[LLVMdev] Documentation of bitcasts in calls (original) (raw)

Jeremy Lakeman Jeremy.Lakeman at gmail.com
Mon Jul 13 05:15:31 PDT 2015

Textual LLVM IR is not guaranteed to be stable between versions. Even LLVM's parser is not guaranteed to be backwards compatible.

There was/is a move afoot to remove types from pointers, so explicit bitcasts are no longer required or used. Instead each instruction that uses a pointer will also take a type parameter for that pointer.

Casts that don't change the value, don't result in machine instructions anyway.

On Mon, Jul 13, 2015 at 9:16 PM, Thomas Ströder < stroeder at informatik.rwth-aachen.de> wrote:

Dear all,

I just stumbled over the following instruction in the LLVM IR of a C program compiled with clang: %26 = call i32 (...)* bitcast (i32 (i32, i32, i32, i32, i32)* @KeWaitForSingleObject to i32 (...)*)(i32 %23, i32 %24, i32 %25, i32 0, i32 0) Since our LLVM Parser choked on this instruction, I tried to check the documentation, but did not find anything about such nested bitcasts within calls. What is the exact syntax and semantics (while I can guess the latter, especially the former is interesting for me when building a parser for LLVM IR) for such instructions and/or where is this documented? In particular, the parantheses around the arguments of the bitcast are confusing me. Alternatively, is there a way to tell clang not to inline such bitcasts, but have them in a separate instruction before and use the result in the call? Best regards, Thomas

-- Thomas Ströder mailto:stroeder at informatik.rwth-aachen.de LuFG Informatik 2 http://verify.rwth-aachen.de/stroeder RWTH Aachen phone: +49 241 80-21241

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