[llvm-branch-commits] [llvm] 6895581 - [Support] Add KnownBits::getSignedMinValue/getSignedMaxValue helpers.

[Simon Pilgrim via llvm-branch-commits]

Author: Simon Pilgrim
Date: 2020-12-24T14:10:12Z
New Revision: 6895581fd2c1cbe1a51d157d40219b7bb51a9cd5

URL: https://github.com/llvm/llvm-project/commit/6895581fd2c1cbe1a51d157d40219b7bb51a9cd5
DIFF: https://github.com/llvm/llvm-project/commit/6895581fd2c1cbe1a51d157d40219b7bb51a9cd5.diff

LOG: [Support] Add KnownBits::getSignedMinValue/getSignedMaxValue helpers.

Add unit test coverage - a followup will update InstCombineCompares.cpp to use this and could be used by D86578 as well.

Added: 
    

Modified: 
    llvm/include/llvm/Support/KnownBits.h
    llvm/unittests/Support/KnownBitsTest.cpp

Removed: 
    


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diff  --git a/llvm/include/llvm/Support/KnownBits.h b/llvm/include/llvm/Support/KnownBits.h
index 2acaecfc3440..ec88b9807174 100644
--- a/llvm/include/llvm/Support/KnownBits.h
+++ b/llvm/include/llvm/Support/KnownBits.h
@@ -119,12 +119,32 @@ struct KnownBits {
     return One;
   }
 
+  /// Return the minimal signed value possible given these KnownBits.
+  APInt getSignedMinValue() const {
+    // Assume that all bits that aren't known-ones are zeros.
+    APInt Min = One;
+    // Sign bit is unknown.
+    if (Zero.isSignBitClear() && One.isSignBitClear())
+      Min.setSignBit();
+    return Min;
+  }
+
   /// Return the maximal unsigned value possible given these KnownBits.
   APInt getMaxValue() const {
     // Assume that all bits that aren't known-zeros are ones.
     return ~Zero;
   }
 
+  /// Return the maximal signed value possible given these KnownBits.
+  APInt getSignedMaxValue() const {
+    // Assume that all bits that aren't known-zeros are ones.
+    APInt Max = ~Zero;
+    // Sign bit is unknown.
+    if (Zero.isSignBitClear() && One.isSignBitClear())
+      Max.clearSignBit();
+    return Max;
+  }
+
   /// Return known bits for a truncation of the value we're tracking.
   KnownBits trunc(unsigned BitWidth) const {
     return KnownBits(Zero.trunc(BitWidth), One.trunc(BitWidth));

diff  --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
index c5eb96efc85e..528a645ec51a 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -295,6 +295,20 @@ TEST(KnownBitsTest, GetMinMaxVal) {
   });
 }
 
+TEST(KnownBitsTest, GetSignedMinMaxVal) {
+  unsigned Bits = 4;
+  ForeachKnownBits(Bits, [&](const KnownBits &Known) {
+    APInt Min = APInt::getSignedMaxValue(Bits);
+    APInt Max = APInt::getSignedMinValue(Bits);
+    ForeachNumInKnownBits(Known, [&](const APInt &N) {
+      Min = APIntOps::smin(Min, N);
+      Max = APIntOps::smax(Max, N);
+    });
+    EXPECT_EQ(Min, Known.getSignedMinValue());
+    EXPECT_EQ(Max, Known.getSignedMaxValue());
+  });
+}
+
 TEST(KnownBitsTest, SExtOrTrunc) {
   const unsigned NarrowerSize = 4;
   const unsigned BaseSize = 6;