[llvm] r365419 - [LoopPred] Extend LFTR normalization to the inverse EQ case

[Philip Reames via llvm-commits]

Author: reames
Date: Mon Jul  8 18:27:45 2019
New Revision: 365419

URL: http://llvm.org/viewvc/llvm-project?rev=365419&view=rev
Log:
[LoopPred] Extend LFTR normalization to the inverse EQ case

A while back, I added support for NE latches formed by LFTR.  I didn't think that quite through, as LFTR will also produce the inverse EQ form for some loops and I hadn't handled that.  This change just adds handling for that case as well.


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=365419&r1=365418&r2=365419&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp Mon Jul  8 18:27:45 2019
@@ -653,6 +653,11 @@ static void normalizePredicate(ScalarEvo
       RC.IV->getStepRecurrence(*SE)->isOne() &&
       SE->isKnownPredicate(ICmpInst::ICMP_ULE, RC.IV->getStart(), RC.Limit))
     RC.Pred = ICmpInst::ICMP_ULT;
+  if (RC.Pred == ICmpInst::ICMP_EQ &&
+      RC.IV->getStepRecurrence(*SE)->isOne() &&
+      SE->isKnownPredicate(ICmpInst::ICMP_ULE, RC.IV->getStart(), RC.Limit))
+    RC.Pred = ICmpInst::ICMP_UGE;
+
 }
 
 

Modified: llvm/trunk/test/Transforms/LoopPredication/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopPredication/basic.ll?rev=365419&r1=365418&r2=365419&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopPredication/basic.ll (original)
+++ llvm/trunk/test/Transforms/LoopPredication/basic.ll Mon Jul  8 18:27:45 2019
@@ -1756,6 +1756,49 @@ exit:
   ret i32 0
 }
 
+; Same as previous, except swapped br/cmp
+define i32 @eq_latch_dom_check_preinc(i32* %array, i32 %length, i32 %n) {
+; CHECK-LABEL: @eq_latch_dom_check_preinc(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp sle i32 [[N:%.*]], 0
+; CHECK-NEXT:    br i1 [[TMP5]], label [[EXIT:%.*]], label [[LOOP_PREHEADER:%.*]]
+; CHECK:       loop.preheader:
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[LENGTH:%.*]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ule i32 [[N]], [[TMP0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ult i32 0, [[LENGTH]]
+; CHECK-NEXT:    [[TMP3:%.*]] = and i1 [[TMP2]], [[TMP1]]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[LOOP]] ], [ 0, [[LOOP_PREHEADER]] ]
+; CHECK-NEXT:    call void (i1, ...) @llvm.experimental.guard(i1 [[TMP3]], i32 9) [ "deopt"() ]
+; CHECK-NEXT:    [[I_NEXT]] = add nuw i32 [[I]], 1
+; CHECK-NEXT:    [[DONE:%.*]] = icmp eq i32 [[I]], [[N]]
+; CHECK-NEXT:    br i1 [[DONE]], label [[EXIT_LOOPEXIT:%.*]], label [[LOOP]]
+; CHECK:       exit.loopexit:
+; CHECK-NEXT:    br label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %tmp5 = icmp sle i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+  br label %loop
+
+loop:
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %within.bounds = icmp ult i32 %i, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.next = add nuw i32 %i, 1
+  %done = icmp eq i32 %i, %n
+  br i1 %done, label %exit, label %loop
+
+exit:
+  ret i32 0
+}
+
 
 ; NE latch - can't prove (end-start) mod step == 0 (i.e. might wrap
 ; around several times or even be infinite)