[InstCombine] Preserve inalloca tag when transforming alloca

This is not meaningful in any practical sense, and just makes sure
we don't cause verifier failures.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -213,6 +213,7 @@ static Instruction *simplifyAllocaArraySize(InstCombinerImpl &IC,
       AllocaInst *New = IC.Builder.CreateAlloca(NewTy, AI.getAddressSpace(),
                                                 nullptr, AI.getName());
       New->setAlignment(AI.getAlign());
+      New->setUsedWithInAlloca(AI.isUsedWithInAlloca());
 
       replaceAllDbgUsesWith(AI, *New, *New, DT);
       return IC.replaceInstUsesWith(AI, New);

llvm/test/Transforms/InstCombine/alloca.ll

@@ -248,3 +248,14 @@ entry:
   call void (...) @use(ptr nonnull @int) [ "blah"(ptr %y) ]
   ret void
 }
+
+define void @test_inalloca_with_element_count(ptr %a) {
+; ALL-LABEL: @test_inalloca_with_element_count(
+; ALL-NEXT:    [[ALLOCA1:%.*]] = alloca inalloca [10 x %struct_type], align 4
+; ALL-NEXT:    call void @test9_aux(ptr nonnull inalloca([[STRUCT_TYPE:%.*]]) [[ALLOCA1]])
+; ALL-NEXT:    ret void
+;
+  %alloca = alloca inalloca %struct_type, i32 10, align 4
+  call void @test9_aux(ptr inalloca(%struct_type) %alloca)
+  ret void
+}