[ConstantRange] Infer nonnegative for mul nuw nsw (#100554)

Alive2: https://alive2.llvm.org/ce/z/byzmsV

Author: dtcxzyw

llvm/lib/IR/ConstantRange.cpp

@@ -1242,6 +1242,17 @@ ConstantRange::multiplyWithNoWrap(const ConstantRange &Other,
   if (NoWrapKind & OverflowingBinaryOperator::NoUnsignedWrap)
     Result = Result.intersectWith(umul_sat(Other), RangeType);
 
+  // mul nsw nuw X, Y s>= 0 if X s> 1 or Y s> 1
+  if ((NoWrapKind == (OverflowingBinaryOperator::NoSignedWrap |
+                      OverflowingBinaryOperator::NoUnsignedWrap)) &&
+      !Result.isAllNonNegative()) {
+    if (getSignedMin().sgt(1) || Other.getSignedMin().sgt(1))
+      Result = Result.intersectWith(
+          getNonEmpty(APInt::getZero(getBitWidth()),
+                      APInt::getSignedMinValue(getBitWidth())),
+          RangeType);
+  }
+
   return Result;
 }
 

llvm/test/Transforms/CorrelatedValuePropagation/mul.ll

@@ -224,3 +224,35 @@ define i1 @one_bit(i1 %a, i1 %b) {
   %mul = mul i1 %a, %b
   ret i1 %mul
 }
+
+define i1 @test_mul_nuw_nsw_nneg(i32 %x, i32 range(i32 3, 2147483648) %y) {
+; CHECK-LABEL: @test_mul_nuw_nsw_nneg(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MUL:%.*]] = mul nuw nsw i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    ret i1 true
+;
+entry:
+  %mul = mul nuw nsw i32 %x, %y
+  %cmp = icmp sgt i32 %mul, -1
+  ret i1 %cmp
+}
+
+define i1 @test_mul_nuw_nsw_nneg_complex(i32 %x, i32 noundef %y, i32 %z) {
+; CHECK-LABEL: @test_mul_nuw_nsw_nneg_complex(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp sgt i32 [[Y:%.*]], 2
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 [[X:%.*]], 0
+; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[CMP2]], i32 3, i32 4
+; CHECK-NEXT:    [[SEL2:%.*]] = select i1 [[CMP1]], i32 [[Y]], i32 [[SEL1]]
+; CHECK-NEXT:    [[MUL:%.*]] = mul nuw nsw i32 [[X]], [[SEL2]]
+; CHECK-NEXT:    ret i1 true
+;
+entry:
+  %cmp1 = icmp sgt i32 %y, 2
+  %cmp2 = icmp eq i32 %x, 0
+  %sel1 = select i1 %cmp2, i32 3, i32 4
+  %sel2 = select i1 %cmp1, i32 %y, i32 %sel1
+  %mul = mul nuw nsw i32 %x, %sel2
+  %cmp3 = icmp sgt i32 %mul, -1
+  ret i1 %cmp3
+}

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -1070,6 +1070,24 @@ TEST_F(ConstantRangeTest, MultiplyWithNoWrap) {
                 .multiplyWithNoWrap(ConstantRange(APInt(8, 100), APInt(8, 121)),
                                     OBO::NoSignedWrap),
             ConstantRange::getEmpty(8));
+  EXPECT_TRUE(ConstantRange::getFull(8)
+                  .multiplyWithNoWrap(ConstantRange(APInt(8, 2), APInt(8, 128)),
+                                      OBO::NoUnsignedWrap | OBO::NoSignedWrap)
+                  .isAllNonNegative());
+  EXPECT_TRUE(ConstantRange(APInt(8, 2), APInt(8, 128))
+                  .multiplyWithNoWrap(ConstantRange::getFull(8),
+                                      OBO::NoUnsignedWrap | OBO::NoSignedWrap)
+                  .isAllNonNegative());
+  EXPECT_FALSE(
+      ConstantRange::getFull(8)
+          .multiplyWithNoWrap(ConstantRange(APInt(8, 1), APInt(8, 128)),
+                              OBO::NoUnsignedWrap | OBO::NoSignedWrap)
+          .isAllNonNegative());
+  EXPECT_FALSE(
+      ConstantRange::getFull(8)
+          .multiplyWithNoWrap(ConstantRange(APInt(8, 2), APInt(8, 128)),
+                              OBO::NoSignedWrap)
+          .isAllNonNegative());
 
   TestBinaryOpExhaustive(
       [](const ConstantRange &CR1, const ConstantRange &CR2) {