[WinEH] Mark funclet entries and exits as clobbering all registers

Summary:
In this implementation, LiveIntervalAnalysis invents a few register
masks on basic block boundaries that preserve no registers. The nice
thing about this is that it prevents the prologue inserter from thinking
it needs to spill all XMM CSRs, because it doesn't see any explicit
physreg defs in the MI.

Reviewers: MatzeB, qcolombet, JosephTremoulet, majnemer

Subscribers: MatzeB, llvm-commits

Differential Revision: http://reviews.llvm.org/D14407

llvm-svn: 252318

5 files changed, 31 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index 8d9d984b5da..afd8db8d408 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -225,6 +225,13 @@ void LiveIntervals::computeRegMasks() {
   for (MachineBasicBlock &MBB : *MF) {
     std::pair<unsigned, unsigned> &RMB = RegMaskBlocks[MBB.getNumber()];
     RMB.first = RegMaskSlots.size();
+
+    // Some block starts, such as EH funclets, create masks.
+    if (const uint32_t *Mask = MBB.getBeginClobberMask(TRI)) {
+      RegMaskSlots.push_back(Indexes->getMBBStartIdx(&MBB));
+      RegMaskBits.push_back(Mask);
+    }
+
     for (MachineInstr &MI : MBB) {
       for (const MachineOperand &MO : MI.operands()) {
         if (!MO.isRegMask())
@@ -233,6 +240,13 @@ void LiveIntervals::computeRegMasks() {
         RegMaskBits.push_back(MO.getRegMask());
       }
     }
+
+    // Some block ends, such as funclet returns, create masks.
+    if (const uint32_t *Mask = MBB.getEndClobberMask(TRI)) {
+      RegMaskSlots.push_back(Indexes->getMBBEndIdx(&MBB));
+      RegMaskBits.push_back(Mask);
+    }
+
     // Compute the number of register mask instructions in this block.
     RMB.second = RegMaskSlots.size() - RMB.first;
   }
diff --git a/llvm/lib/CodeGen/MachineBasicBlock.cpp b/llvm/lib/CodeGen/MachineBasicBlock.cpp
index 1fdaf329075..8e11979ef1c 100644
--- a/llvm/lib/CodeGen/MachineBasicBlock.cpp
+++ b/llvm/lib/CodeGen/MachineBasicBlock.cpp
@@ -1301,3 +1301,17 @@ MachineBasicBlock::computeRegisterLiveness(const TargetRegisterInfo *TRI,
   // At this point we have no idea of the liveness of the register.
   return LQR_Unknown;
 }
+
+const uint32_t *
+MachineBasicBlock::getBeginClobberMask(const TargetRegisterInfo *TRI) const {
+  // EH funclet entry does not preserve any registers.
+  return isEHFuncletEntry() ? TRI->getNoPreservedMask() : nullptr;
+}
+
+const uint32_t *
+MachineBasicBlock::getEndClobberMask(const TargetRegisterInfo *TRI) const {
+  // If we see a return block with successors, this must be a funclet return,
+  // which does not preserve any registers. If there are no successors, we don't
+  // care what kind of return it is, putting a mask after it is a no-op.
+  return isReturnBlock() && !succ_empty() ? TRI->getNoPreservedMask() : nullptr;
+}
diff --git a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h
index d4b7c7be865..cea8b80c782 100644
--- a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h
+++ b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.h
@@ -94,7 +94,7 @@ public:
   const MCPhysReg *getCalleeSavedRegs(const MachineFunction *MF) const override;
   const uint32_t *getCallPreservedMask(const MachineFunction &MF,
                                        CallingConv::ID) const override;
-  const uint32_t *getNoPreservedMask() const;
+  const uint32_t *getNoPreservedMask() const override;
 
   /// getThisReturnPreservedMask - Returns a call preserved mask specific to the
   /// case that 'returned' is on an i32 first argument if the calling convention
diff --git a/llvm/lib/Target/PowerPC/PPCRegisterInfo.h b/llvm/lib/Target/PowerPC/PPCRegisterInfo.h
index 743ac53108b..1b1e160d836 100644
--- a/llvm/lib/Target/PowerPC/PPCRegisterInfo.h
+++ b/llvm/lib/Target/PowerPC/PPCRegisterInfo.h
@@ -77,7 +77,7 @@ public:
   const MCPhysReg *getCalleeSavedRegs(const MachineFunction *MF) const override;
   const uint32_t *getCallPreservedMask(const MachineFunction &MF,
                                        CallingConv::ID CC) const override;
-  const uint32_t *getNoPreservedMask() const;
+  const uint32_t *getNoPreservedMask() const override;
 
   void adjustStackMapLiveOutMask(uint32_t *Mask) const override;
 
diff --git a/llvm/lib/Target/X86/X86RegisterInfo.h b/llvm/lib/Target/X86/X86RegisterInfo.h
index f18d4d203bc..c20842b25de 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.h
+++ b/llvm/lib/Target/X86/X86RegisterInfo.h
@@ -96,7 +96,7 @@ public:
   getCalleeSavedRegs(const MachineFunction* MF) const override;
   const uint32_t *getCallPreservedMask(const MachineFunction &MF,
                                        CallingConv::ID) const override;
-  const uint32_t *getNoPreservedMask() const;
+  const uint32_t *getNoPreservedMask() const override;
 
   /// getReservedRegs - Returns a bitset indexed by physical register number
   /// indicating if a register is a special register that has particular uses and