[llvm] r370389 - GlobalISel: Add maskedValueIsZero and signBitIsZero to known bits

[Matt Arsenault via llvm-commits]

Author: arsenm
Date: Thu Aug 29 10:24:36 2019
New Revision: 370389

URL: http://llvm.org/viewvc/llvm-project?rev=370389&view=rev
Log:
GlobalISel: Add maskedValueIsZero and signBitIsZero to known bits

I dropped the DemandedElts since it seems to be missing from some of
the new interfaces, but not others.

Modified:
    llvm/trunk/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
    llvm/trunk/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
    llvm/trunk/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp

Modified: llvm/trunk/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h?rev=370389&r1=370388&r2=370389&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h (original)
+++ llvm/trunk/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h Thu Aug 29 10:24:36 2019
@@ -47,6 +47,17 @@ public:
   APInt getKnownZeroes(Register R);
   APInt getKnownOnes(Register R);
 
+  /// \return true if 'V & Mask' is known to be zero in DemandedElts. We use
+  /// this predicate to simplify operations downstream.
+  /// Mask is known to be zero for bits that V cannot have.
+  bool maskedValueIsZero(Register Val, const APInt &Mask) {
+    return Mask.isSubsetOf(getKnownBits(Val).Zero);
+  }
+
+  /// \return true if the sign bit of Op is known to be zero.  We use this
+  /// predicate to simplify operations downstream.
+  bool signBitIsZero(Register Op);
+
   // FIXME: Is this the right place for G_FRAME_INDEX? Should it be in
   // TargetLowering?
   void computeKnownBitsForFrameIndex(Register R, KnownBits &Known,

Modified: llvm/trunk/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/GISelKnownBits.cpp?rev=370389&r1=370388&r2=370389&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/GlobalISel/GISelKnownBits.cpp (original)
+++ llvm/trunk/lib/CodeGen/GlobalISel/GISelKnownBits.cpp Thu Aug 29 10:24:36 2019
@@ -75,6 +75,12 @@ KnownBits GISelKnownBits::getKnownBits(R
   return Known;
 }
 
+bool GISelKnownBits::signBitIsZero(Register R) {
+  LLT Ty = MRI.getType(R);
+  unsigned BitWidth = Ty.getScalarSizeInBits();
+  return maskedValueIsZero(R, APInt::getSignMask(BitWidth));
+}
+
 APInt GISelKnownBits::getKnownZeroes(Register R) {
   return getKnownBits(R).Zero;
 }

Modified: llvm/trunk/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp?rev=370389&r1=370388&r2=370389&view=diff
==============================================================================
--- llvm/trunk/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp (original)
+++ llvm/trunk/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp Thu Aug 29 10:24:36 2019
@@ -86,3 +86,19 @@ TEST_F(GISelMITest, TestKnownBits) {
   APInt Zeroes = Info.getKnownZeroes(SrcReg);
   EXPECT_EQ(Known.Zero, Zeroes);
 }
+
+TEST_F(GISelMITest, TestSignBitIsZero) {
+  if (!TM)
+    return;
+
+  const LLT S32 = LLT::scalar(32);
+  auto SignBit = B.buildConstant(S32, 0x8000000);
+  auto Zero = B.buildConstant(S32, 0);
+
+  GISelKnownBits KnownBits(*MF);
+
+  EXPECT_TRUE(KnownBits.signBitIsZero(Zero.getReg(0)));
+  EXPECT_FALSE(KnownBits.signBitIsZero(Zero.getReg(0)));
+  EXPECT_FALSE(KnownBits.signBitIsZero(SignBit.getReg(0)));
+  EXPECT_TRUE(KnownBits.signBitIsZero(SignBit.getReg(0)));
+}