[PATCH] D55140: [ValueTracking] Support funnel shifts in computeKnownBits()

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
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This is a continuation of D54869 <https://reviews.llvm.org/D54869>, this time adding support for funnel shifts in ValueTracking computeKnownBits(). Implementation is essentially the same as for InstCombineSimplifyDemandedBits.


Repository:
  rL LLVM

https://reviews.llvm.org/D55140

Files:
  lib/Analysis/ValueTracking.cpp
  unittests/Analysis/ValueTrackingTest.cpp


Index: unittests/Analysis/ValueTrackingTest.cpp
===================================================================
--- unittests/Analysis/ValueTrackingTest.cpp
+++ unittests/Analysis/ValueTrackingTest.cpp
@@ -577,3 +577,51 @@
       "}\n");
   expectKnownBits(/*zero*/ 95u, /*one*/ 32u);
 }
+
+TEST_F(ComputeKnownBitsTest, ComputeKnownFshl) {
+  // fshl(....1111....0000, 00..1111........, 6)
+  // = 11....000000..11
+  parseAssembly(
+      "define i16 @test(i16 %a, i16 %b) {\n"
+      "  %aa = shl i16 %a, 4\n"
+      "  %bb = lshr i16 %b, 2\n"
+      "  %aaa = or i16 %aa, 3840\n"
+      "  %bbb = or i16 %bb, 3840\n"
+      "  %A = call i16 @llvm.fshl.i16(i16 %aaa, i16 %bbb, i16 6)\n"
+      "  ret i16 %A\n"
+      "}\n"
+      "declare i16 @llvm.fshl.i16(i16, i16, i16)\n");
+  expectKnownBits(/*zero*/ 1008u, /*one*/ 49155u);
+}
+
+TEST_F(ComputeKnownBitsTest, ComputeKnownFshr) {
+  // fshr(....1111....0000, 00..1111........, 26)
+  // = 11....000000..11
+  parseAssembly(
+      "define i16 @test(i16 %a, i16 %b) {\n"
+      "  %aa = shl i16 %a, 4\n"
+      "  %bb = lshr i16 %b, 2\n"
+      "  %aaa = or i16 %aa, 3840\n"
+      "  %bbb = or i16 %bb, 3840\n"
+      "  %A = call i16 @llvm.fshr.i16(i16 %aaa, i16 %bbb, i16 26)\n"
+      "  ret i16 %A\n"
+      "}\n"
+      "declare i16 @llvm.fshr.i16(i16, i16, i16)\n");
+  expectKnownBits(/*zero*/ 1008u, /*one*/ 49155u);
+}
+
+TEST_F(ComputeKnownBitsTest, ComputeKnownFshlZero) {
+  // fshl(....1111....0000, 00..1111........, 0)
+  // = ....1111....0000
+  parseAssembly(
+      "define i16 @test(i16 %a, i16 %b) {\n"
+      "  %aa = shl i16 %a, 4\n"
+      "  %bb = lshr i16 %b, 2\n"
+      "  %aaa = or i16 %aa, 3840\n"
+      "  %bbb = or i16 %bb, 3840\n"
+      "  %A = call i16 @llvm.fshl.i16(i16 %aaa, i16 %bbb, i16 0)\n"
+      "  ret i16 %A\n"
+      "}\n"
+      "declare i16 @llvm.fshl.i16(i16, i16, i16)\n");
+  expectKnownBits(/*zero*/ 15u, /*one*/ 3840u);
+}
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1506,6 +1506,27 @@
         // of bits which might be set provided by popcnt KnownOne2.
         break;
       }
+      case Intrinsic::fshr:
+      case Intrinsic::fshl: {
+        const APInt *SA;
+        if (!match(I->getOperand(2), m_APInt(SA)))
+          break;
+
+        // Normalize to funnel shift left.
+        uint64_t ShiftAmt = SA->urem(BitWidth);
+        if (II->getIntrinsicID() == Intrinsic::fshr)
+          ShiftAmt = BitWidth - ShiftAmt;
+
+        KnownBits Known3(Known);
+        computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
+        computeKnownBits(I->getOperand(1), Known3, Depth + 1, Q);
+
+        Known.Zero =
+            Known2.Zero.shl(ShiftAmt) | Known3.Zero.lshr(BitWidth - ShiftAmt);
+        Known.One =
+            Known2.One.shl(ShiftAmt) | Known3.One.lshr(BitWidth - ShiftAmt);
+        break;
+      }
       case Intrinsic::x86_sse42_crc32_64_64:
         Known.Zero.setBitsFrom(32);
         break;


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