Rewrite the physreg part of findLastUseBefore().

To find the last use of a register unit, start from the bottom and scan
upwards until a user is found.

<rdar://problem/13353090>

llvm-svn: 176706

llvm/lib/CodeGen/LiveIntervalAnalysis.cpp

@@ -972,9 +972,9 @@ private:
 
   // Return the last use of reg between NewIdx and OldIdx.
   SlotIndex findLastUseBefore(unsigned Reg) {
-    SlotIndex LastUse = NewIdx;
 
     if (TargetRegisterInfo::isVirtualRegister(Reg)) {
+      SlotIndex LastUse = NewIdx;
       for (MachineRegisterInfo::use_nodbg_iterator
              UI = MRI.use_nodbg_begin(Reg),
              UE = MRI.use_nodbg_end();
@@ -984,30 +984,42 @@ private:
         if (InstSlot > LastUse && InstSlot < OldIdx)
           LastUse = InstSlot;
       }
-    } else {
+      return LastUse;
-      MachineInstr* MI = LIS.getSlotIndexes()->getInstructionFromIndex(NewIdx);
-      MachineBasicBlock::iterator MII(MI);
-      ++MII;
-      MachineBasicBlock* MBB = MI->getParent();
-      for (; MII != MBB->end(); ++MII){
-        if (MII->isDebugValue())
-          continue;
-        if (LIS.getInstructionIndex(MII) < OldIdx)
-          break;
-        for (MachineInstr::mop_iterator MOI = MII->operands_begin(),
-                                        MOE = MII->operands_end();
-             MOI != MOE; ++MOI) {
-          const MachineOperand& mop = *MOI;
-          if (!mop.isReg() || mop.getReg() == 0 ||
-              TargetRegisterInfo::isVirtualRegister(mop.getReg()))
-            continue;
-
-          if (TRI.hasRegUnit(mop.getReg(), Reg))
-            LastUse = LIS.getInstructionIndex(MII);
-        }
-      }
     }
-    return LastUse;
+
+    // This is a regunit interval, so scanning the use list could be very
+    // expensive. Scan upwards from OldIdx instead.
+    assert(NewIdx < OldIdx && "Expected upwards move");
+    SlotIndexes *Indexes = LIS.getSlotIndexes();
+    MachineBasicBlock *MBB = Indexes->getMBBFromIndex(NewIdx);
+
+    // OldIdx may not correspond to an instruction any longer, so set MII to
+    // point to the next instruction after OldIdx, or MBB->end().
+    MachineBasicBlock::iterator MII = MBB->end();
+    if (MachineInstr *MI = Indexes->getInstructionFromIndex(
+                           Indexes->getNextNonNullIndex(OldIdx)))
+      if (MI->getParent() == MBB)
+        MII = MI;
+
+    MachineBasicBlock::iterator Begin = MBB->begin();
+    while (MII != Begin) {
+      if ((--MII)->isDebugValue())
+        continue;
+      SlotIndex Idx = Indexes->getInstructionIndex(MII);
+
+      // Stop searching when NewIdx is reached.
+      if (!SlotIndex::isEarlierInstr(NewIdx, Idx))
+        return NewIdx;
+
+      // Check if MII uses Reg.
+      for (MIBundleOperands MO(MII); MO.isValid(); ++MO)
+        if (MO->isReg() &&
+            TargetRegisterInfo::isPhysicalRegister(MO->getReg()) &&
+            TRI.hasRegUnit(MO->getReg(), Reg))
+          return Idx;
+    }
+    // Didn't reach NewIdx. It must be the first instruction in the block.
+    return NewIdx;
   }
 };
 

llvm/test/CodeGen/X86/misched-crash.ll

@@ -0,0 +1,40 @@
+; RUN: llc < %s -enable-misched -verify-misched
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10"
+
+; This function contains a cmp instruction with two users.
+; Hoisting the last use requires trimming the EFLAGS live range to the second.
+define void @rdar13353090(i8* %plane, i64 %_x1, i64 %_x2) {
+entry:
+  %cmp = icmp ult i64 %_x1, %_x2
+  %cond = select i1 %cmp, i64 %_x1, i64 %_x2
+  %cond10 = select i1 %cmp, i64 %_x2, i64 %_x1
+  %0 = load i64* null, align 8
+  %cmp16 = icmp ult i64 %cond, %0
+  %cmp23 = icmp ugt i64 %cond10, 0
+  br i1 %cmp16, label %land.lhs.true21, label %return
+
+land.lhs.true21:                                  ; preds = %entry
+  %sub = add i64 %0, -1
+  br i1 %cmp23, label %if.then24, label %return
+
+if.then24:                                        ; preds = %land.lhs.true21
+  %cmp16.i = icmp ult i64 %cond, %sub
+  %cond20.i = select i1 %cmp16.i, i64 %cond, i64 %sub
+  %add21.i = add i64 0, %cond20.i
+  br label %for.body34.i
+
+for.body34.i:                                     ; preds = %for.inc39.i, %if.then24
+  %index.178.i = phi i64 [ %add21.i, %if.then24 ], [ %inc41.i, %for.inc39.i ]
+  %arrayidx35.i = getelementptr inbounds i8* %plane, i64 %index.178.i
+  %1 = load i8* %arrayidx35.i, align 1
+  %tobool36.i = icmp eq i8 %1, 0
+  br i1 %tobool36.i, label %for.inc39.i, label %return
+
+for.inc39.i:                                      ; preds = %for.body34.i
+  %inc41.i = add i64 %index.178.i, 1
+  br i1 undef, label %return, label %for.body34.i
+
+return:                                           ; preds = %for.inc39.i, %for.body34.i, %land.lhs.true21, %entry
+  ret void
+}