[llvm] 7465da2 - [ConstantRange] Introduce getMinSignedBits() method

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2020-09-22T21:37:30+03:00
New Revision: 7465da2077c2b8def7440094e15ac1199226bc25

URL: https://github.com/llvm/llvm-project/commit/7465da2077c2b8def7440094e15ac1199226bc25
DIFF: https://github.com/llvm/llvm-project/commit/7465da2077c2b8def7440094e15ac1199226bc25.diff

LOG: [ConstantRange] Introduce getMinSignedBits() method

Similar to the ConstantRange::getActiveBits(), and to similarly-named
methods in APInt, returns the bitwidth needed to represent
the given signed constant range

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/IR/ConstantRange.h b/llvm/include/llvm/IR/ConstantRange.h
index 1b7c1b92a573..20e8e67436a4 100644
--- a/llvm/include/llvm/IR/ConstantRange.h
+++ b/llvm/include/llvm/IR/ConstantRange.h
@@ -265,6 +265,10 @@ class LLVM_NODISCARD ConstantRange {
   /// in this range.
   unsigned getActiveBits() const;
 
+  /// Compute the maximal number of bits needed to represent every value
+  /// in this signed range.
+  unsigned getMinSignedBits() const;
+
   /// Subtract the specified constant from the endpoints of this constant range.
   ConstantRange subtract(const APInt &CI) const;
 

diff  --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index d2132583e8f7..4b0ad1bd25a0 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -420,6 +420,14 @@ unsigned ConstantRange::getActiveBits() const {
   return getUnsignedMax().getActiveBits();
 }
 
+unsigned ConstantRange::getMinSignedBits() const {
+  if (isEmptySet())
+    return 0;
+
+  return std::max(getSignedMin().getMinSignedBits(),
+                  getSignedMax().getMinSignedBits());
+}
+
 ConstantRange ConstantRange::subtract(const APInt &Val) const {
   assert(Val.getBitWidth() == getBitWidth() && "Wrong bit width");
   // If the set is empty or full, don't modify the endpoints.

diff  --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index 6962d349f5bc..19474eea0167 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -668,6 +668,32 @@ TEST_F(ConstantRangeTest, losslessUnsignedTruncationZeroext) {
   });
 }
 
+TEST_F(ConstantRangeTest, getMinSignedBits) {
+  unsigned Bits = 4;
+  EnumerateConstantRanges(Bits, [&](const ConstantRange &CR) {
+    unsigned Exact = 0;
+    ForeachNumInConstantRange(CR, [&](const APInt &N) {
+      Exact = std::max(Exact, N.getMinSignedBits());
+    });
+
+    unsigned ResultCR = CR.getMinSignedBits();
+    EXPECT_EQ(Exact, ResultCR);
+  });
+}
+TEST_F(ConstantRangeTest, losslessSignedTruncationSignext) {
+  unsigned Bits = 4;
+  EnumerateConstantRanges(Bits, [&](const ConstantRange &CR) {
+    unsigned MinBitWidth = CR.getMinSignedBits();
+    if (MinBitWidth == 0) {
+      EXPECT_TRUE(CR.isEmptySet());
+      return;
+    }
+    if (MinBitWidth == Bits)
+      return;
+    EXPECT_EQ(CR, CR.truncate(MinBitWidth).signExtend(Bits));
+  });
+}
+
 TEST_F(ConstantRangeTest, SubtractAPInt) {
   EXPECT_EQ(Full.subtract(APInt(16, 4)), Full);
   EXPECT_EQ(Empty.subtract(APInt(16, 4)), Empty);