[llvm] ba1e04b - [ConstantRange] Fix sdiv() with one bit values (PR56333)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-07-01T15:44:59+02:00
New Revision: ba1e04b9668b3502362f2ee36232f5f56e72b4e2

URL: https://github.com/llvm/llvm-project/commit/ba1e04b9668b3502362f2ee36232f5f56e72b4e2
DIFF: https://github.com/llvm/llvm-project/commit/ba1e04b9668b3502362f2ee36232f5f56e72b4e2.diff

LOG: [ConstantRange] Fix sdiv() with one bit values (PR56333)

Signed one bit values can only be -1 or 0, not positive. The code
was interpreting the 1 as -1 and intersecting with a full range
rather than an empty one.

Fixes https://github.com/llvm/llvm-project/issues/56333.

Added: 
    

Modified: 
    llvm/lib/IR/ConstantRange.cpp
    llvm/unittests/IR/ConstantRangeTest.cpp

Removed: 
    


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diff  --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index be6386c571b59..9d239101d8fde 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -1238,7 +1238,10 @@ ConstantRange ConstantRange::sdiv(const ConstantRange &RHS) const {
   // separately by combining division results with the appropriate signs.
   APInt Zero = APInt::getZero(getBitWidth());
   APInt SignedMin = APInt::getSignedMinValue(getBitWidth());
-  ConstantRange PosFilter(APInt(getBitWidth(), 1), SignedMin);
+  // There are no positive 1-bit values. The 1 would get interpreted as -1.
+  ConstantRange PosFilter =
+      getBitWidth() == 1 ? getEmpty()
+                         : ConstantRange(APInt(getBitWidth(), 1), SignedMin);
   ConstantRange NegFilter(SignedMin, Zero);
   ConstantRange PosL = intersectWith(PosFilter);
   ConstantRange NegL = intersectWith(NegFilter);

diff  --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index ced38a28977b2..edea097aae763 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -1259,6 +1259,9 @@ TEST_F(ConstantRangeTest, UDiv) {
 }
 
 TEST_F(ConstantRangeTest, SDiv) {
+  ConstantRange OneBit = ConstantRange::getFull(1);
+  EXPECT_EQ(OneBit.sdiv(OneBit), ConstantRange(APInt(1, 0)));
+
   unsigned Bits = 4;
   EnumerateTwoConstantRanges(Bits, [&](const ConstantRange &CR1,
                                        const ConstantRange &CR2) {