Check loop exit predicate properly while eliminating one iteration loop.

This patch fixes PR 2869


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57369 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopIndexSplit.cpp

@@ -585,16 +585,7 @@ bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
   // only when index variable is equal to split value.
   IndVar->replaceAllUsesWith(SD.SplitValue);
 
-  // Remove Latch to Header edge.
-  BasicBlock *LatchSucc = NULL;
-  Header->removePredecessor(Latch);
-  for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
-       SI != E; ++SI) {
-    if (Header != *SI)
-      LatchSucc = *SI;
-  }
-  BR->setUnconditionalDest(LatchSucc);
-
+  Instruction *LTerminator = Latch->getTerminator();
   Instruction *Terminator = Header->getTerminator();
   Value *ExitValue = ExitCondition->getOperand(ExitValueNum);
 
@@ -606,22 +597,33 @@ bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
   //      c2 = icmp ult i32 SplitValue, ExitValue
   //      and i32 c1, c2 
   bool SignedPredicate = ExitCondition->isSignedPredicate();
+  CmpInst::Predicate C2Predicate = ExitCondition->getPredicate();
+  if (LTerminator->getOperand(0) != Header)
+    C2Predicate = CmpInst::getInversePredicate(C2Predicate);
   Instruction *C1 = new ICmpInst(SignedPredicate ? 
                                  ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
                                  SD.SplitValue, StartValue, "lisplit", 
                                  Terminator);
-  Instruction *C2 = new ICmpInst(SignedPredicate ? 
-                                 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
+  Instruction *C2 = new ICmpInst(C2Predicate,
                                  SD.SplitValue, ExitValue, "lisplit", 
                                  Terminator);
   Instruction *NSplitCond = BinaryOperator::CreateAnd(C1, C2, "lisplit", 
                                                       Terminator);
   SD.SplitCondition->replaceAllUsesWith(NSplitCond);
   SD.SplitCondition->eraseFromParent();
 
+  // Remove Latch to Header edge.
+  BasicBlock *LatchSucc = NULL;
+  Header->removePredecessor(Latch);
+  for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
+       SI != E; ++SI) {
+    if (Header != *SI)
+      LatchSucc = *SI;
+  }
+  BR->setUnconditionalDest(LatchSucc);
+
   // Now, clear latch block. Remove instructions that are responsible
   // to increment induction variable. 
-  Instruction *LTerminator = Latch->getTerminator();
   for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end();
        LB != LE; ) {
     Instruction *I = LB;

test/Transforms/LoopIndexSplit/2008-10-10-OneIteration.ll

@@ -0,0 +1,66 @@
+; RUN: llvm-as < %s | opt -loop-index-split | llvm-dis | grep sle | count 1
+; PR 2869
+
+@w = external global [2 x [2 x i32]]		; <[2 x [2 x i32]]*> [#uses=5]
+
+declare i32 @f() nounwind
+
+define i32 @main() noreturn nounwind {
+entry:
+	br label %bb1.i.outer
+
+bb1.i.outer:		; preds = %bb5.i, %entry
+	%i.0.reg2mem.0.ph.i.ph = phi i32 [ 0, %entry ], [ %4, %bb5.i ]		; <i32> [#uses=3]
+	br label %bb1.i
+
+bb1.i:		; preds = %bb3.i, %bb1.i.outer
+	%j.0.reg2mem.0.i = phi i32 [ %2, %bb3.i ], [ 0, %bb1.i.outer ]		; <i32> [#uses=3]
+	%0 = icmp eq i32 %i.0.reg2mem.0.ph.i.ph, %j.0.reg2mem.0.i		; <i1> [#uses=1]
+	br i1 %0, label %bb2.i, label %bb3.i
+
+bb2.i:		; preds = %bb1.i
+	%1 = getelementptr [2 x [2 x i32]]* @w, i32 0, i32 %i.0.reg2mem.0.ph.i.ph, i32 %j.0.reg2mem.0.i		; <i32*> [#uses=1]
+	store i32 1, i32* %1, align 4
+	br label %bb3.i
+
+bb3.i:		; preds = %bb2.i, %bb1.i
+	%2 = add i32 %j.0.reg2mem.0.i, 1		; <i32> [#uses=2]
+	%3 = icmp sgt i32 %2, 1		; <i1> [#uses=1]
+	br i1 %3, label %bb5.i, label %bb1.i
+
+bb5.i:		; preds = %bb3.i
+	%4 = add i32 %i.0.reg2mem.0.ph.i.ph, 1		; <i32> [#uses=2]
+	%5 = icmp sgt i32 %4, 1		; <i1> [#uses=1]
+	br i1 %5, label %f.exit, label %bb1.i.outer
+
+f.exit:		; preds = %bb5.i
+	%6 = load i32* getelementptr ([2 x [2 x i32]]* @w, i32 0, i32 0, i32 0), align 4		; <i32> [#uses=1]
+	%7 = icmp eq i32 %6, 1		; <i1> [#uses=1]
+	br i1 %7, label %bb, label %bb3
+
+bb:		; preds = %f.exit
+	%8 = load i32* getelementptr ([2 x [2 x i32]]* @w, i32 0, i32 1, i32 1), align 4		; <i32> [#uses=1]
+	%9 = icmp eq i32 %8, 1		; <i1> [#uses=1]
+	br i1 %9, label %bb1, label %bb3
+
+bb1:		; preds = %bb
+	%10 = load i32* getelementptr ([2 x [2 x i32]]* @w, i32 0, i32 1, i32 0), align 4		; <i32> [#uses=1]
+	%11 = icmp eq i32 %10, 0		; <i1> [#uses=1]
+	br i1 %11, label %bb2, label %bb3
+
+bb2:		; preds = %bb1
+	%12 = load i32* getelementptr ([2 x [2 x i32]]* @w, i32 0, i32 0, i32 1), align 4		; <i32> [#uses=1]
+	%13 = icmp eq i32 %12, 0		; <i1> [#uses=1]
+	br i1 %13, label %bb4, label %bb3
+
+bb3:		; preds = %bb2, %bb1, %bb, %f.exit
+	tail call void @abort() noreturn nounwind
+	unreachable
+
+bb4:		; preds = %bb2
+	ret i32 0
+}
+
+declare void @abort() noreturn nounwind
+
+declare void @exit(i32) noreturn nounwind