diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp index 99647bf86073c..aa15b605a33ff 100644 --- a/llvm/lib/Analysis/ScalarEvolution.cpp +++ b/llvm/lib/Analysis/ScalarEvolution.cpp @@ -11653,30 +11653,6 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS, if (PredicatedIV || !NoWrap || isKnownNonPositive(Stride) || !loopIsFiniteByAssumption(L)) return getCouldNotCompute(); - - // We allow a potentially zero stride, but we need to divide by stride - // below. Since the loop can't be infinite and this check must control - // the sole exit, we can infer the exit must be taken on the first - // iteration (e.g. backedge count = 0) if the stride is zero. Given that, - // we know the numerator in the divides below must be zero, so we can - // pick an arbitrary non-zero value for the denominator (e.g. stride) - // and produce the right result. - // FIXME: Handle the case where Stride is poison? - auto wouldZeroStrideBeUB = [&]() { - // Proof by contradiction. Suppose the stride were zero. If we can - // prove that the backedge *is* taken on the first iteration, then since - // we know this condition controls the sole exit, we must have an - // infinite loop. We can't have a (well defined) infinite loop per - // check just above. - // Note: The (Start - Stride) term is used to get the start' term from - // (start' + stride,+,stride). Remember that we only care about the - // result of this expression when stride == 0 at runtime. - auto *StartIfZero = getMinusSCEV(IV->getStart(), Stride); - return isLoopEntryGuardedByCond(L, Cond, StartIfZero, RHS); - }; - if (!isKnownNonZero(Stride) && !wouldZeroStrideBeUB()) { - Stride = getUMaxExpr(Stride, getOne(Stride->getType())); - } } else if (!Stride->isOne() && !NoWrap) { auto isUBOnWrap = [&]() { // Can we prove this loop *must* be UB if overflow of IV occurs? diff --git a/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll b/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll index 1af81a3ddaa64..97399d7acb563 100644 --- a/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll +++ b/llvm/test/Analysis/ScalarEvolution/trip-count-unknown-stride.ll @@ -34,8 +34,8 @@ for.end: ; preds = %for.body, %entry ; Check that we are able to compute trip count of a loop without an entry guard. -; CHECK: Determining loop execution counts for: @foo2 -; CHECK: backedge-taken count is ((-1 + (-1 * %s) + (1 umax %s) + (%n smax %s)) /u (1 umax %s)) +; CHECK-LABEL: Determining loop execution counts for: @foo2 +; CHECK: backedge-taken count is ((-1 + (%n smax %s)) /u %s) ; We should have a conservative estimate for the max backedge taken count for ; loops with unknown stride. @@ -84,8 +84,8 @@ for.end: ; preds = %for.body, %entry } ; Same as foo2, but with mustprogress on loop, not function -; CHECK: Determining loop execution counts for: @foo4 -; CHECK: backedge-taken count is ((-1 + (-1 * %s) + (1 umax %s) + (%n smax %s)) /u (1 umax %s)) +; CHECK-LABEL: Determining loop execution counts for: @foo4 +; CHECK: backedge-taken count is ((-1 + (%n smax %s)) /u %s) ; CHECK: max backedge-taken count is -1 define void @foo4(i32* nocapture %A, i32 %n, i32 %s) { @@ -108,7 +108,7 @@ for.end: ; preds = %for.body, %entry ; A more complex case with pre-increment compare instead of post-increment. ; CHECK-LABEL: Determining loop execution counts for: @foo5 -; CHECK: Loop %for.body: backedge-taken count is ((-1 + (-1 * %start) + (1 umax %s) + (%n smax %start)) /u (1 umax %s)) +; CHECK: Loop %for.body: backedge-taken count is ((-1 + (-1 * %start) + (%n smax %start) + %s) /u %s) ; We should have a conservative estimate for the max backedge taken count for ; loops with unknown stride.