X86: Don't make illegal GOTTPOFF relocations

"ELF Handling for Thread-Local Storage" specifies that R_X86_64_GOTTPOFF
relocation target a movq or addq instruction.

Prohibit the truncation of such loads to movl or addl.

This fixes PR22083.

Differential Revision: http://reviews.llvm.org/D6839

llvm-svn: 225250

2 files changed, 17 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 9e068616ddc..98935890d36 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3862,6 +3862,18 @@ bool X86TargetLowering::isFPImmLegal(const APFloat &Imm, EVT VT) const {
   return false;
 }
 
+bool X86TargetLowering::shouldReduceLoadWidth(SDNode *Load,
+                                              ISD::LoadExtType ExtTy,
+                                              EVT NewVT) const {
+  // "ELF Handling for Thread-Local Storage" specifies that R_X86_64_GOTTPOFF
+  // relocation target a movq or addq instruction: don't let the load shrink.
+  SDValue BasePtr = cast<LoadSDNode>(Load)->getBasePtr();
+  if (BasePtr.getOpcode() == X86ISD::WrapperRIP)
+    if (const auto *GA = dyn_cast<GlobalAddressSDNode>(BasePtr.getOperand(0)))
+      return GA->getTargetFlags() != X86II::MO_GOTTPOFF;
+  return true;
+}
+
 /// \brief Returns true if it is beneficial to convert a load of a constant
 /// to just the constant itself.
 bool X86TargetLowering::shouldConvertConstantLoadToIntImm(const APInt &Imm,
diff --git a/llvm/lib/Target/X86/X86ISelLowering.h b/llvm/lib/Target/X86/X86ISelLowering.h
index 0b01bae9e67..ba077a8a0b4 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.h
+++ b/llvm/lib/Target/X86/X86ISelLowering.h
@@ -770,6 +770,11 @@ namespace llvm {
       return !X86ScalarSSEf64 || VT == MVT::f80;
     }
 
+    /// Return true if we believe it is correct and profitable to reduce the
+    /// load node to a smaller type.
+    bool shouldReduceLoadWidth(SDNode *Load, ISD::LoadExtType ExtTy,
+                               EVT NewVT) const override;
+
     const X86Subtarget* getSubtarget() const {
       return Subtarget;
     }