[LLVMdev] What is the front end pattern?

[gamma_chen]

I find this pattern as below from <llvm-source-tree>/test/CodeGen/Mips/alloca.ll.
Do you know what front end pattern can be translated into this pattern alloca with variable argument %size as below? 
Can some one help me? I am writing the llvm backend document --http://jonathan2251.github.com/lbd/index.html now.

%tmp1 = alloca i8, i32 %size, align 4 // has %size variable, not pattern, alloca i8, align 4

define i32 @twoalloca(i32 %size) nounwind {
entry:
...
? %tmp1 = alloca i8, i32 %size, align 4
}

Jonathan
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