[HLSL] Lower Length to SPIR-V backend (#102243)

This PR finishes #99134 by lowering the length function to the SPIR-V
backend. A test was added to verify that the generated SPIR-V is
correct.
Fixes #99134

Author: bob80905

llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp

@@ -175,6 +175,9 @@ class SPIRVInstructionSelector : public InstructionSelector {
   bool selectFmix(Register ResVReg, const SPIRVType *ResType,
                   MachineInstr &I) const;
 
+  bool selectLength(Register ResVReg, const SPIRVType *ResType,
+                    MachineInstr &I) const;
+
   bool selectFrac(Register ResVReg, const SPIRVType *ResType,
                   MachineInstr &I) const;
 
@@ -1372,6 +1375,23 @@ bool SPIRVInstructionSelector::selectFmix(Register ResVReg,
       .constrainAllUses(TII, TRI, RBI);
 }
 
+bool SPIRVInstructionSelector::selectLength(Register ResVReg,
+                                            const SPIRVType *ResType,
+                                            MachineInstr &I) const {
+
+  assert(I.getNumOperands() == 3);
+  assert(I.getOperand(2).isReg());
+  MachineBasicBlock &BB = *I.getParent();
+
+  return BuildMI(BB, I, I.getDebugLoc(), TII.get(SPIRV::OpExtInst))
+      .addDef(ResVReg)
+      .addUse(GR.getSPIRVTypeID(ResType))
+      .addImm(static_cast<uint32_t>(SPIRV::InstructionSet::GLSL_std_450))
+      .addImm(GL::Length)
+      .addUse(I.getOperand(2).getReg())
+      .constrainAllUses(TII, TRI, RBI);
+}
+
 bool SPIRVInstructionSelector::selectFrac(Register ResVReg,
                                            const SPIRVType *ResType,
                                            MachineInstr &I) const {
@@ -2118,6 +2138,8 @@ bool SPIRVInstructionSelector::selectIntrinsic(Register ResVReg,
     return selectAny(ResVReg, ResType, I);
   case Intrinsic::spv_lerp:
     return selectFmix(ResVReg, ResType, I);
+  case Intrinsic::spv_length:
+    return selectLength(ResVReg, ResType, I);
   case Intrinsic::spv_frac:
     return selectFrac(ResVReg, ResType, I);
   case Intrinsic::spv_rsqrt:

llvm/test/CodeGen/SPIRV/hlsl-intrinsics/length.ll

@@ -0,0 +1,29 @@
+; RUN: llc -O0 -mtriple=spirv-unknown-unknown %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv-unknown-unknown %s -o - -filetype=obj | spirv-val %}
+
+; Make sure SPIRV operation function calls for length are lowered correctly.
+
+; CHECK-DAG: %[[#op_ext_glsl:]] = OpExtInstImport "GLSL.std.450"
+; CHECK-DAG: %[[#float_32:]] = OpTypeFloat 32
+; CHECK-DAG: %[[#float_16:]] = OpTypeFloat 16
+; CHECK-DAG: %[[#vec4_float_16:]] = OpTypeVector %[[#float_16]] 4
+; CHECK-DAG: %[[#vec4_float_32:]] = OpTypeVector %[[#float_32]] 4
+
+define noundef half @length_half4(<4 x half> noundef %a) {
+entry:
+  ; CHECK: %[[#arg0:]] = OpFunctionParameter %[[#]]
+  ; CHECK: %[[#]] = OpExtInst %[[#float_16]] %[[#op_ext_glsl]] Length %[[#arg0]]
+  %hlsl.length = call half @llvm.spv.length.v4f16(<4 x half> %a)
+  ret half %hlsl.length
+}
+
+define noundef float @length_float4(<4 x float> noundef %a) {
+entry:
+  ; CHECK: %[[#arg0:]] = OpFunctionParameter %[[#]]
+  ; CHECK: %[[#]] = OpExtInst %[[#float_32]] %[[#op_ext_glsl]] Length %[[#arg0]]
+  %hlsl.length = call float @llvm.spv.length.v4f32(<4 x float> %a)
+  ret float %hlsl.length
+}
+
+declare half @llvm.spv.length.v4f16(<4 x half>)
+declare float @llvm.spv.length.v4f32(<4 x float>)