Add alloca instruction to Subzero bitcode reader. BUG= https://code.google.com/p/nativeclient/issues/detail?id=3894 R=jvoung@chromium.org, stichnot@chromium.org Review URL: https://codereview.chromium.org/545623005

diff --git a/src/PNaClTranslator.cpp b/src/PNaClTranslator.cpp
index 5bfa33b..bde906a 100644
--- a/src/PNaClTranslator.cpp
+++ b/src/PNaClTranslator.cpp

@@ -845,6 +845,8 @@
   // True if the last processed instruction was a terminating
   // instruction.
   bool InstIsTerminating;
+  // Upper limit of alignment power allowed by LLVM
+  static const uint64_t AlignPowerLimit = 29;
 
   virtual bool ParseBlock(unsigned BlockID) LLVM_OVERRIDE;
 
@@ -1515,6 +1517,34 @@
     InstIsTerminating = true;
     break;
   }
+  case naclbitc::FUNC_CODE_INST_ALLOCA: {
+    // ALLOCA: [Size, align]
+    if (!isValidRecordSize(2, "function block alloca"))
+      return;
+    Ice::Operand *ByteCount = getRelativeOperand(Values[0]);
+    if (ByteCount->getType() != Ice::IceType_i32) {
+      std::string Buffer;
+      raw_string_ostream StrBuf(Buffer);
+      StrBuf << "Alloca on non-i32 value. Found: " << ByteCount;
+      Error(StrBuf.str());
+      return;
+    }
+    uint64_t AlignPower = Values[1];
+    unsigned Alignment = 1;
+    if (AlignPower <= AlignPowerLimit) {
+      Alignment = (1 << static_cast<unsigned>(AlignPower)) >> 1;
+    } else {
+      std::string Buffer;
+      raw_string_ostream StrBuf(Buffer);
+      StrBuf << "Alloca on alignment greater than 2**" << AlignPowerLimit
+             << ". Found: 2**" << AlignPower;
+      Error(StrBuf.str());
+      // TODO(kschimpf) Remove error recovery once implementation complete.
+    }
+    Ice::Variable *Dest = NextInstVar(Context->getIcePointerType());
+    Inst = Ice::InstAlloca::create(Func, ByteCount, Alignment, Dest);
+    break;
+  }
   default:
     // Generate error message!
     BlockParserBaseClass::ProcessRecord();