[ConstantRange] Fix off by 1 bugs in UIToFP and SIToFP handling. (#86041

)

We were passing the min and max values of the range to the ConstantRange
constructor, but the constructor expects the upper bound to 1 more than
the max value so we need to add 1.

We also need to use getNonEmpty so that passing 0, 0 to the constructor
creates a full range rather than an empty range. And passing smin,
smax+1 doesn't cause an assertion.

I believe this fixes at least some of the reason #79158 was reverted.

llvm/lib/IR/ConstantRange.cpp

@@ -746,7 +746,7 @@ ConstantRange ConstantRange::castOp(Instruction::CastOps CastOp,
       Min = Min.zext(ResultBitWidth);
       Max = Max.zext(ResultBitWidth);
     }
-    return ConstantRange(std::move(Min), std::move(Max));
+    return getNonEmpty(std::move(Min), std::move(Max) + 1);
   }
   case Instruction::SIToFP: {
     // TODO: use input range if available
@@ -757,7 +757,7 @@ ConstantRange ConstantRange::castOp(Instruction::CastOps CastOp,
       SMin = SMin.sext(ResultBitWidth);
       SMax = SMax.sext(ResultBitWidth);
     }
-    return ConstantRange(std::move(SMin), std::move(SMax));
+    return getNonEmpty(std::move(SMin), std::move(SMax) + 1);
   }
   case Instruction::FPTrunc:
   case Instruction::FPExt:

llvm/test/Transforms/Float2Int/pr79158.ll

@@ -6,9 +6,10 @@ define i32 @pr79158(i32 %x) {
 ; CHECK-SAME: i32 [[X:%.*]]) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[X]], 0
-; CHECK-NEXT:    [[TMP0:%.*]] = zext i1 [[CMP]] to i32
-; CHECK-NEXT:    [[MUL1:%.*]] = mul i32 [[TMP0]], 2147483647
-; CHECK-NEXT:    ret i32 [[MUL1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = zext i1 [[CMP]] to i64
+; CHECK-NEXT:    [[MUL1:%.*]] = mul i64 [[TMP0]], 4294967295
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[MUL1]] to i32
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
 entry:
   %cmp = icmp sgt i32 %x, 0

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -2479,6 +2479,24 @@ TEST_F(ConstantRangeTest, castOps) {
   ConstantRange IntToPtr = A.castOp(Instruction::IntToPtr, 64);
   EXPECT_EQ(64u, IntToPtr.getBitWidth());
   EXPECT_TRUE(IntToPtr.isFullSet());
+
+  ConstantRange UIToFP = A.castOp(Instruction::UIToFP, 16);
+  EXPECT_EQ(16u, UIToFP.getBitWidth());
+  EXPECT_TRUE(UIToFP.isFullSet());
+
+  ConstantRange UIToFP2 = A.castOp(Instruction::UIToFP, 64);
+  ConstantRange B(APInt(64, 0), APInt(64, 65536));
+  EXPECT_EQ(64u, UIToFP2.getBitWidth());
+  EXPECT_EQ(B, UIToFP2);
+
+  ConstantRange SIToFP = A.castOp(Instruction::SIToFP, 16);
+  EXPECT_EQ(16u, SIToFP.getBitWidth());
+  EXPECT_TRUE(SIToFP.isFullSet());
+
+  ConstantRange SIToFP2 = A.castOp(Instruction::SIToFP, 64);
+  ConstantRange C(APInt(64, -32768), APInt(64, 32768));
+  EXPECT_EQ(64u, SIToFP2.getBitWidth());
+  EXPECT_EQ(C, SIToFP2);
 }
 
 TEST_F(ConstantRangeTest, binaryAnd) {