[arm] Fix Unnecessary reloads from GOT.

Summary:
This fixes PR35221.
Use pseudo-instructions to let MachineCSE hoist global address computation.

Subscribers: aemerson, javed.absar, kristof.beyls, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D39871

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318081 91177308-0d34-0410-b5e6-96231b3b80d8

12 files changed, 78 insertions, 43 deletions

diff --git a/lib/Target/ARM/ARMExpandPseudoInsts.cpp b/lib/Target/ARM/ARMExpandPseudoInsts.cpp
index be7afae5ea4..bf67bbdc379 100644
--- a/lib/Target/ARM/ARMExpandPseudoInsts.cpp
+++ b/lib/Target/ARM/ARMExpandPseudoInsts.cpp
@@ -1311,6 +1311,7 @@ bool ARMExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
       unsigned DstReg = MI.getOperand(0).getReg();
       bool DstIsDead = MI.getOperand(0).isDead();
       const MachineOperand &MO1 = MI.getOperand(1);
+      auto Flags = MO1.getTargetFlags();
       const GlobalValue *GV = MO1.getGlobal();
       bool IsARM =
           Opcode != ARM::tLDRLIT_ga_pcrel && Opcode != ARM::tLDRLIT_ga_abs;
@@ -1329,7 +1330,9 @@ bool ARMExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
 
       if (IsPIC) {
         unsigned PCAdj = IsARM ? 8 : 4;
-        auto Modifier = STI->getCPModifier(GV);
+        auto Modifier = (Flags & ARMII::MO_GOT)
+                            ? ARMCP::GOT_PREL
+                            : ARMCP::no_modifier;
         ARMPCLabelIndex = AFI->createPICLabelUId();
         CPV = ARMConstantPoolConstant::Create(
             GV, ARMPCLabelIndex, ARMCP::CPValue, PCAdj, Modifier,
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 135e20cf22f..44837898709 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -3164,28 +3164,12 @@ SDValue ARMTargetLowering::LowerGlobalAddressELF(SDValue Op,
 
   if (isPositionIndependent()) {
     bool UseGOT_PREL = !TM.shouldAssumeDSOLocal(*GV->getParent(), GV);
-
-    MachineFunction &MF = DAG.getMachineFunction();
-    ARMFunctionInfo *AFI = MF.getInfo<ARMFunctionInfo>();
-    unsigned ARMPCLabelIndex = AFI->createPICLabelUId();
-    EVT PtrVT = getPointerTy(DAG.getDataLayout());
-    SDLoc dl(Op);
-    unsigned PCAdj = Subtarget->isThumb() ? 4 : 8;
-    ARMConstantPoolValue *CPV = ARMConstantPoolConstant::Create(
-        GV, ARMPCLabelIndex, ARMCP::CPValue, PCAdj,
-        UseGOT_PREL ? ARMCP::GOT_PREL : ARMCP::no_modifier,
-        /*AddCurrentAddress=*/UseGOT_PREL);
-    SDValue CPAddr = DAG.getTargetConstantPool(CPV, PtrVT, 4);
-    CPAddr = DAG.getNode(ARMISD::Wrapper, dl, MVT::i32, CPAddr);
-    SDValue Result = DAG.getLoad(
-        PtrVT, dl, DAG.getEntryNode(), CPAddr,
-        MachinePointerInfo::getConstantPool(DAG.getMachineFunction()));
-    SDValue Chain = Result.getValue(1);
-    SDValue PICLabel = DAG.getConstant(ARMPCLabelIndex, dl, MVT::i32);
-    Result = DAG.getNode(ARMISD::PIC_ADD, dl, PtrVT, Result, PICLabel);
+    SDValue G = DAG.getTargetGlobalAddress(GV, dl, PtrVT, 0,
+                                           UseGOT_PREL ? ARMII::MO_GOT : 0);
+    SDValue Result = DAG.getNode(ARMISD::WrapperPIC, dl, PtrVT, G);
     if (UseGOT_PREL)
       Result =
-          DAG.getLoad(PtrVT, dl, Chain, Result,
+          DAG.getLoad(PtrVT, dl, DAG.getEntryNode(), Result,
                       MachinePointerInfo::getGOT(DAG.getMachineFunction()));
     return Result;
   } else if (Subtarget->isROPI() && IsRO) {
diff --git a/lib/Target/ARM/ARMInstrInfo.td b/lib/Target/ARM/ARMInstrInfo.td
index c031f6ff7ac..d8cd076c17a 100644
--- a/lib/Target/ARM/ARMInstrInfo.td
+++ b/lib/Target/ARM/ARMInstrInfo.td
@@ -332,6 +332,8 @@ def UseNegativeImmediates :
 let RecomputePerFunction = 1 in {
   def UseMovt          : Predicate<"Subtarget->useMovt(*MF)">;
   def DontUseMovt      : Predicate<"!Subtarget->useMovt(*MF)">;
+  def UseMovtInPic          : Predicate<"Subtarget->useMovt(*MF) && Subtarget->allowPositionIndependentMovt()">;
+  def DontUseMovtInPic      : Predicate<"!Subtarget->useMovt(*MF) || !Subtarget->allowPositionIndependentMovt()">;
 }
 def UseFPVMLx        : Predicate<"Subtarget->useFPVMLx()">;
 def UseMulOps        : Predicate<"Subtarget->useMulOps()">;
@@ -5644,26 +5646,26 @@ let isReMaterializable = 1 in {
 def MOV_ga_pcrel : PseudoInst<(outs GPR:$dst), (ins i32imm:$addr),
                               IIC_iMOVix2addpc,
                         [(set GPR:$dst, (ARMWrapperPIC tglobaladdr:$addr))]>,
-                        Requires<[IsARM, UseMovt]>;
+                        Requires<[IsARM, UseMovtInPic]>;
 
 def LDRLIT_ga_pcrel : PseudoInst<(outs GPR:$dst), (ins i32imm:$addr),
                                  IIC_iLoadiALU,
                                  [(set GPR:$dst,
                                        (ARMWrapperPIC tglobaladdr:$addr))]>,
-                      Requires<[IsARM, DontUseMovt]>;
+                      Requires<[IsARM, DontUseMovtInPic]>;
 
 let AddedComplexity = 10 in
 def LDRLIT_ga_pcrel_ldr : PseudoInst<(outs GPR:$dst), (ins i32imm:$addr),
                               NoItinerary,
                               [(set GPR:$dst,
                                     (load (ARMWrapperPIC tglobaladdr:$addr)))]>,
-                          Requires<[IsARM, DontUseMovt]>;
+                          Requires<[IsARM, DontUseMovtInPic]>;
 
 let AddedComplexity = 10 in
 def MOV_ga_pcrel_ldr : PseudoInst<(outs GPR:$dst), (ins i32imm:$addr),
                                 IIC_iMOVix2ld,
                     [(set GPR:$dst, (load (ARMWrapperPIC tglobaladdr:$addr)))]>,
-                    Requires<[IsARM, UseMovt]>;
+                    Requires<[IsARM, UseMovtInPic]>;
 } // isReMaterializable
 
 // The many different faces of TLS access.
@@ -5676,15 +5678,15 @@ def : Pat<(ARMWrapper tglobaltlsaddr:$src),
       Requires<[IsARM, DontUseMovt]>;
 
 def : Pat<(ARMWrapperPIC tglobaltlsaddr:$addr),
-          (MOV_ga_pcrel tglobaltlsaddr:$addr)>, Requires<[IsARM, UseMovt]>;
+          (MOV_ga_pcrel tglobaltlsaddr:$addr)>, Requires<[IsARM, UseMovtInPic]>;
 
 def : Pat<(ARMWrapperPIC tglobaltlsaddr:$addr),
           (LDRLIT_ga_pcrel tglobaltlsaddr:$addr)>,
-      Requires<[IsARM, DontUseMovt]>;
+      Requires<[IsARM, DontUseMovtInPic]>;
 let AddedComplexity = 10 in
 def : Pat<(load (ARMWrapperPIC tglobaltlsaddr:$addr)),
           (MOV_ga_pcrel_ldr tglobaltlsaddr:$addr)>,
-      Requires<[IsARM, UseMovt]>;
+      Requires<[IsARM, UseMovtInPic]>;
 
 
 // ConstantPool, GlobalAddress, and JumpTable
diff --git a/lib/Target/ARM/ARMInstrThumb.td b/lib/Target/ARM/ARMInstrThumb.td
index d6b9a21c2b8..c2bcc087e07 100644
--- a/lib/Target/ARM/ARMInstrThumb.td
+++ b/lib/Target/ARM/ARMInstrThumb.td
@@ -1509,7 +1509,7 @@ def tLDRLIT_ga_pcrel : PseudoInst<(outs tGPR:$dst), (ins i32imm:$addr),
                                   IIC_iLoadiALU,
                                   [(set tGPR:$dst,
                                         (ARMWrapperPIC tglobaladdr:$addr))]>,
-                       Requires<[IsThumb, DontUseMovt]>;
+                       Requires<[IsThumb, DontUseMovtInPic]>;
 
 def tLDRLIT_ga_abs : PseudoInst<(outs tGPR:$dst), (ins i32imm:$src),
                                 IIC_iLoad_i,
@@ -1520,7 +1520,7 @@ def tLDRLIT_ga_abs : PseudoInst<(outs tGPR:$dst), (ins i32imm:$src),
 // TLS globals
 def : Pat<(ARMWrapperPIC tglobaltlsaddr:$addr),
           (tLDRLIT_ga_pcrel tglobaltlsaddr:$addr)>,
-      Requires<[IsThumb, DontUseMovt]>;
+      Requires<[IsThumb, DontUseMovtInPic]>;
 def : Pat<(ARMWrapper tglobaltlsaddr:$addr),
           (tLDRLIT_ga_abs tglobaltlsaddr:$addr)>,
       Requires<[IsThumb, DontUseMovt]>;
diff --git a/lib/Target/ARM/ARMInstrThumb2.td b/lib/Target/ARM/ARMInstrThumb2.td
index f61cdc563d7..670ed127da7 100644
--- a/lib/Target/ARM/ARMInstrThumb2.td
+++ b/lib/Target/ARM/ARMInstrThumb2.td
@@ -3843,13 +3843,13 @@ let isReMaterializable = 1 in {
 def t2MOV_ga_pcrel : PseudoInst<(outs rGPR:$dst), (ins i32imm:$addr),
                                 IIC_iMOVix2addpc,
                           [(set rGPR:$dst, (ARMWrapperPIC tglobaladdr:$addr))]>,
-                          Requires<[IsThumb, HasV8MBaseline, UseMovt]>;
+                          Requires<[IsThumb, HasV8MBaseline, UseMovtInPic]>;
 
 }
 
 def : T2Pat<(ARMWrapperPIC tglobaltlsaddr :$dst),
             (t2MOV_ga_pcrel tglobaltlsaddr:$dst)>,
-      Requires<[IsThumb2, UseMovt]>;
+      Requires<[IsThumb2, UseMovtInPic]>;
 def : T2Pat<(ARMWrapper tglobaltlsaddr:$dst),
             (t2MOVi32imm tglobaltlsaddr:$dst)>,
       Requires<[IsThumb2, UseMovt]>;
diff --git a/lib/Target/ARM/ARMInstructionSelector.cpp b/lib/Target/ARM/ARMInstructionSelector.cpp
index fc61fd85670..aee3d850c02 100644
--- a/lib/Target/ARM/ARMInstructionSelector.cpp
+++ b/lib/Target/ARM/ARMInstructionSelector.cpp
@@ -538,8 +538,12 @@ bool ARMInstructionSelector::selectGlobal(MachineInstrBuilder &MIB,
             : (Indirect ? ARM::LDRLIT_ga_pcrel_ldr : ARM::LDRLIT_ga_pcrel);
     MIB->setDesc(TII.get(Opc));
 
+    int TargetFlags = ARMII::MO_NO_FLAG;
     if (STI.isTargetDarwin())
-      MIB->getOperand(1).setTargetFlags(ARMII::MO_NONLAZY);
+      TargetFlags |= ARMII::MO_NONLAZY;
+    if (STI.isGVInGOT(GV))
+      TargetFlags |= ARMII::MO_GOT;
+    MIB->getOperand(1).setTargetFlags(TargetFlags);
 
     if (Indirect)
       MIB.addMemOperand(MF.getMachineMemOperand(
diff --git a/lib/Target/ARM/ARMSubtarget.cpp b/lib/Target/ARM/ARMSubtarget.cpp
index a8546ec40a6..7e107e4f8fd 100644
--- a/lib/Target/ARM/ARMSubtarget.cpp
+++ b/lib/Target/ARM/ARMSubtarget.cpp
@@ -344,11 +344,9 @@ bool ARMSubtarget::isGVIndirectSymbol(const GlobalValue *GV) const {
   return false;
 }
 
-ARMCP::ARMCPModifier ARMSubtarget::getCPModifier(const GlobalValue *GV) const {
-  if (isTargetELF() && TM.isPositionIndependent() &&
-      !TM.shouldAssumeDSOLocal(*GV->getParent(), GV))
-    return ARMCP::GOT_PREL;
-  return ARMCP::no_modifier;
+bool ARMSubtarget::isGVInGOT(const GlobalValue *GV) const {
+  return isTargetELF() && TM.isPositionIndependent() &&
+         !TM.shouldAssumeDSOLocal(*GV->getParent(), GV);
 }
 
 unsigned ARMSubtarget::getMispredictionPenalty() const {
diff --git a/lib/Target/ARM/ARMSubtarget.h b/lib/Target/ARM/ARMSubtarget.h
index c57c4e7dcd3..4b4a44f2fe2 100644
--- a/lib/Target/ARM/ARMSubtarget.h
+++ b/lib/Target/ARM/ARMSubtarget.h
@@ -752,7 +752,7 @@ public:
   bool isGVIndirectSymbol(const GlobalValue *GV) const;
 
   /// Returns the constant pool modifier needed to access the GV.
-  ARMCP::ARMCPModifier getCPModifier(const GlobalValue *GV) const;
+  bool isGVInGOT(const GlobalValue *GV) const;
 
   /// True if fast-isel is used.
   bool useFastISel() const;
@@ -767,6 +767,13 @@ public:
       return ARM::BX_RET;
     return ARM::MOVPCLR;
   }
+
+  /// Allow movt+movw for PIC global address calculation.
+  /// ELF does not have GOT relocations for movt+movw.
+  /// ROPI does not use GOT.
+  bool allowPositionIndependentMovt() const {
+    return isROPI() || !isTargetELF();
+  }
 };
 
 } // end namespace llvm
diff --git a/lib/Target/ARM/MCTargetDesc/ARMBaseInfo.h b/lib/Target/ARM/MCTargetDesc/ARMBaseInfo.h
index 17da82b4ca3..c4480e3da50 100644
--- a/lib/Target/ARM/MCTargetDesc/ARMBaseInfo.h
+++ b/lib/Target/ARM/MCTargetDesc/ARMBaseInfo.h
@@ -228,7 +228,10 @@ namespace ARMII {
 
     /// MO_OPTION_MASK - Most flags are mutually exclusive; this mask selects
     /// just that part of the flag set.
-    MO_OPTION_MASK = 0x0f,
+    MO_OPTION_MASK = 0x3,
+
+    /// MO_GOT - On a symbol operand, this represents a GOT relative relocation.
+    MO_GOT = 0x8,
 
     /// MO_SBREL - On a symbol operand, this represents a static base relative
     /// relocation. Used in movw and movt instructions.
diff --git a/test/CodeGen/ARM/GlobalISel/arm-select-globals-pic.mir b/test/CodeGen/ARM/GlobalISel/arm-select-globals-pic.mir
index 3ef1b61211c..448a7f86e88 100644
--- a/test/CodeGen/ARM/GlobalISel/arm-select-globals-pic.mir
+++ b/test/CodeGen/ARM/GlobalISel/arm-select-globals-pic.mir
@@ -56,7 +56,7 @@ body:             |
     %0(p0) = G_GLOBAL_VALUE @external_global
     ; DARWIN-MOVT: [[G:%[0-9]+]]:gpr = MOV_ga_pcrel_ldr {{.*}} @external_global :: (load 4 from got)
     ; DARWIN-NOMOVT: [[G:%[0-9]+]]:gpr = LDRLIT_ga_pcrel_ldr {{.*}}@external_global :: (load 4 from got)
-    ; ELF: [[G:%[0-9]+]]:gpr = LDRLIT_ga_pcrel_ldr @external_global :: (load 4 from got)
+    ; ELF: [[G:%[0-9]+]]:gpr = LDRLIT_ga_pcrel_ldr target-flags(<unknown>) @external_global :: (load 4 from got)
 
     %1(s32) = G_LOAD %0(p0) :: (load 4 from @external_global)
     ; CHECK: [[V:%[0-9]+]]:gpr = LDRi12 [[G]], 0, 14, _ :: (load 4 from @external_global)
@@ -108,7 +108,7 @@ body:             |
     %0(p0) = G_GLOBAL_VALUE @external_constant
     ; DARWIN-MOVT: [[G:%[0-9]+]]:gpr = MOV_ga_pcrel_ldr {{.*}} @external_constant :: (load 4 from got)
     ; DARWIN-NOMOVT: [[G:%[0-9]+]]:gpr = LDRLIT_ga_pcrel_ldr {{.*}}@external_constant :: (load 4 from got)
-    ; ELF: [[G:%[0-9]+]]:gpr = LDRLIT_ga_pcrel_ldr @external_constant :: (load 4 from got)
+    ; ELF: [[G:%[0-9]+]]:gpr = LDRLIT_ga_pcrel_ldr target-flags(<unknown>) @external_constant :: (load 4 from got)
 
     %1(s32) = G_LOAD %0(p0) :: (load 4 from @external_constant)
     ; CHECK: [[V:%[0-9]+]]:gpr = LDRi12 [[G]], 0, 14, _ :: (load 4 from @external_constant)
diff --git a/test/CodeGen/ARM/load-global2.ll b/test/CodeGen/ARM/load-global2.ll
new file mode 100644
index 00000000000..7ffd65ce7ed
--- /dev/null
+++ b/test/CodeGen/ARM/load-global2.ll
@@ -0,0 +1,30 @@
+; PR35221. Test that external global address is not reloaded from GOT in each BB.
+; RUN: llc < %s -mtriple=armv7-linux-gnueabi -relocation-model=pic | FileCheck %s -check-prefix=LINUX-PIC
+
+@x = external global i8, align 1
+
+define signext i8 @foo() {
+entry:
+; LINUX-PIC:     ldr	r[[A:.]], .LCPI0_0
+; LINUX-PIC:     ldr	r[[B:.]], [pc, r[[A]]]
+; LINUX-PIC:     ldrb	r{{.}}, [r[[B]]]
+  %0 = load i8, i8* @x
+  %tobool = icmp eq i8 %0, 0
+  br i1 %tobool, label %bb1, label %bb2
+
+bb1:
+  call void @bar()
+; No more pc-relative loads! Reuse r[[B]].
+; LINUX-PIC:     bl	bar
+; LINUX-PIC-NOT: ldr{{.*}}[pc,
+; LINUX-PIC:     ldrsb	r{{.}}, [r[[B]]]
+  %1 = load i8, i8* @x
+  ret i8 %1
+
+bb2:
+  ret i8 0
+}
+
+declare void @bar()
+
+
diff --git a/test/CodeGen/Thumb2/v8_IT_3.ll b/test/CodeGen/Thumb2/v8_IT_3.ll
index 78b51a03308..dfa379e1f81 100644
--- a/test/CodeGen/Thumb2/v8_IT_3.ll
+++ b/test/CodeGen/Thumb2/v8_IT_3.ll
@@ -55,7 +55,11 @@ bb4:
 ; CHECK-PIC: cmp
 ; CHECK-PIC: cmp
 ; CHECK-PIC: cmp
-; CHECK-PIC-NEXT: bne
+; CHECK-PIC: it eq
+; CHECK-PIC-NEXT: ldreq
+; CHECK-PIC-NEXT: it eq
+; CHECK-PIC-NEXT: cmpeq
+; CHECK-PIC-NEXT: beq
 ; CHECK-PIC: %bb6
 ; CHECK-PIC-NEXT: movs
 ; CHECK-PIC-NEXT: add