Discard @llvm.invariant.group.barrier in -O0 code generation

[rsmith]

Summary

Fix isel failure from -O0 by discarding @llvm.invariant.group.barrier intrinsics.

[hfinkel]

LGTM

We should probably also add this to isAssumeLikeIntrinsic in Analysis/ValueTracking.cpp and getIntrinsicCost in include/llvm/Analysis/TargetTransformInfoImpl.h.

lib/CodeGen/SelectionDAG/FastISel.cpp

   case Intrinsic::objectsize: {
     ConstantInt *CI = cast<ConstantInt>(II->getArgOperand(1));
     unsigned long long Res = CI->isZero() ? -1ULL : 0;
     Constant *ResCI = ConstantInt::get(II->getType(), Res);
     unsigned ResultReg = getRegForValue(ResCI);
     if (!ResultReg)
       return false;
     updateValueMap(II, ResultReg);
     return true;
   }
+  case Intrinsic::invariant_group_barrier:
   case Intrinsic::expect: {
     unsigned ResultReg = getRegForValue(II->getArgOperand(0));
     if (!ResultReg)
       return false;
     updateValueMap(II, ResultReg);
     return true;
   }
   case Intrinsic::experimental_stackmap:
     return selectStackmap(II);
   case Intrinsic::experimental_patchpoint_void:

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

     if (CI->isZero())
       Res = DAG.getConstant(-1ULL, sdl, Ty);
     else
       Res = DAG.getConstant(0, sdl, Ty);
 
     setValue(&I, Res);
     return nullptr;
   }
   case Intrinsic::annotation:
   case Intrinsic::ptr_annotation:
+  case Intrinsic::invariant_group_barrier:
     // Drop the intrinsic, but forward the value
     setValue(&I, getValue(I.getOperand(0)));
     return nullptr;
   case Intrinsic::assume:
   case Intrinsic::var_annotation:
     // Discard annotate attributes and assumptions
     return nullptr;
 
   case Intrinsic::init_trampoline: {
     const Function *F = cast<Function>(I.getArgOperand(1)->stripPointerCasts());

test/CodeGen/Generic/intrinsics.ll

 ; RUN: llc < %s
+; RUN: llc -O0 < %s
 
 ;; SQRT
 declare float @llvm.sqrt.f32(float)
 
 declare double @llvm.sqrt.f64(double)
 
 define double @test_sqrt(float %F) {
         %G = call float @llvm.sqrt.f32( float %F )              ; <float> [#uses=1]
         %H = fpext float %G to double           ; <double> [#uses=1]
         %I = call double @llvm.sqrt.f64( double %H )            ; <double> [#uses=1]

 
 declare double @cos(double) readonly
 
 define double @test_cos(float %F) {
         %G = call float @cosf( float %F )               ; <float> [#uses=1]
         %H = fpext float %G to double           ; <double> [#uses=1]
         %I = call double @cos( double %H )              ; <double> [#uses=1]
         ret double %I
 }
 
+declare i8* @llvm.invariant.group.barrier(i8*)
+
+define i8* @barrier(i8* %p) {
+        %q = call i8* @llvm.invariant.group.barrier(i8* %p)
+        ret i8* %q
+}