[DirectX] Allow llvm lifetime intrinsics to pass on to the DirectX backend (llvm#136622)

fixes llvm#136620

It was determined that the lifetime intrinsics generated by clang are
likely more correct than the ones in DXC hence explaining the missing
lifetimes between the IR diffs.

As such we are legalizing lllvm lifetime intrinsics by letting them all
pass on through.

Author: farzonl

llvm/lib/Target/DirectX/DXILOpLowering.cpp

@@ -753,6 +753,8 @@ class OpLowerer {
       case Intrinsic::dx_resource_casthandle:
       // NOTE: llvm.dbg.value is supported as is in DXIL.
       case Intrinsic::dbg_value:
+      case Intrinsic::lifetime_start:
+      case Intrinsic::lifetime_end:
       case Intrinsic::not_intrinsic:
         continue;
       default: {

llvm/test/CodeGen/DirectX/legalize-lifetimes.ll

@@ -0,0 +1,18 @@
+; RUN: opt -S -passes='dxil-op-lower' -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+; CHECK-LABEL: define void @test_legal_lifetime() {
+; CHECK-NEXT:    [[ACCUM_I_FLAT:%.*]] = alloca [1 x i32], align 4
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i32, ptr [[ACCUM_I_FLAT]], i32 0
+; CHECK-NEXT:    call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[ACCUM_I_FLAT]])
+; CHECK-NEXT:    store i32 0, ptr [[GEP]], align 4
+; CHECK-NEXT:    call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[ACCUM_I_FLAT]])
+; CHECK-NEXT:    ret void
+;
+define void @test_legal_lifetime()  {
+  %accum.i.flat = alloca [1 x i32], align 4
+  %gep = getelementptr i32, ptr %accum.i.flat, i32 0
+  call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %accum.i.flat)
+  store i32 0, ptr %gep, align 4
+  call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %accum.i.flat)
+  ret void
+}