AMDGPU/GlobalISel: Fix processing new phi in waterfall loop

The adjusted iterator range included the last we just inserted, and
don't want to process. Figure out the new iterator range before
inserting phis. This was a harmless problem, but added an unnecessary
complication for a future patch.

diff --git a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
index 4943f99..0fe2fcb 100644 (file)
--- a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
@@ -762,6 +762,10 @@ bool AMDGPURegisterBankInfo::executeInWaterfallLoop(
   const unsigned ExecReg =  Subtarget.isWave32() ?
     AMDGPU::EXEC_LO : AMDGPU::EXEC;
 
+#ifndef NDEBUG
+  const int OrigRangeSize = std::distance(Range.begin(), Range.end());
+#endif
+
   for (MachineInstr &MI : Range) {
     for (MachineOperand &Def : MI.defs()) {
       LLT ResTy = MRI.getType(Def.getReg());
@@ -827,13 +831,14 @@ bool AMDGPURegisterBankInfo::executeInWaterfallLoop(
 
   const DebugLoc &DL = B.getDL();
 
-  // Figure out the iterator range after splicing the instructions.
-  auto NewBegin = std::prev(LoopBB->end());
+  MachineInstr &FirstInst = *Range.begin();
 
   // Move the instruction into the loop. Note we moved everything after
   // Range.end() already into a new block, so Range.end() is no longer valid.
   LoopBB->splice(LoopBB->end(), &MBB, Range.begin(), MBB.end());
 
+  // Figure out the iterator range after splicing the instructions.
+  MachineBasicBlock::iterator NewBegin = FirstInst.getIterator();
   auto NewEnd = LoopBB->end();
 
   MachineBasicBlock::iterator I = Range.begin();
@@ -841,6 +846,8 @@ bool AMDGPURegisterBankInfo::executeInWaterfallLoop(
 
   Register CondReg;
 
+  assert(std::distance(NewBegin, NewEnd) == OrigRangeSize);
+
   for (MachineInstr &MI : make_range(NewBegin, NewEnd)) {
     for (MachineOperand &Op : MI.uses()) {
       if (!Op.isReg() || Op.isDef())