[AMDGPU] Skip non-wwm reg implicit-def from bb prolog (#115834)

Currently all implicit-def instructions are part of
bb prolog. We should only include the wwm-register's
implicit definitions into the BB prolog. The other
vector class registers' implicit defs when exist at
the bb top might cause interference when pushed the
LR_split copy insertion downwards. The SplitKit is
very strict on altering the insertion points and will
assert such instances.

2 files changed, 9 insertions, 2 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index ad45af0..c864f03 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -8909,16 +8909,19 @@ bool SIInstrInfo::isBasicBlockPrologue(const MachineInstr &MI,
   // needed by the prolog. However, the insertions for scalar registers can
   // always be placed at the BB top as they are independent of the exec mask
   // value.
+  const MachineFunction *MF = MI.getParent()->getParent();
   bool IsNullOrVectorRegister = true;
   if (Reg) {
-    const MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
+    const MachineRegisterInfo &MRI = MF->getRegInfo();
     IsNullOrVectorRegister = !RI.isSGPRClass(RI.getRegClassForReg(MRI, Reg));
   }
 
   uint16_t Opcode = MI.getOpcode();
+  const SIMachineFunctionInfo *MFI = MF->getInfo<SIMachineFunctionInfo>();
   return IsNullOrVectorRegister &&
          (isSGPRSpill(Opcode) || isWWMRegSpillOpcode(Opcode) ||
-          Opcode == AMDGPU::IMPLICIT_DEF ||
+          (Opcode == AMDGPU::IMPLICIT_DEF &&
+           MFI->isWWMReg(MI.getOperand(0).getReg())) ||
           (!MI.isTerminator() && Opcode != AMDGPU::COPY &&
            MI.modifiesRegister(AMDGPU::EXEC, &RI)));
 }
diff --git a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
index 018322e..2a75468 100644
--- a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
@@ -596,6 +596,10 @@ public:
                                 SMDiagnostic &Error, SMRange &SourceRange);
 
   void reserveWWMRegister(Register Reg) { WWMReservedRegs.insert(Reg); }
+  bool isWWMReg(Register Reg) const {
+    return Reg.isVirtual() ? checkFlag(Reg, AMDGPU::VirtRegFlag::WWM_REG)
+                           : WWMReservedRegs.contains(Reg);
+  }
 
   void updateNonWWMRegMask(BitVector &RegMask) { NonWWMRegMask = RegMask; }
   BitVector getNonWWMRegMask() const { return NonWWMRegMask; }