[mips] Expand BuildPairF64 to a spill and reload when the O32 FPXX ABI is

enabled and mthc1 and dmtc1 are not available (e.g. on MIPS32r1)

This prevents the upper 32-bits of a double precision value from being moved to
the FPU with mtc1 to an odd-numbered FPU register. This is necessary to ensure
that the code generated executes correctly regardless of the current FPU mode.

MIPS32r2 and above continues to use mtc1/mthc1, while MIPS-IV and above continue
to use dmtc1.

Differential Revision: http://reviews.llvm.org/D4465

llvm-svn: 212930

1 files changed, 9 insertions, 10 deletions

diff --git a/llvm/lib/Target/Mips/MipsSEInstrInfo.cpp b/llvm/lib/Target/Mips/MipsSEInstrInfo.cpp
index 32da7492dad..aad401857c3 100644
--- a/llvm/lib/Target/Mips/MipsSEInstrInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsSEInstrInfo.cpp
@@ -547,29 +547,26 @@ void MipsSEInstrInfo::expandBuildPairF64(MachineBasicBlock &MBB,
   const MCInstrDesc& Mtc1Tdd = get(Mips::MTC1);
   DebugLoc dl = I->getDebugLoc();
   const TargetRegisterInfo &TRI = getRegisterInfo();
-  bool HasMTHC1 = TM.getSubtarget<MipsSubtarget>().hasMips32r2() ||
-                  TM.getSubtarget<MipsSubtarget>().hasMips32r6();
 
   // When mthc1 is available, use:
   //   mtc1 Lo, $fp
   //   mthc1 Hi, $fp
   //
-  // Otherwise, for FP64:
+  // Otherwise, for O32 FPXX ABI:
   //   spill + reload via ldc1
-  // This has not been implemented since FP64 on MIPS32 and earlier is not
-  // supported.
+  // This case is handled by the frame lowering code.
   //
   // Otherwise, for FP32:
   //   mtc1 Lo, $fp
   //   mtc1 Hi, $fp + 1
+  //
+  // The case where dmtc1 is available doesn't need to be handled here
+  // because it never creates a BuildPairF64 node.
 
   BuildMI(MBB, I, dl, Mtc1Tdd, TRI.getSubReg(DstReg, Mips::sub_lo))
     .addReg(LoReg);
 
-  if (HasMTHC1 || FP64) {
-    assert(TM.getSubtarget<MipsSubtarget>().hasMips32r2() &&
-           "MTHC1 requires MIPS32r2");
-
+  if (TM.getSubtarget<MipsSubtarget>().hasMTHC1()) {
     // FIXME: The .addReg(DstReg) is a white lie used to temporarily work
     //        around a widespread bug in the -mfp64 support.
     //        The problem is that none of the 32-bit fpu ops mention the fact
@@ -584,7 +581,9 @@ void MipsSEInstrInfo::expandBuildPairF64(MachineBasicBlock &MBB,
     BuildMI(MBB, I, dl, get(FP64 ? Mips::MTHC1_D64 : Mips::MTHC1_D32), DstReg)
         .addReg(DstReg)
         .addReg(HiReg);
-  } else
+  } else if (TM.getSubtarget<MipsSubtarget>().isABI_FPXX())
+    llvm_unreachable("BuildPairF64 not expanded in frame lowering code!");
+  else
     BuildMI(MBB, I, dl, Mtc1Tdd, TRI.getSubReg(DstReg, Mips::sub_hi))
       .addReg(HiReg);
 }