Add the 'initializes' attribute langref and support (#84803)

We propose adding a new LLVM attribute,
`initializes((Lo1,Hi1),(Lo2,Hi2),...)`, which expresses the notion of
memory space (i.e., intervals, in bytes) that the argument pointing to
is initialized in the function.

Will commit the attribute inferring in the follow-up PRs.


https://discourse.llvm.org/t/rfc-llvm-new-initialized-parameter-attribute-for-improved-interprocedural-dse/77337

1 files changed, 19 insertions, 6 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index b08d5c5..ba16c08 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -33,6 +33,7 @@
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/IR/Constant.h"
+#include "llvm/IR/ConstantRangeList.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
@@ -870,6 +871,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_DEAD_ON_UNWIND;
   case Attribute::Range:
     return bitc::ATTR_KIND_RANGE;
+  case Attribute::Initializes:
+    return bitc::ATTR_KIND_INITIALIZES;
   case Attribute::EndAttrKinds:
     llvm_unreachable("Can not encode end-attribute kinds marker.");
   case Attribute::None:
@@ -901,9 +904,10 @@ static void emitWideAPInt(SmallVectorImpl<uint64_t> &Vals, const APInt &A) {
 }
 
 static void emitConstantRange(SmallVectorImpl<uint64_t> &Record,
-                              const ConstantRange &CR) {
+                              const ConstantRange &CR, bool EmitBitWidth) {
   unsigned BitWidth = CR.getBitWidth();
-  Record.push_back(BitWidth);
+  if (EmitBitWidth)
+    Record.push_back(BitWidth);
   if (BitWidth > 64) {
     Record.push_back(CR.getLower().getActiveWords() |
                      (uint64_t(CR.getUpper().getActiveWords()) << 32));
@@ -954,11 +958,20 @@ void ModuleBitcodeWriter::writeAttributeGroupTable() {
         Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
         if (Ty)
           Record.push_back(VE.getTypeID(Attr.getValueAsType()));
-      } else {
-        assert(Attr.isConstantRangeAttribute());
+      } else if (Attr.isConstantRangeAttribute()) {
         Record.push_back(7);
         Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
-        emitConstantRange(Record, Attr.getValueAsConstantRange());
+        emitConstantRange(Record, Attr.getValueAsConstantRange(),
+                          /*EmitBitWidth=*/true);
+      } else {
+        assert(Attr.isConstantRangeListAttribute());
+        Record.push_back(8);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+        ArrayRef<ConstantRange> Val = Attr.getValueAsConstantRangeList();
+        Record.push_back(Val.size());
+        Record.push_back(Val[0].getBitWidth());
+        for (auto &CR : Val)
+          emitConstantRange(Record, CR, /*EmitBitWidth=*/false);
       }
     }
 
@@ -2788,7 +2801,7 @@ void ModuleBitcodeWriter::writeConstants(unsigned FirstVal, unsigned LastVal,
         Record.push_back(getOptimizationFlags(GO));
         if (std::optional<ConstantRange> Range = GO->getInRange()) {
           Code = bitc::CST_CODE_CE_GEP_WITH_INRANGE;
-          emitConstantRange(Record, *Range);
+          emitConstantRange(Record, *Range, /*EmitBitWidth=*/true);
         }
         for (unsigned i = 0, e = CE->getNumOperands(); i != e; ++i) {
           Record.push_back(VE.getTypeID(C->getOperand(i)->getType()));