6 files changed, 89 insertions, 6 deletions
diff --git a/llvm/lib/Target/AMDGPU/SIDefines.h b/llvm/lib/Target/AMDGPU/SIDefines.h
index 759a043d7e9..3c8a790ffb4 100644
--- a/llvm/lib/Target/AMDGPU/SIDefines.h
+++ b/llvm/lib/Target/AMDGPU/SIDefines.h
@@ -65,8 +65,8 @@ enum : uint64_t {
   SOPK_ZEXT = UINT64_C(1) << 38,
   SCALAR_STORE = UINT64_C(1) << 39,
   FIXED_SIZE = UINT64_C(1) << 40,
-  VOPAsmPrefer32Bit = UINT64_C(1) << 41
-
+  VOPAsmPrefer32Bit = UINT64_C(1) << 41,
+  HasFPClamp = UINT64_C(1) << 42
 };
 
 // v_cmp_class_* etc. use a 10-bit mask for what operation is checked.
diff --git a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
index a5c0d4923d6..f223f57bfa3 100644
--- a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
@@ -66,6 +66,7 @@ public:
   MachineRegisterInfo *MRI;
   const SIInstrInfo *TII;
   const SIRegisterInfo *TRI;
+  const SISubtarget *ST;
 
   void foldOperand(MachineOperand &OpToFold,
                    MachineInstr *UseMI,
@@ -75,6 +76,9 @@ public:
 
   void foldInstOperand(MachineInstr &MI, MachineOperand &OpToFold) const;
 
+  const MachineOperand *isClamp(const MachineInstr &MI) const;
+  bool tryFoldClamp(MachineInstr &MI);
+
 public:
   SIFoldOperands() : MachineFunctionPass(ID) {
     initializeSIFoldOperandsPass(*PassRegistry::getPassRegistry());
@@ -686,14 +690,75 @@ void SIFoldOperands::foldInstOperand(MachineInstr &MI,
   }
 }
 
+const MachineOperand *SIFoldOperands::isClamp(const MachineInstr &MI) const {
+  unsigned Op = MI.getOpcode();
+  switch (Op) {
+  case AMDGPU::V_MAX_F32_e64:
+  case AMDGPU::V_MAX_F16_e64: {
+    if (!TII->getNamedOperand(MI, AMDGPU::OpName::clamp)->getImm())
+      return nullptr;
+
+    // Make sure sources are identical.
+    const MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
+    const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
+    if (!Src0->isReg() || Src0->getSubReg() != Src1->getSubReg() ||
+        Src0->getSubReg() != AMDGPU::NoSubRegister)
+      return nullptr;
+
+    // Can't fold up if we have modifiers.
+    if (TII->hasModifiersSet(MI, AMDGPU::OpName::src0_modifiers) ||
+        TII->hasModifiersSet(MI, AMDGPU::OpName::src1_modifiers) ||
+        TII->hasModifiersSet(MI, AMDGPU::OpName::omod))
+      return nullptr;
+    return Src0;
+  }
+  default:
+    return nullptr;
+  }
+}
+
+// We obviously have multiple uses in a clamp since the register is used twice
+// in the same instruction.
+static bool hasOneNonDBGUseInst(const MachineRegisterInfo &MRI, unsigned Reg) {
+  int Count = 0;
+  for (auto I = MRI.use_instr_nodbg_begin(Reg), E = MRI.use_instr_nodbg_end();
+       I != E; ++I) {
+    if (++Count > 1)
+      return false;
+  }
+
+  return true;
+}
+
+// FIXME: Does this need to check IEEE bit on function?
+bool SIFoldOperands::tryFoldClamp(MachineInstr &MI) {
+  const MachineOperand *ClampSrc = isClamp(MI);
+  if (!ClampSrc || !hasOneNonDBGUseInst(*MRI, ClampSrc->getReg()))
+    return false;
+
+  MachineInstr *Def = MRI->getVRegDef(ClampSrc->getReg());
+  if (!TII->hasFPClamp(*Def))
+    return false;
+  MachineOperand *DefClamp = TII->getNamedOperand(*Def, AMDGPU::OpName::clamp);
+  if (!DefClamp)
+    return false;
+
+  DEBUG(dbgs() << "Folding clamp " << *DefClamp << " into " << *Def << '\n');
+
+  // Clamp is applied after omod, so it is OK if omod is set.
+  DefClamp->setImm(1);
+  MRI->replaceRegWith(MI.getOperand(0).getReg(), Def->getOperand(0).getReg());
+  MI.eraseFromParent();
+  return true;
+}
+
 bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
   if (skipFunction(*MF.getFunction()))
     return false;
 
-  const SISubtarget &ST = MF.getSubtarget<SISubtarget>();
-
   MRI = &MF.getRegInfo();
-  TII = ST.getInstrInfo();
+  ST = &MF.getSubtarget<SISubtarget>();
+  TII = ST->getInstrInfo();
   TRI = &TII->getRegisterInfo();
 
   for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
@@ -705,8 +770,11 @@ bool SIFoldOperands::runOnMachineFunction(MachineFunction &MF) {
       Next = std::next(I);
       MachineInstr &MI = *I;
 
-      if (!isSafeToFold(MI))
+      if (!isSafeToFold(MI)) {
+        // TODO: Try omod also.
+        tryFoldClamp(MI);
         continue;
+      }
 
       MachineOperand &OpToFold = MI.getOperand(1);
       bool FoldingImm = OpToFold.isImm() || OpToFold.isFI();
diff --git a/llvm/lib/Target/AMDGPU/SIInstrFormats.td b/llvm/lib/Target/AMDGPU/SIInstrFormats.td
index 5523ec142ba..6da32785b23 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrFormats.td
+++ b/llvm/lib/Target/AMDGPU/SIInstrFormats.td
@@ -78,6 +78,10 @@ class InstSI <dag outs, dag ins, string asm = "",
   // is unable to infer the encoding from the operands.
   field bit VOPAsmPrefer32Bit = 0;
 
+  // This bit indicates that this has a floating point result type, so
+  // the clamp modifier has floating point semantics.
+  field bit FPClamp = 0;
+
   // These need to be kept in sync with the enum in SIInstrFlags.
   let TSFlags{0} = SALU;
   let TSFlags{1} = VALU;
@@ -120,6 +124,7 @@ class InstSI <dag outs, dag ins, string asm = "",
   let TSFlags{39} = ScalarStore;
   let TSFlags{40} = FixedSize;
   let TSFlags{41} = VOPAsmPrefer32Bit;
+  let TSFlags{42} = FPClamp;
 
   let SchedRW = [Write32Bit];
 
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.h b/llvm/lib/Target/AMDGPU/SIInstrInfo.h
index 5f53fd18917..ba59623a8e4 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.h
@@ -474,6 +474,14 @@ public:
     return get(Opcode).TSFlags & SIInstrFlags::FIXED_SIZE;
   }
 
+  static bool hasFPClamp(const MachineInstr &MI) {
+    return MI.getDesc().TSFlags & SIInstrFlags::HasFPClamp;
+  }
+
+  bool hasFPClamp(uint16_t Opcode) const {
+    return get(Opcode).TSFlags & SIInstrFlags::HasFPClamp;
+  }
+
   bool isVGPRCopy(const MachineInstr &MI) const {
     assert(MI.isCopy());
     unsigned Dest = MI.getOperand(0).getReg();
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.td b/llvm/lib/Target/AMDGPU/SIInstrInfo.td
index e832a0658d1..1c138feab43 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.td
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.td
@@ -1086,6 +1086,7 @@ class VOPProfile <list<ValueType> _ArgVT> {
   field bit HasOMod = HasModifiers;
   field bit HasClamp = HasModifiers;
   field bit HasSDWAClamp = HasSrc0;
+  field bit HasFPClamp = BitAnd<isFloatType<DstVT>.ret, HasClamp>.ret;
 
   field bit HasExt = getHasExt<NumSrcArgs, DstVT, Src0VT, Src1VT>.ret;
 
diff --git a/llvm/lib/Target/AMDGPU/VOPInstructions.td b/llvm/lib/Target/AMDGPU/VOPInstructions.td
index ebc01ffc3af..6ba3e12c29c 100644
--- a/llvm/lib/Target/AMDGPU/VOPInstructions.td
+++ b/llvm/lib/Target/AMDGPU/VOPInstructions.td
@@ -100,6 +100,7 @@ class VOP3_Pseudo <string opName, VOPProfile P, list<dag> pattern=[], bit VOP3On
 
   let VOP3 = 1;
   let VALU = 1;
+  let FPClamp = P.HasFPClamp;
   let Uses = [EXEC];
 
   let AsmVariantName = AMDGPUAsmVariants.VOP3;