[SCEV] Handle case where MaxBECount is less precise than ExactBECount for OR.

In some cases, MaxBECount can be less precise than ExactBECount for AND
and OR (the AND case was PR26207). In the OR test case, both ExactBECounts are
undef, but MaxBECount are different, so we hit the assertion below. This
patch uses the same solution the AND case already uses.

Assertion failed:
   ((isa<SCEVCouldNotCompute>(ExactNotTaken) || !isa<SCEVCouldNotCompute>(MaxNotTaken))
     && "Exact is not allowed to be less precise than Max"), function ExitLimit

This patch also consolidates test cases for both AND and OR in a single
test case.

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13245

Reviewers: sanjoy, efriedma, mkazantsev

Reviewed By: sanjoy

Differential Revision: https://reviews.llvm.org/D58853

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355259 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 290e87a1f0fb9df78f17db610e2249e65ad34ee3..f14f0463000565b3da1fd07156ae7fd371215ad8 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -7272,6 +7272,14 @@ ScalarEvolution::ExitLimit ScalarEvolution::computeExitLimitFromCondImpl(
         if (EL0.ExactNotTaken == EL1.ExactNotTaken)
           BECount = EL0.ExactNotTaken;
       }
+      // There are cases (e.g. PR26207) where computeExitLimitFromCond is able
+      // to be more aggressive when computing BECount than when computing
+      // MaxBECount.  In these cases it is possible for EL0.ExactNotTaken and
+      // EL1.ExactNotTaken to match, but for EL0.MaxNotTaken and EL1.MaxNotTaken
+      // to not.
+      if (isa<SCEVCouldNotCompute>(MaxBECount) &&
+          !isa<SCEVCouldNotCompute>(BECount))
+        MaxBECount = getConstant(getUnsignedRangeMax(BECount));
 
       return ExitLimit(BECount, MaxBECount, false,
                        {&EL0.Predicates, &EL1.Predicates});

diff --git a/test/Analysis/ScalarEvolution/exact-exit-count-more-precise.ll b/test/Analysis/ScalarEvolution/exact-exit-count-more-precise.ll
new file mode 100644 (file)
index 0000000..8b1f878
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/exact-exit-count-more-precise.ll
@@ -0,0 +1,49 @@
+; RUN: opt -analyze -scalar-evolution %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @test_and(i16 %in) {
+  br label %bb2
+
+bb2:                                              ; preds = %bb1.i, %bb2, %0
+  %_tmp44.i = icmp slt i16 %in, 2
+  br i1 %_tmp44.i, label %bb1.i, label %bb2
+
+bb1.i:                                            ; preds = %bb1.i, %bb2
+  %_tmp25.i = phi i16 [ %in, %bb2 ], [ %_tmp6.i, %bb1.i ]
+  %_tmp6.i = add nsw i16 %_tmp25.i, 1
+  %_tmp10.i = icmp sge i16 %_tmp6.i, 2
+  %exitcond.i = icmp eq i16 %_tmp6.i, 2
+  %or.cond = and i1 %_tmp10.i, %exitcond.i
+  br i1 %or.cond, label %bb2, label %bb1.i
+}
+
+; CHECK-LABEL: Determining loop execution counts for: @test_and
+; CHECK-NEXT: Loop %bb1.i: backedge-taken count is (1 + (-1 * %in))
+; CHECK-NEXT: Loop %bb1.i: max backedge-taken count is -1
+; CHECK-NEXT: Loop %bb1.i: Predicated backedge-taken count is (1 + (-1 * %in))
+
+
+define void @test_or() {
+  %C10 = icmp slt i1 undef, undef
+  br i1 %C10, label %BB, label %exit
+
+BB:                                               ; preds = %BB, %0
+  %indvars.iv = phi i64 [ -1, %BB ], [ -1, %0 ]
+  %sum.01 = phi i32 [ %2, %BB ], [ undef, %0 ]
+  %1 = trunc i64 %indvars.iv to i32
+  %2 = add nsw i32 %1, %sum.01
+  %B3 = add i32 %1, %2
+  %C11 = icmp ult i32 %2, %1
+  %C5 = icmp sle i32 %1, %B3
+  %B = or i1 %C5, %C11
+  br i1 %B, label %BB, label %exit
+
+exit:                                      ; preds = %BB, %0
+  ret void
+}
+
+; CHECK-LABEL: Determining loop execution counts for: @test_or
+; CHECK-NEXT: Loop %BB: backedge-taken count is undef
+; CHECK-NEXT: Loop %BB: max backedge-taken count is -1
+; CHECK-NEXT: Loop %BB: Predicated backedge-taken count is undef

diff --git a/test/Transforms/IndVarSimplify/pr26207.ll b/test/Transforms/IndVarSimplify/pr26207.ll
deleted file mode 100644 (file)
index 9d351e0..0000000
--- a/test/Transforms/IndVarSimplify/pr26207.ll
+++ /dev/null
@@ -1,20 +0,0 @@
-; RUN: opt -S -indvars < %s | FileCheck %s
-
-target triple = "x86_64-unknown-linux-gnu"
-
-define void @main(i16 %in) {
-; CHECK-LABEL: @main(
-  br label %bb2
-
-bb2:                                              ; preds = %bb1.i, %bb2, %0
-  %_tmp44.i = icmp slt i16 %in, 2
-  br i1 %_tmp44.i, label %bb1.i, label %bb2
-
-bb1.i:                                            ; preds = %bb1.i, %bb2
-  %_tmp25.i = phi i16 [ %in, %bb2 ], [ %_tmp6.i, %bb1.i ]
-  %_tmp6.i = add nsw i16 %_tmp25.i, 1
-  %_tmp10.i = icmp sge i16 %_tmp6.i, 2
-  %exitcond.i = icmp eq i16 %_tmp6.i, 2
-  %or.cond = and i1 %_tmp10.i, %exitcond.i
-  br i1 %or.cond, label %bb2, label %bb1.i
-}