Don't crash in SE dealing with ashr x, -1

ScalarEvolution::getSignedRange uses ComputeNumSignBits from ValueTracking on
ashr instructions. ComputeNumSignBits can return zero, but this case was not
handled correctly by the code in getSignedRange which was calling:
  APInt::getSignedMinValue(BitWidth).ashr(NS - 1)
with NS = 0, resulting in an assertion failure in APInt::ashr.

Now, we just return the conservative result (as with NS == 1).

Another bug found by llvm-stress.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185955 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 0bff21e7c3e5f24c1891feed1966ac57ae094fd7..af5051650ee2274143ad0451ff019f03dee5b8b2 100644 (file)
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3589,7 +3589,7 @@ ScalarEvolution::getSignedRange(const SCEV *S) {
     if (!U->getValue()->getType()->isIntegerTy() && !TD)
       return setSignedRange(U, ConservativeResult);
     unsigned NS = ComputeNumSignBits(U->getValue(), TD);
-    if (NS == 1)
+    if (NS <= 1)
       return setSignedRange(U, ConservativeResult);
     return setSignedRange(U, ConservativeResult.intersectWith(
       ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),

diff --git a/test/CodeGen/PowerPC/ashr-neg1.ll b/test/CodeGen/PowerPC/ashr-neg1.ll
new file mode 100644 (file)
index 0000000..28e74f4
--- /dev/null
+++ b/test/CodeGen/PowerPC/ashr-neg1.ll
@@ -0,0 +1,18 @@
+; RUN: llc -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 < %s
+target triple = "powerpc64-unknown-linux-gnu"
+
+define void @autogen_SD30723(i32) {
+BB:
+  br label %CF80
+
+CF80:                                             ; preds = %CF80, %BB
+  %B = ashr i32 %0, -1
+  br i1 undef, label %CF80, label %CF84
+
+CF84:                                             ; preds = %CF84, %CF80
+  %Cmp62 = icmp sge i32 undef, %B
+  br i1 %Cmp62, label %CF84, label %CF85
+
+CF85:                                             ; preds = %CF85, %CF84
+  br label %CF85
+}