[PATCH] D66923: GlobalISel: Add maskedValueIsZero and signBitIsZero to known bits

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: aditya_nandakumar, aemerson, paquette.
Herald added subscribers: Petar.Avramovic, volkan, rovka, wdng.

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


https://reviews.llvm.org/D66923

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


Index: unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
===================================================================
--- unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
+++ unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
@@ -86,3 +86,19 @@
   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)));
+}
Index: lib/CodeGen/GlobalISel/GISelKnownBits.cpp
===================================================================
--- lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -75,6 +75,12 @@
   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;
 }
Index: include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
===================================================================
--- include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
+++ include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
@@ -47,6 +47,17 @@
   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,


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