[MS][ARM64] Hoist __ImageBase handling into TargetLoweringObjectFileCOFF

All COFF targets should use @IMGREL32 relocations for symbol differences
against __ImageBase. Do the same for getSectionForConstant, so that
immediates lowered to globals get merged across TUs.

Patch by Chris January

Differential Revision: https://reviews.llvm.org/D47783

llvm-svn: 334523

1 files changed, 105 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 85ad78e..0b8d522 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1274,6 +1274,111 @@ void TargetLoweringObjectFileCOFF::emitLinkerFlagsForUsed(
   emitLinkerFlagsForUsedCOFF(OS, GV, getTargetTriple(), getMangler());
 }
 
+const MCExpr *TargetLoweringObjectFileCOFF::lowerRelativeReference(
+    const GlobalValue *LHS, const GlobalValue *RHS,
+    const TargetMachine &TM) const {
+  const Triple &T = TM.getTargetTriple();
+  if (!T.isKnownWindowsMSVCEnvironment() &&
+      !T.isWindowsItaniumEnvironment() &&
+      !T.isWindowsCoreCLREnvironment())
+    return nullptr;
+
+  // Our symbols should exist in address space zero, cowardly no-op if
+  // otherwise.
+  if (LHS->getType()->getPointerAddressSpace() != 0 ||
+      RHS->getType()->getPointerAddressSpace() != 0)
+    return nullptr;
+
+  // Both ptrtoint instructions must wrap global objects:
+  // - Only global variables are eligible for image relative relocations.
+  // - The subtrahend refers to the special symbol __ImageBase, a GlobalVariable.
+  // We expect __ImageBase to be a global variable without a section, externally
+  // defined.
+  //
+  // It should look something like this: @__ImageBase = external constant i8
+  if (!isa<GlobalObject>(LHS) || !isa<GlobalVariable>(RHS) ||
+      LHS->isThreadLocal() || RHS->isThreadLocal() ||
+      RHS->getName() != "__ImageBase" || !RHS->hasExternalLinkage() ||
+      cast<GlobalVariable>(RHS)->hasInitializer() || RHS->hasSection())
+    return nullptr;
+
+  return MCSymbolRefExpr::create(TM.getSymbol(LHS),
+                                 MCSymbolRefExpr::VK_COFF_IMGREL32,
+                                 getContext());
+}
+
+static std::string APIntToHexString(const APInt &AI) {
+  unsigned Width = (AI.getBitWidth() / 8) * 2;
+  std::string HexString = utohexstr(AI.getLimitedValue(), /*LowerCase=*/true);
+  unsigned Size = HexString.size();
+  assert(Width >= Size && "hex string is too large!");
+  HexString.insert(HexString.begin(), Width - Size, '0');
+
+  return HexString;
+}
+
+static std::string scalarConstantToHexString(const Constant *C) {
+  Type *Ty = C->getType();
+  if (isa<UndefValue>(C)) {
+    return APIntToHexString(APInt::getNullValue(Ty->getPrimitiveSizeInBits()));
+  } else if (const auto *CFP = dyn_cast<ConstantFP>(C)) {
+    return APIntToHexString(CFP->getValueAPF().bitcastToAPInt());
+  } else if (const auto *CI = dyn_cast<ConstantInt>(C)) {
+    return APIntToHexString(CI->getValue());
+  } else {
+    unsigned NumElements;
+    if (isa<VectorType>(Ty))
+      NumElements = Ty->getVectorNumElements();
+    else
+      NumElements = Ty->getArrayNumElements();
+    std::string HexString;
+    for (int I = NumElements - 1, E = -1; I != E; --I)
+      HexString += scalarConstantToHexString(C->getAggregateElement(I));
+    return HexString;
+  }
+}
+
+MCSection *TargetLoweringObjectFileCOFF::getSectionForConstant(
+    const DataLayout &DL, SectionKind Kind, const Constant *C,
+    unsigned &Align) const {
+  if (Kind.isMergeableConst() && C) {
+    const unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
+                                     COFF::IMAGE_SCN_MEM_READ |
+                                     COFF::IMAGE_SCN_LNK_COMDAT;
+    std::string COMDATSymName;
+    if (Kind.isMergeableConst4()) {
+      if (Align <= 4) {
+        COMDATSymName = "__real@" + scalarConstantToHexString(C);
+        Align = 4;
+      }
+    } else if (Kind.isMergeableConst8()) {
+      if (Align <= 8) {
+        COMDATSymName = "__real@" + scalarConstantToHexString(C);
+        Align = 8;
+      }
+    } else if (Kind.isMergeableConst16()) {
+      // FIXME: These may not be appropriate for non-x86 architectures.
+      if (Align <= 16) {
+        COMDATSymName = "__xmm@" + scalarConstantToHexString(C);
+        Align = 16;
+      }
+    } else if (Kind.isMergeableConst32()) {
+      if (Align <= 32) {
+        COMDATSymName = "__ymm@" + scalarConstantToHexString(C);
+        Align = 32;
+      }
+    }
+
+    if (!COMDATSymName.empty())
+      return getContext().getCOFFSection(".rdata", Characteristics, Kind,
+                                         COMDATSymName,
+                                         COFF::IMAGE_COMDAT_SELECT_ANY);
+  }
+
+  return TargetLoweringObjectFile::getSectionForConstant(DL, Kind, C, Align);
+}
+
+
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 //                                  Wasm
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