[DirectX] Remove llvm.assume intrinsic

fixes llvm#165051

This change reverts the experiment we did for llvm#165311

While some backends seem to support llvm.assume without validation
The validator itself does not so it makes more sense to just remove it.

Author: farzonl

llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp

@@ -197,6 +197,7 @@ static Value *expand16BitIsNormal(CallInst *Orig) {
 
 static bool isIntrinsicExpansion(Function &F) {
   switch (F.getIntrinsicID()) {
+  case Intrinsic::assume:
   case Intrinsic::abs:
   case Intrinsic::atan2:
   case Intrinsic::exp:
@@ -988,6 +989,9 @@ static bool expandIntrinsic(Function &F, CallInst *Orig) {
   case Intrinsic::abs:
     Result = expandAbs(Orig);
     break;
+  case Intrinsic::assume:
+    Orig->eraseFromParent();
+    return true;
   case Intrinsic::atan2:
     Result = expandAtan2Intrinsic(Orig);
     break;

llvm/lib/Target/DirectX/DXILOpLowering.cpp

@@ -904,8 +904,6 @@ class OpLowerer {
       case Intrinsic::dx_resource_casthandle:
       // NOTE: llvm.dbg.value is supported as is in DXIL.
       case Intrinsic::dbg_value:
-      // NOTE: llvm.assume is supported as is in DXIL.
-      case Intrinsic::assume:
       case Intrinsic::not_intrinsic:
         if (F.use_empty())
           F.eraseFromParent();

llvm/test/CodeGen/DirectX/llvm_assume.ll

@@ -0,0 +1,9 @@
+; RUN: opt -S -dxil-intrinsic-expansion -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+define void @test_llvm_assume(i1 %0)  {
+; CHECK-LABEL: test_llvm_assume
+; CHECK-NEXT: ret void
+tail call void @llvm.assume(i1 %0)
+ret void
+}
+