant(llvm::popcount(N->getZExtValue()), SDLoc(N),
                                    MVT::i32);
 }]>;
 
+def IMMAsI32 : SDNodeXForm<imm, [{
+  return CurDAG->getTargetConstant(N->getZExtValue(), SDLoc(N), MVT::i32);
+}]>;
+
 def : AMDGPUPat <
   (DivergentBinFrag<and> (i32 (srl i32:$src, i32:$rshift)),
                          IMMZeroBasedBitfieldMask:$mask),
   (V_BFE_U32_e64 $src, $rshift, (i32 (IMMPopCount $mask)))
 >;
 
+let True16Predicate = NotUseRealTrue16Insts in
+def : AMDGPUPat <
+  (i16 (DivergentBinFrag<and> (srl_oneuse i16:$src, (i16 imm:$rshift)),
+                              IMMZeroBasedBitfieldMask16:$mask)),
+  (V_BFE_U32_e64 $src, (i32 (IMMAsI32 $rshift)), (i32 (IMMPopCount $mask)))
----------------
arsenm wrote:

This seems more like it should be a countTrailingOnes or countLeadingZeros than a popcount 

https://github.com/llvm/llvm-project/pull/182446