From b2b9a2375848d37f6104ce01bd34bf2a3ddc9d2e Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault@amd.com>
Date: Thu, 29 Aug 2019 17:24:36 +0000
Subject: [PATCH] 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.

llvm-svn: 370389
---
 .../llvm/CodeGen/GlobalISel/GISelKnownBits.h     | 11 +++++++++++
 llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp   |  6 ++++++
 .../CodeGen/GlobalISel/KnownBitsTest.cpp         | 16 ++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/llvm/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h b/llvm/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
index f7b804b3a21169..e2a088f9217644 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h
@@ -47,6 +47,17 @@ class GISelKnownBits : public GISelChangeObserver {
   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,
diff --git a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
index 31e28f5ed5c64d..0870aa3812fe9b 100644
--- a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -75,6 +75,12 @@ KnownBits GISelKnownBits::getKnownBits(Register 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;
 }
diff --git a/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp b/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
index f67184fc2081d7..42d676f4a00e59 100644
--- a/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
@@ -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)));
+}