[PATCH] D29284: [AMDGPU] Lower null pointers in static variable initializer

[Yaxun Liu via Phabricator via llvm-commits]

yaxunl created this revision.
Herald added subscribers: tpr, tony-tye, nhaehnle, wdng, kzhuravl.

For amdgcn target Clang generates addrspacecast to represent null pointers in private and local address spaces.

In LLVM codegen, the static variable initializer is lowered by virtual function AsmPrinter::lowerConstant which is target generic. Since addrspacecast is target specific,  AsmPrinter::lowerConstant is unable to lower addrspacecast in the null pointer representation.

This patch overrides AsmPrinter::lowerConstant with AMDGPUAsmPrinter::lowerConstant, which is able to lower the target-specific addrspacecast in the null pointer representation so that -1 is correctly emitted in codeobject as initial value for null pointers.


https://reviews.llvm.org/D29284

Files:
  lib/Target/AMDGPU/AMDGPUAsmPrinter.h
  lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
  test/CodeGen/AMDGPU/nullptr.ll


Index: test/CodeGen/AMDGPU/nullptr.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/nullptr.ll
@@ -0,0 +1,20 @@
+;RUN: llc < %s -march=amdgcn -verify-machineinstrs | FileCheck %s
+
+%struct.S = type { i32 addrspace(1)*, i32 addrspace(3)*, i32* }
+
+; CHECK-LABEL: nullptr_priv:
+; CHECK-NEXT: .long -1
+ at nullptr_priv = global i32* addrspacecast (i32 addrspace(4)* null to i32*)
+
+; CHECK-LABEL: nullptr_local:
+; CHECK-NEXT: .long -1
+ at nullptr_local = global i32 addrspace(3)* addrspacecast (i32 addrspace(4)* null to i32 addrspace(3)*)
+
+; CHECK-LABEL: structWithPointers:
+; CHECK-NEXT: .quad 0
+; CHECK-NEXT: .long -1
+; CHECK-NEXT: .long -1
+ at structWithPointers = addrspace(1) global %struct.S {
+  i32 addrspace(1)* null,
+  i32 addrspace(3)* addrspacecast (i32 addrspace(4)* null to i32 addrspace(3)*),
+  i32* addrspacecast (i32 addrspace(4)* null to i32*) }, align 4
Index: lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
===================================================================
--- lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
+++ lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
@@ -151,6 +151,27 @@
   return MCInstLowering.lowerOperand(MO, MCOp);
 }
 
+const MCExpr *AMDGPUAsmPrinter::lowerConstant(const Constant *CV) {
+  auto CE = dyn_cast<ConstantExpr>(CV);
+
+  // Lower null pointers in private and local address space.
+  // Clang generates addrspacecast for null pointers in private and local
+  // address space, which needs to be lowered.
+  if (CE && CE->getOpcode() == Instruction::AddrSpaceCast) {
+    auto Op = CE->getOperand(0);
+    if (Op->isNullValue()) {
+      auto SrcAddr = Op->getType()->getPointerAddressSpace();
+      auto DstAddr = CE->getType()->getPointerAddressSpace();
+      if (SrcAddr == AMDGPUAS::FLAT_ADDRESS &&
+          (DstAddr == AMDGPUAS::PRIVATE_ADDRESS ||
+           DstAddr == AMDGPUAS::LOCAL_ADDRESS)) {
+        return MCConstantExpr::create(-1, OutContext);
+      }
+    }
+  }
+  return AsmPrinter::lowerConstant(CV);
+}
+
 void AMDGPUAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   if (emitPseudoExpansionLowering(*OutStreamer, MI))
     return;
Index: lib/Target/AMDGPU/AMDGPUAsmPrinter.h
===================================================================
--- lib/Target/AMDGPU/AMDGPUAsmPrinter.h
+++ lib/Target/AMDGPU/AMDGPUAsmPrinter.h
@@ -111,6 +111,11 @@
   /// pseudo lowering.
   bool lowerOperand(const MachineOperand &MO, MCOperand &MCOp) const;
 
+  /// \brief Lower the specified LLVM Constant to an MCExpr.
+  /// The AsmPrinter::lowerConstantof does not know how to lower
+  /// addrspacecast, therefore they should be lowered by this function.
+  const MCExpr *lowerConstant(const Constant *CV) override;
+
   /// \brief tblgen'erated driver function for lowering simple MI->MC pseudo
   /// instructions.
   bool emitPseudoExpansionLowering(MCStreamer &OutStreamer,


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D29284.86290.patch
Type: text/x-patch
Size: 2907 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170130/72ae8d07/attachment-0001.bin>