LiveRangeCalc: Don't start liveranges of PHI instruction at the block begin.

Summary:
Letting them begin at the PHI instruction slightly simplifies the code
but more importantly avoids breaking the assumption that live ranges
starting at the block begin are also live at the end of the predecessor
blocks. The MachineVerifier checks that but was apparently never run in
the few instances where liveranges are calculated for machine-SSA
functions.

Reviewers: qcolombet

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D7779

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230093 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/LiveRangeCalc.cpp b/lib/CodeGen/LiveRangeCalc.cpp
index a07c3a35dc7ae7b69570368fd581cb7b877173ae..d804b39c59775ed302ff43ea3068611da67b0415 100644 (file)
--- a/lib/CodeGen/LiveRangeCalc.cpp
+++ b/lib/CodeGen/LiveRangeCalc.cpp
@@ -43,11 +43,8 @@ void LiveRangeCalc::reset(const MachineFunction *mf,
 static void createDeadDef(SlotIndexes &Indexes, VNInfo::Allocator &Alloc,
                           LiveRange &LR, const MachineOperand &MO) {
     const MachineInstr *MI = MO.getParent();
-    SlotIndex DefIdx;
-    if (MI->isPHI())
-      DefIdx = Indexes.getMBBStartIdx(MI->getParent());
-    else
-      DefIdx = Indexes.getInstructionIndex(MI).getRegSlot(MO.isEarlyClobber());
+    SlotIndex DefIdx =
+        Indexes.getInstructionIndex(MI).getRegSlot(MO.isEarlyClobber());
 
     // Create the def in LR. This may find an existing def.
     LR.createDeadDef(DefIdx, Alloc);