[ARM] Fixup the creation of VPT blocks

This attempts to just fix the creation of VPT blocks, fixing up the iterating,
which instructions are considered in the bundle, and making sure that we do not
overrun the end of the block.

Differential Revision: https://reviews.llvm.org/D67219

llvm-svn: 371064

1 files changed, 20 insertions, 15 deletions

diff --git a/llvm/lib/Target/ARM/MVEVPTBlockPass.cpp b/llvm/lib/Target/ARM/MVEVPTBlockPass.cpp
index 78061170541..bfd7d37dfc8 100644
--- a/llvm/lib/Target/ARM/MVEVPTBlockPass.cpp
+++ b/llvm/lib/Target/ARM/MVEVPTBlockPass.cpp
@@ -82,8 +82,8 @@ enum VPTMaskValue {
 
 bool MVEVPTBlock::InsertVPTBlocks(MachineBasicBlock &Block) {
   bool Modified = false;
-  MachineBasicBlock::iterator MBIter = Block.begin();
-  MachineBasicBlock::iterator EndIter = Block.end();
+  MachineBasicBlock::instr_iterator MBIter = Block.instr_begin();
+  MachineBasicBlock::instr_iterator EndIter = Block.instr_end();
 
   while (MBIter != EndIter) {
     MachineInstr *MI = &*MBIter;
@@ -105,18 +105,27 @@ bool MVEVPTBlock::InsertVPTBlocks(MachineBasicBlock &Block) {
       continue;
     }
 
-    MachineInstrBuilder MIBuilder =
-        BuildMI(Block, MBIter, dl, TII->get(ARM::MVE_VPST));
-
-    MachineBasicBlock::iterator VPSTInsertPos = MIBuilder.getInstr();
+    LLVM_DEBUG(dbgs() << "VPT block created for: "; MI->dump());
     int VPTInstCnt = 1;
     ARMVCC::VPTCodes NextPred;
 
-    do {
-      ++MBIter;
+    // Look at subsequent instructions, checking if they can be in the same VPT
+    // block.
+    ++MBIter;
+    while (MBIter != EndIter && VPTInstCnt < 4) {
       NextPred = getVPTInstrPredicate(*MBIter, PredReg);
-    } while (NextPred != ARMVCC::None && NextPred == Pred && ++VPTInstCnt < 4);
+      assert(NextPred != ARMVCC::Else &&
+             "VPT block pass does not expect Else preds");
+      if (NextPred != Pred)
+        break;
+      LLVM_DEBUG(dbgs() << "  adding : "; MBIter->dump());
+      ++VPTInstCnt;
+      ++MBIter;
+    };
 
+    // Create the new VPST
+    MachineInstrBuilder MIBuilder =
+        BuildMI(Block, MI, dl, TII->get(ARM::MVE_VPST));
     switch (VPTInstCnt) {
     case 1:
       MIBuilder.addImm(VPTMaskValue::T);
@@ -134,14 +143,10 @@ bool MVEVPTBlock::InsertVPTBlocks(MachineBasicBlock &Block) {
       llvm_unreachable("Unexpected number of instruction in a VPT block");
     };
 
-    MachineInstr *LastMI = &*MBIter;
-    finalizeBundle(Block, VPSTInsertPos.getInstrIterator(),
-                   ++LastMI->getIterator());
+    finalizeBundle(
+        Block, MachineBasicBlock::instr_iterator(MIBuilder.getInstr()), MBIter);
 
     Modified = true;
-    LLVM_DEBUG(dbgs() << "VPT block created for: "; MI->dump());
-
-    ++MBIter;
   }
   return Modified;
 }