Commit 5746c76f authored by Philip Reames's avatar Philip Reames
Browse files

Revert "[IndVars] Break backedge and replace PHIs if loop exits on 1st iteration" 

This reverts commit d9ca4448.  See review for why.
parent 1a56a291

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

+0 −8
Original line number Diff line number Diff line
@@ -1465,15 +1465,8 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) { 


  bool Changed = false;

  bool SkipLastIter = false;

  bool ExitsOnFirstIter = false;

  SmallSet<const SCEV*, 8> DominatingExitCounts;

  for (BasicBlock *ExitingBB : ExitingBlocks) {

    if (ExitsOnFirstIter) {

      // If proved that some earlier exit is taken

      // on 1st iteration, then fold this one.

      foldExit(L, ExitingBB, true, DeadInsts);

      continue;

    }

    const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);

    if (isa<SCEVCouldNotCompute>(ExitCount)) {

      // Okay, we do not know the exit count here. Can we at least prove that it
@@ -1523,7 +1516,6 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) { 
      foldExit(L, ExitingBB, true, DeadInsts);

      replaceLoopPHINodesWithPreheaderValues(L, DeadInsts);

      Changed = true;

      ExitsOnFirstIter = true;

      continue;

    }

llvm/test/Transforms/IndVarSimplify/eliminate-backedge.ll

+5 −2
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ define i1 @kill_backedge_and_phis(i8* align 1 %lhs, i8* align 1 %rhs, i32 %len) 
; CHECK:       loop_preheader:

; CHECK-NEXT:    br label %loop

; CHECK:       loop:

; CHECK-NEXT:    %iv.next = add nuw nsw i32 0, 1

; CHECK-NEXT:    %left_ptr = getelementptr inbounds i8, i8* %lhs, i32 0

; CHECK-NEXT:    %right_ptr = getelementptr inbounds i8, i8* %rhs, i32 0

; CHECK-NEXT:    %result = call i1 @foo(i8* %left_ptr, i8* %right_ptr)
@@ -24,10 +25,12 @@ define i1 @kill_backedge_and_phis(i8* align 1 %lhs, i8* align 1 %rhs, i32 %len) 
; CHECK-NEXT:    br i1 false, label %exiting_2, label %exit.loopexit

; CHECK:       exiting_2:

; CHECK-NEXT:    %bar_ret = call i1 @bar()

; CHECK-NEXT:    br i1 true, label %exit.loopexit, label %exiting_3

; CHECK-NEXT:    br i1 %bar_ret, label %exit.loopexit, label %exiting_3

; CHECK:       exiting_3:

; CHECK-NEXT:    %baz_ret = call i1 @baz()

; CHECK-NEXT:    br i1 false, label %loop, label %exit.loopexit

; CHECK-NEXT:    %continue = icmp ne i32 %iv.next, %len

; CHECK-NEXT:    %or.cond = select i1 %baz_ret, i1 %continue, i1 false

; CHECK-NEXT:    br i1 %or.cond, label %loop, label %exit.loopexit

; CHECK:       exit.loopexit:

; CHECK-NEXT:    %val.ph = phi i1 [ %baz_ret, %exiting_3 ], [ %bar_ret, %exiting_2 ], [ %iv.wide.is_not_zero, %exiting_1 ], [ %result, %loop ]

; CHECK-NEXT:    br label %exit