[PATCH] Roundtrip the inalloca bit on allocas through bitcode

[Reid Kleckner]

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.  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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