[InferAddressSpaces] collect flat address expression from return value (#70610)

If function return value's type is pointer, we can try to collect flat
address expression from it.
This PR also fixes noop_ptrint_pair_ce2 in noop-ptrint-pair.ll in #70611

Author: wenju-he

llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp

@@ -523,6 +523,10 @@ InferAddressSpacesImpl::collectFlatAddressExpressions(Function &F) const {
     } else if (auto *I2P = dyn_cast<IntToPtrInst>(&I)) {
       if (isNoopPtrIntCastPair(cast<Operator>(I2P), *DL, TTI))
         PushPtrOperand(cast<Operator>(I2P->getOperand(0))->getOperand(0));
+    } else if (auto *RI = dyn_cast<ReturnInst>(&I)) {
+      if (auto *RV = RI->getReturnValue();
+          RV && RV->getType()->isPtrOrPtrVectorTy())
+        PushPtrOperand(RV);
     }
   }
 

llvm/test/Transforms/InferAddressSpaces/AMDGPU/noop-ptrint-pair.ll

@@ -69,6 +69,13 @@ define ptr @noop_ptrint_pair_ce2() {
   ret ptr inttoptr (i64 ptrtoint (ptr addrspace(1) @g to i64) to ptr)
 }
 
+; COMMON-LABEL: @noop_ptrint_pair_ce2_vec(
+; AMDGCN-NEXT: ret <2 x ptr> <ptr addrspacecast (ptr addrspace(1) @g to ptr), ptr inttoptr (i64 ptrtoint (ptr addrspace(3) @l to i64) to ptr)>
+; NOTTI-NEXT: ret <2 x ptr> <ptr inttoptr (i64 ptrtoint (ptr addrspace(1) @g to i64) to ptr), ptr inttoptr (i64 ptrtoint (ptr addrspace(3) @l to i64) to ptr)>
+define <2 x ptr> @noop_ptrint_pair_ce2_vec() {
+  ret <2 x ptr> <ptr inttoptr (i64 ptrtoint (ptr addrspace(1) @g to i64) to ptr), ptr inttoptr (i64 ptrtoint (ptr addrspace(3) @l to i64) to ptr)>
+}
+
 ; COMMON-LABEL: @noop_ptrint_pair_ce3(
 ; AMDGCN-NEXT: %i = inttoptr i64 ptrtoint (ptr addrspace(1) @g to i64) to ptr
 ; AMDGCN-NEXT: ret void

llvm/test/Transforms/InferAddressSpaces/AMDGPU/select.ll

@@ -3,11 +3,11 @@
 ; Instcombine pulls the addrspacecast out of the select, make sure
 ;  this doesn't do something insane on non-canonical IR.
 
-; CHECK-LABEL: @return_select_group_flat(
-; CHECK-NEXT: %cast0 = addrspacecast ptr addrspace(3) %group.ptr.0 to ptr
-; CHECK-NEXT: %cast1 = addrspacecast ptr addrspace(3) %group.ptr.1 to ptr
-; CHECK-NEXT: %select = select i1 %c, ptr %cast0, ptr %cast1
-; CHECK-NEXT: ret ptr %select
+; CHECK-LABEL: define ptr @return_select_group_flat(
+; CHECK-SAME: i1 [[C:%.*]], ptr addrspace(3) [[GROUP_PTR_0:%.*]], ptr addrspace(3) [[GROUP_PTR_1:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[C]], ptr addrspace(3) [[GROUP_PTR_0]], ptr addrspace(3) [[GROUP_PTR_1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = addrspacecast ptr addrspace(3) [[SELECT]] to ptr
+; CHECK-NEXT:    ret ptr [[TMP1]]
 define ptr @return_select_group_flat(i1 %c, ptr addrspace(3) %group.ptr.0, ptr addrspace(3) %group.ptr.1) #0 {
   %cast0 = addrspacecast ptr addrspace(3) %group.ptr.0 to ptr
   %cast1 = addrspacecast ptr addrspace(3) %group.ptr.1 to ptr