[AMDGPU] Trim trailing undefs from the end of image and buffer store

Remove undef values from the end of the vector operand in image and
buffer store instructions.
Also instead of call to computeKnownFPClass, use only findScalarElement.

Continuation of: 88421ea Trim zero components from buffer and image stores

Differential Revision: https://reviews.llvm.org/D152440

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

@@ -385,17 +385,20 @@ static APInt trimTrailingZerosInVector(InstCombiner &IC, Value *UseV,
   APInt DemandedElts = APInt::getAllOnes(VWidth);
 
   for (int i = VWidth - 1; i > 0; --i) {
-    APInt DemandOneElt = APInt::getOneBitSet(VWidth, i);
-    KnownFPClass KnownFPClass =
-        computeKnownFPClass(UseV, DemandOneElt, IC.getDataLayout(),
-                            /*InterestedClasses=*/fcAllFlags,
-                            /*Depth=*/0, &IC.getTargetLibraryInfo(),
-                            &IC.getAssumptionCache(), I,
-                            &IC.getDominatorTree());
-    if (KnownFPClass.KnownFPClasses != fcPosZero)
+    auto *Elt = findScalarElement(UseV, i);
+    if (!Elt)
       break;
+
+    if (auto *ConstElt = dyn_cast<Constant>(Elt)) {
+      if (!ConstElt->isNullValue() && !isa<UndefValue>(Elt))
+        break;
+    } else {
+      break;
+    }
+
     DemandedElts.clearBit(i);
   }
+
   return DemandedElts;
 }
 

llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-simplify-image-buffer-stores.ll

@@ -84,6 +84,19 @@ define amdgpu_ps void @struct_tbuffer_store_insert_zeros_at_beginning(<4 x i32>
   ret void
 }
 
+define amdgpu_ps void @struct_tbuffer_store_insert_undefs(<4 x i32> inreg %a, float %vdata1, i32 %b) {
+; GCN-LABEL: @struct_tbuffer_store_insert_undefs(
+; GCN-NEXT:    [[TMP1:%.*]] = insertelement <2 x float> <float poison, float 1.000000e+00>, float [[VDATA1:%.*]], i64 0
+; GCN-NEXT:    call void @llvm.amdgcn.struct.tbuffer.store.v2f32(<2 x float> [[TMP1]], <4 x i32> [[A:%.*]], i32 [[B:%.*]], i32 0, i32 42, i32 0, i32 15)
+; GCN-NEXT:    ret void
+;
+  %newvdata1 = insertelement <4 x float> poison, float %vdata1, i32 0
+  %newvdata2 = insertelement <4 x float> %newvdata1, float 1.0, i32 1
+  call void @llvm.amdgcn.struct.tbuffer.store.v4f32(<4 x float> %newvdata2, <4 x i32> %a, i32 %b, i32 0, i32 42, i32 0, i32 15)
+  ret void
+}
+
+
 declare void @llvm.amdgcn.raw.buffer.store.format.v4f32(<4 x float>, <4 x i32>, i32, i32, i32) #2
 declare void @llvm.amdgcn.buffer.store.format.v4f32(<4 x float>, <4 x i32>, i32, i32, i1, i1) #1
 declare void @llvm.amdgcn.struct.buffer.store.format.v4f32(<4 x float>, <4 x i32>, i32, i32, i32, i32) #2