[PATCH] Roundtrip the inalloca bit on allocas through bitcode

[Nick Lewycky]

Reid Kleckner wrote:
> Hi nicholas, nlewycky,
>
> This was an oversight in the original support.  As it is, I stuffed this
> bit into the alignment.  The alignment is stored in log2 form, so it
> doesn't need more than 6 bits.

How was alloca encoded in the 3.4 release? What would it someone need to 
have in their 3.4 .bc file to cause it to be read as inalloca in 3.5? 
"align 18446744073709551616"?

   On the other hand, adding a separate
> record might be cleaner.  Hence, I'm asking for a review, since we can't
> change the decision once we make it.
>
> http://reviews.llvm.org/D3943
>
> Files:
>    include/llvm/Bitcode/LLVMBitCodes.h
>    lib/Bitcode/Reader/BitcodeReader.cpp
>    lib/Bitcode/Writer/BitcodeWriter.cpp
>    test/Bitcode/inalloca.ll
>
> Index: include/llvm/Bitcode/LLVMBitCodes.h
> ===================================================================
> --- include/llvm/Bitcode/LLVMBitCodes.h
> +++ include/llvm/Bitcode/LLVMBitCodes.h
> @@ -289,7 +289,7 @@
>       FUNC_CODE_INST_PHI         = 16, // PHI:        [ty, val0,bb0, ...]
>       // 17 is unused.
>       // 18 is unused.
> -    FUNC_CODE_INST_ALLOCA      = 19, // ALLOCA:     [instty, op, align]
> +    FUNC_CODE_INST_ALLOCA      = 19, // ALLOCA:     [instty, opty, op, align]
>       FUNC_CODE_INST_LOAD        = 20, // LOAD:       [opty, op, align, vol]
>       // 21 is unused.
>       // 22 is unused.
> Index: lib/Bitcode/Reader/BitcodeReader.cpp
> ===================================================================
> --- lib/Bitcode/Reader/BitcodeReader.cpp
> +++ lib/Bitcode/Reader/BitcodeReader.cpp
> @@ -2874,10 +2874,14 @@
>           dyn_cast_or_null<PointerType>(getTypeByID(Record[0]));
>         Type *OpTy = getTypeByID(Record[1]);
>         Value *Size = getFnValueByID(Record[2], OpTy);
> -      unsigned Align = Record[3];
> +      unsigned AlignBits = Record[3];
> +      bool InAlloca = AlignBits&  (1<<  6);
> +      unsigned Align = AlignBits&  ((1<<  6) - 1);
>         if (!Ty || !Size)
>           return Error(InvalidRecord);
> -      I = new AllocaInst(Ty->getElementType(), Size, (1<<  Align)>>  1);
> +      AllocaInst *AI = new AllocaInst(Ty->getElementType(), Size, (1<<  Align)>>  1);
> +      AI->setUsedWithInAlloca(InAlloca);
> +      I = AI;
>         InstructionList.push_back(I);
>         break;
>       }
> Index: lib/Bitcode/Writer/BitcodeWriter.cpp
> ===================================================================
> --- lib/Bitcode/Writer/BitcodeWriter.cpp
> +++ lib/Bitcode/Writer/BitcodeWriter.cpp
> @@ -1397,13 +1397,18 @@
>       break;
>     }
>
> -  case Instruction::Alloca:
> +  case Instruction::Alloca: {
>       Code = bitc::FUNC_CODE_INST_ALLOCA;
>       Vals.push_back(VE.getTypeID(I.getType()));
>       Vals.push_back(VE.getTypeID(I.getOperand(0)->getType()));
>       Vals.push_back(VE.getValueID(I.getOperand(0))); // size.
> -    Vals.push_back(Log2_32(cast<AllocaInst>(I).getAlignment())+1);
> +    const AllocaInst&AI = cast<AllocaInst>(I);
> +    unsigned AlignRecord = Log2_32(AI.getAlignment()) + 1;
> +    assert(AlignRecord<  1<<  6&&  "alignment greater than 1<<  64");
> +    AlignRecord |= AI.isUsedWithInAlloca()<<  6;
> +    Vals.push_back(AlignRecord);
>       break;
> +  }
>
>     case Instruction::Load:
>       if (cast<LoadInst>(I).isAtomic()) {
> Index: test/Bitcode/inalloca.ll
> ===================================================================
> --- /dev/null
> +++ test/Bitcode/inalloca.ll
> @@ -0,0 +1,17 @@
> +; RUN: llvm-as<  %s | llvm-dis | FileCheck %s
> +
> +; inalloca should roundtrip.
> +
> +define void @foo(i32* inalloca %args) {
> +  ret void
> +}
> +; CHECK-LABEL: define void @foo(i32* inalloca %args)
> +
> +define void @bar() {
> +  %args = alloca inalloca i32
> +  call void @foo(i32* inalloca %args)
> +  ret void
> +}
> +; CHECK-LABEL: define void @bar() {
> +; CHECK: %args = alloca inalloca i32
> +; CHECK: call void @foo(i32* inalloca %args)
>
>
>
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