[mips][FastISel] Instantiate the MipsFastISel class only for targets that support FastISel.

Summary:
Instead of instantiating the MipsFastISel class and checking if the
target is supported in the overriden methods, we should perform that
check before creating the class. This allows us to enable FastISel *only*
for targets that truly support it, ie. MIPS32 to MIPS32R5.

Reviewers: sdardis

Subscribers: ehostunreach, llvm-commits

Differential Revision: https://reviews.llvm.org/D24824

llvm-svn: 284475

2 files changed, 13 insertions, 22 deletions

diff --git a/llvm/lib/Target/Mips/MipsFastISel.cpp b/llvm/lib/Target/Mips/MipsFastISel.cpp
index 1581bc9c58a..895d0f7a607 100644
--- a/llvm/lib/Target/Mips/MipsFastISel.cpp
+++ b/llvm/lib/Target/Mips/MipsFastISel.cpp
@@ -102,7 +102,6 @@ class MipsFastISel final : public FastISel {
   bool fastLowerCall(CallLoweringInfo &CLI) override;
   bool fastLowerIntrinsicCall(const IntrinsicInst *II) override;
 
-  bool TargetSupported;
   bool UnsupportedFPMode; // To allow fast-isel to proceed and just not handle
   // floating point but not reject doing fast-isel in other
   // situations
@@ -212,10 +211,6 @@ public:
         TII(*Subtarget->getInstrInfo()), TLI(*Subtarget->getTargetLowering()) {
     MFI = funcInfo.MF->getInfo<MipsFunctionInfo>();
     Context = &funcInfo.Fn->getContext();
-    bool ISASupported = !Subtarget->hasMips32r6() &&
-                        !Subtarget->inMicroMipsMode() && Subtarget->hasMips32();
-    TargetSupported =
-        ISASupported && TM.isPositionIndependent() && getABI().IsO32();
     UnsupportedFPMode = Subtarget->isFP64bit() || Subtarget->useSoftFloat();
   }
 
@@ -291,9 +286,6 @@ unsigned MipsFastISel::emitLogicalOp(unsigned ISDOpc, MVT RetVT,
 }
 
 unsigned MipsFastISel::fastMaterializeAlloca(const AllocaInst *AI) {
-  if (!TargetSupported)
-    return 0;
-
   assert(TLI.getValueType(DL, AI->getType(), true) == MVT::i32 &&
          "Alloca should always return a pointer.");
 
@@ -404,9 +396,6 @@ unsigned MipsFastISel::materializeExternalCallSym(MCSymbol *Sym) {
 // Materialize a constant into a register, and return the register
 // number (or zero if we failed to handle it).
 unsigned MipsFastISel::fastMaterializeConstant(const Constant *C) {
-  if (!TargetSupported)
-    return 0;
-
   EVT CEVT = TLI.getValueType(DL, C->getType(), true);
 
   // Only handle simple types.
@@ -1444,9 +1433,6 @@ bool MipsFastISel::fastLowerArguments() {
 }
 
 bool MipsFastISel::fastLowerCall(CallLoweringInfo &CLI) {
-  if (!TargetSupported)
-    return false;
-
   CallingConv::ID CC = CLI.CallConv;
   bool IsTailCall = CLI.IsTailCall;
   bool IsVarArg = CLI.IsVarArg;
@@ -1531,9 +1517,6 @@ bool MipsFastISel::fastLowerCall(CallLoweringInfo &CLI) {
 }
 
 bool MipsFastISel::fastLowerIntrinsicCall(const IntrinsicInst *II) {
-  if (!TargetSupported)
-    return false;
-
   switch (II->getIntrinsicID()) {
   default:
     return false;
@@ -1980,8 +1963,6 @@ bool MipsFastISel::selectShift(const Instruction *I) {
 }
 
 bool MipsFastISel::fastSelectInstruction(const Instruction *I) {
-  if (!TargetSupported)
-    return false;
   switch (I->getOpcode()) {
   default:
     break;
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index fcd0450a067..be98b58fc2f 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -458,9 +458,19 @@ const MipsTargetLowering *MipsTargetLowering::create(const MipsTargetMachine &TM
 FastISel *
 MipsTargetLowering::createFastISel(FunctionLoweringInfo &funcInfo,
                                   const TargetLibraryInfo *libInfo) const {
-  if (!funcInfo.MF->getTarget().Options.EnableFastISel)
-    return TargetLowering::createFastISel(funcInfo, libInfo);
-  return Mips::createFastISel(funcInfo, libInfo);
+  const MipsTargetMachine &TM =
+      static_cast<const MipsTargetMachine &>(funcInfo.MF->getTarget());
+
+  // We support only the standard encoding [MIPS32,MIPS32R5] ISAs.
+  bool UseFastISel = TM.Options.EnableFastISel && Subtarget.hasMips32() &&
+                     !Subtarget.hasMips32r6() && !Subtarget.inMips16Mode() &&
+                     !Subtarget.inMicroMipsMode();
+
+  // Disable if we don't generate PIC or the ABI isn't O32.
+  if (!TM.isPositionIndependent() || !TM.getABI().IsO32())
+    UseFastISel = false;
+
+  return UseFastISel ? Mips::createFastISel(funcInfo, libInfo) : nullptr;
 }
 
 EVT MipsTargetLowering::getSetCCResultType(const DataLayout &, LLVMContext &,