[llvm] r362727 - [LoopPred] Fix a bug in unconditional latch bailout introduced in r362284

[Philip Reames via llvm-commits]

Author: reames
Date: Thu Jun  6 11:02:36 2019
New Revision: 362727

URL: http://llvm.org/viewvc/llvm-project?rev=362727&view=rev
Log:
[LoopPred] Fix a bug in unconditional latch bailout introduced in r362284

This is a really silly bug that even a simple test w/an unconditional latch would have caught.  I tried to guard against the case, but put it in the wrong if check.  Oops.


Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp
    llvm/trunk/test/Transforms/LoopPredication/basic.ll

Modified: llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp?rev=362727&r1=362726&r2=362727&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp Thu Jun  6 11:02:36 2019
@@ -850,7 +850,7 @@ Optional<LoopICmp> LoopPredication::pars
   }
 
   auto *BI = dyn_cast<BranchInst>(LoopLatch->getTerminator());
-  if (!BI) {
+  if (!BI || !BI->isConditional()) {
     LLVM_DEBUG(dbgs() << "Failed to match the latch terminator!\n");
     return None;
   }
@@ -860,7 +860,7 @@ Optional<LoopICmp> LoopPredication::pars
       "One of the latch's destinations must be the header");
 
   auto *ICI = dyn_cast<ICmpInst>(BI->getCondition());
-  if (!ICI || !BI->isConditional()) {
+  if (!ICI) {
     LLVM_DEBUG(dbgs() << "Failed to match the latch condition!\n");
     return None;
   }

Modified: llvm/trunk/test/Transforms/LoopPredication/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopPredication/basic.ll?rev=362727&r1=362726&r2=362727&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopPredication/basic.ll (original)
+++ llvm/trunk/test/Transforms/LoopPredication/basic.ll Thu Jun  6 11:02:36 2019
@@ -1853,3 +1853,29 @@ exit:
   ret i32 0
 }
 
+; Negative test, make sure we don't crash on unconditional latches
+; TODO: there's no reason we shouldn't be able to predicate the
+; condition for an statically infinite loop.
+define i32 @unconditional_latch(i32* %a, i32 %length) {
+; CHECK-LABEL: @unconditional_latch(
+; CHECK-NEXT:  loop.preheader:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[LOOP]] ], [ 400, [[LOOP_PREHEADER:%.*]] ]
+; CHECK-NEXT:    [[WITHIN_BOUNDS:%.*]] = icmp ult i32 [[I]], [[LENGTH:%.*]]
+; CHECK-NEXT:    call void (i1, ...) @llvm.experimental.guard(i1 [[WITHIN_BOUNDS]], i32 9) [ "deopt"() ]
+; CHECK-NEXT:    store volatile i32 0, i32* [[A:%.*]]
+; CHECK-NEXT:    [[I_NEXT]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label [[LOOP]]
+;
+loop.preheader:
+  br label %loop
+
+loop:
+  %i = phi i32 [ %i.next, %loop ], [ 400, %loop.preheader ]
+  %within.bounds = icmp ult i32 %i, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  store volatile i32 0, i32* %a
+  %i.next = add i32 %i, 1
+  br label %loop
+}