[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

1 files changed, 13 insertions, 3 deletions

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 &,