[clang] [llvm] [HLSL] Implement elementwise popcount (PR #108121)

[Farzon Lotfi via cfe-commits]

================
@@ -0,0 +1,28 @@
+; RUN: opt -S -dxil-op-lower -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+; Make sure dxil operation function calls for countbits are generated for all integer types.
+
+define noundef i16 @test_countbits_short(i16 noundef %a) {
+entry:
+; CHECK: call i16 @dx.op.unary.i16(i32 31, i16 %{{.*}})
+  %elt.ctpop = call i16 @llvm.ctpop.i16(i16 %a)
+  ret i16 %elt.ctpop
+}
+
+define noundef i32 @test_countbits_int(i32 noundef %a) {
+entry:
+; CHECK: call i32 @dx.op.unary.i32(i32 31, i32 %{{.*}})
+  %elt.ctpop = call i32 @llvm.ctpop.i32(i32 %a)
+  ret i32 %elt.ctpop
+}
+
+define noundef i64 @test_countbits_long(i64 noundef %a) {
+entry:
+; CHECK: call i64 @dx.op.unary.i64(i32 31, i64 %{{.*}})
+  %elt.ctpop = call i64 @llvm.ctpop.i64(i64 %a)
+  ret i64 %elt.ctpop
+}
+
----------------
farzonl wrote:

```suggestion
define noundef <4 x i32> @countbits_vec4_i32(<4 x i32> noundef %a) #0 {
entry:
  ; CHECK: [[ee0:%.*]] = extractelement <4 x i32> %a, i64 0
  ; CHECK: [[ie0:%.*]] = call i32 @dx.op.unary.i32(i32 31, i32 [[ee0]])
  ; CHECK: [[ee1:%.*]] = extractelement <4 x i32> %a, i64 1
  ; CHECK: [[ie1:%.*]] = call i32 @dx.op.unary.i32(i32 31, i32 [[ee1]])
  ; CHECK: [[ee2:%.*]] = extractelement <4 x i32> %a, i64 2
  ; CHECK: [[ie2:%.*]] = call i32 @dx.op.unary.i32(i32 31, i32 [[ee2]])
  ; CHECK: [[ee3:%.*]] = extractelement <4 x i32> %a, i64 3
  ; CHECK: [[ie3:%.*]] = call i32 @dx.op.unary.i32(i32 31, i32 [[ee3]])
  ; CHECK: insertelement <4 x i32> poison, i32 [[ie0]], i64 0
  ; CHECK: insertelement <4 x i32> %{{.*}}, i32 [[ie1]], i64 1
  ; CHECK: insertelement <4 x i32> %{{.*}}, i32 [[ie2]], i64 2
  ; CHECK: insertelement <4 x i32> %{{.*}}, i32 [[ie3]], i64 3
  %2 = call <4 x i32> @llvm.ctpop.v4i32(<4 x i32> %a) 
  ret <4 x i32> %2
}
```

https://github.com/llvm/llvm-project/pull/108121