[llvm] 531f706 - GlobalISel: Implement known bits for G_MERGE_VALUES

[Matt Arsenault via llvm-commits]

Author: Matt Arsenault
Date: 2020-08-27T14:07:18-04:00
New Revision: 531f7063babc37c2bffcbbbe56219294ee407f5d

URL: https://github.com/llvm/llvm-project/commit/531f7063babc37c2bffcbbbe56219294ee407f5d
DIFF: https://github.com/llvm/llvm-project/commit/531f7063babc37c2bffcbbbe56219294ee407f5d.diff

LOG: GlobalISel: Implement known bits for G_MERGE_VALUES

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Support/KnownBits.h b/llvm/include/llvm/Support/KnownBits.h
index 69040cd23f03..4f33365c41d3 100644
--- a/llvm/include/llvm/Support/KnownBits.h
+++ b/llvm/include/llvm/Support/KnownBits.h
@@ -241,6 +241,12 @@ struct KnownBits {
   static KnownBits computeForAddSub(bool Add, bool NSW, const KnownBits &LHS,
                                     KnownBits RHS);
 
+  /// Insert the bits from a smaller known bits starting at bitPosition.
+  void insertBits(const KnownBits &SubBits, unsigned BitPosition) {
+    Zero.insertBits(SubBits.Zero, BitPosition);
+    One.insertBits(SubBits.One, BitPosition);
+  }
+
   /// Update known bits based on ANDing with RHS.
   KnownBits &operator&=(const KnownBits &RHS);
 

diff  --git a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
index e0eedc557f8f..f1928aa9edf1 100644
--- a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -387,6 +387,18 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
       Known.Zero.setBitsFrom(SrcBitWidth);
     break;
   }
+  case TargetOpcode::G_MERGE_VALUES: {
+    Register NumOps = MI.getNumOperands();
+    unsigned OpSize = MRI.getType(MI.getOperand(1).getReg()).getSizeInBits();
+
+    for (unsigned I = 0; I != NumOps - 1; ++I) {
+      KnownBits SrcOpKnown;
+      computeKnownBitsImpl(MI.getOperand(I + 1).getReg(), SrcOpKnown,
+                           DemandedElts, Depth + 1);
+      Known.insertBits(SrcOpKnown, I * OpSize);
+    }
+    break;
+  }
   }
 
   assert(!Known.hasConflict() && "Bits known to be one AND zero?");

diff  --git a/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp b/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
index e20e55c1bce4..de622129859b 100644
--- a/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/KnownBitsTest.cpp
@@ -555,3 +555,26 @@ TEST_F(AArch64GISelMITest, TestKnownBitsExt) {
   EXPECT_EQ((uint64_t)0, Res.One.getZExtValue());
   EXPECT_EQ((uint64_t)0xfffffffe, Res.Zero.getZExtValue());
 }
+
+TEST_F(AArch64GISelMITest, TestKnownBitsMergeValues) {
+  StringRef MIRString = R"(
+   %val0:_(s16) = G_CONSTANT i16 35224
+   %val1:_(s16) = G_CONSTANT i16 17494
+   %val2:_(s16) = G_CONSTANT i16 4659
+   %val3:_(s16) = G_CONSTANT i16 43981
+   %merge:_(s64) = G_MERGE_VALUES %val0, %val1, %val2, %val3
+   %mergecopy:_(s64) = COPY %merge
+)";
+  setUp(MIRString);
+  if (!TM)
+    return;
+
+  const uint64_t TestVal = UINT64_C(0xabcd123344568998);
+  Register CopyMerge = Copies[Copies.size() - 1];
+
+  GISelKnownBits Info(*MF);
+  KnownBits Res = Info.getKnownBits(CopyMerge);
+  EXPECT_EQ(64u, Res.getBitWidth());
+  EXPECT_EQ(TestVal, Res.One.getZExtValue());
+  EXPECT_EQ(~TestVal, Res.Zero.getZExtValue());
+}