This reverts commit r306272.

Revert "[MBP] do not rotate loop if it creates extra branch"

It breaks the sanitizer build bots. Need to fix this.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306276 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineBlockPlacement.cpp

@@ -1944,35 +1944,6 @@ void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain,
   if (ExitIt == LoopChain.end())
     return;
 
-  // Rotating a loop exit to the bottom when there is a fallthrough to top
-  // trades the entry fallthrough for an exit fallthrough.
-  // If there is no bottom->top edge, but the chosen exit block does have
-  // a fallthrough, we break that fallthrough for nothing in return.
-
-  // Let's consider an example. We have a built chain of basic blocks
-  // B1, B2, ..., Bn, where Bk is a ExitingBB - chosen exit block.
-  // By doing a rotation we get
-  // Bk+1, ..., Bn, B1, ..., Bk
-  // Break of fallthrough to B1 is compensated by a fallthrough from Bk.
-  // If we had a fallthrough Bk -> Bk+1 it is broken now.
-  // It might be compensated by fallthrough Bn -> B1.
-  // So we have a condition to avoid creation of extra branch by loop rotation.
-  // All below must be true to avoid loop rotation:
-  //   If there is a fallthrough to top (B1)
-  //   There was fallthrough from chosen exit block (Bk) to next one (Bk+1)
-  //   There is no fallthrough from bottom (Bn) to top (B1).
-  // Please note that there is no exit fallthrough from Bn because we checked it
-  // above.
-  if (ViableTopFallthrough) {
-    MachineBasicBlock *NextBlockInChain = *std::next(ExitIt);
-    MachineBasicBlock *Bottom = *std::prev(LoopChain.end());
-    if (NextBlockInChain->isPredecessor(ExitingBB))
-      if (!Top->isPredecessor(Bottom))
-        return;
-  }
-
-  DEBUG(dbgs() << "Rotating loop to put exit " << getBlockName(ExitingBB)
-               << " at bottom\n");
   std::rotate(LoopChain.begin(), std::next(ExitIt), LoopChain.end());
 }
 

test/CodeGen/X86/block-placement.ll

@@ -354,7 +354,6 @@ define void @unnatural_cfg2() {
 ; single-source GCC.
 ; CHECK-LABEL: unnatural_cfg2
 ; CHECK: %entry
-; CHECK: %loop.header
 ; CHECK: %loop.body1
 ; CHECK: %loop.body2
 ; CHECK: %loop.body4
@@ -362,6 +361,7 @@ define void @unnatural_cfg2() {
 ; CHECK: %loop.inner2.begin
 ; CHECK: %loop.body3
 ; CHECK: %loop.inner1.begin
+; CHECK: %loop.header
 ; CHECK: %bail
 
 entry:
@@ -1491,54 +1491,6 @@ ret:                                              ; preds = %endif, %then
   ret void
 }
 
-define i32 @not_rotate_if_extra_branch(i32 %count) {
-; Test checks that there is no loop rotation
-; if it introduces extra branch.
-; Specifically in this case because best exit is .header
-; but it has fallthrough to .middle block and last block in
-; loop chain .slow does not have afallthrough to .header.
-; CHECK-LABEL: not_rotate_if_extra_branch
-; CHECK: %.entry
-; CHECK: %.header
-; CHECK: %.middle
-; CHECK: %.backedge
-; CHECK: %.slow
-; CHECK: %.bailout
-; CHECK: %.stop
-.entry:
-  %sum.0 = shl nsw i32 %count, 1
-  br label %.header
-
-.header:
-  %i = phi i32 [ %i.1, %.backedge ], [ 0, %.entry ]
-  %sum = phi i32 [ %sum.1, %.backedge ], [ %sum.0, %.entry ]
-  %is_exc = icmp sgt i32 %i, 9000000
-  br i1 %is_exc, label %.bailout, label %.middle, !prof !13
-
-.bailout:
-  %sum.2 = add nsw i32 %count, 1
-  br label %.stop
-
-.middle:
-  %pr.1 = and i32 %i, 1023
-  %pr.2 = icmp eq i32 %pr.1, 0
-  br i1 %pr.2, label %.slow, label %.backedge, !prof !14
-
-.slow:
-  tail call void @effect(i32 %sum)
-  br label %.backedge
-
-.backedge:
-  %sum.1 = add nsw i32 %i, %sum
-  %i.1 = add nsw i32 %i, 1
-  %end = icmp slt i32 %i.1, %count
-  br i1 %end, label %.header, label %.stop, !prof !15
-
-.stop:
-  %sum.phi = phi i32 [ %sum.1, %.backedge ], [ %sum.2, %.bailout ]
-  ret i32 %sum.phi
-}
-
 declare void @effect(i32)
 
 !5 = !{!"branch_weights", i32 84, i32 16}
@@ -1549,6 +1501,3 @@ declare void @effect(i32)
 !10 = !{!"branch_weights", i32 90, i32 10}
 !11 = !{!"branch_weights", i32 1, i32 1}
 !12 = !{!"branch_weights", i32 5, i32 3}
-!13 = !{!"branch_weights", i32 1, i32 1}
-!14 = !{!"branch_weights", i32 1, i32 1023}
-!15 = !{!"branch_weights", i32 4095, i32 1}

test/CodeGen/X86/code_placement_cold_loop_blocks.ll

@@ -37,7 +37,7 @@ end:
   ret void
 }
 
-define void @nested_loop_0(i1 %flag) !prof !1 {
+define void @nested_loop_0() !prof !1 {
 ; Test if a block that is cold in the inner loop but not cold in the outer loop
 ; will merged to the outer loop chain.
 ;
@@ -68,7 +68,8 @@ if.then:
 
 if.else:
   call void @e()
-  br i1 %flag, label %header2, label %header, !prof !3
+  %call2 = call zeroext i1 @a()
+  br i1 %call2, label %header2, label %header, !prof !3
 
 end:
   call void @f()