[llvm] 02295e6 - [InstCombine] matchFunnelShift - canonicalize to OR(SHL,LSHR). NFCI.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-10-12T15:10:59+01:00
New Revision: 02295e6d1a1559f0689aeca09d98f468e3f29d9a

URL: https://github.com/llvm/llvm-project/commit/02295e6d1a1559f0689aeca09d98f468e3f29d9a
DIFF: https://github.com/llvm/llvm-project/commit/02295e6d1a1559f0689aeca09d98f468e3f29d9a.diff

LOG: [InstCombine] matchFunnelShift - canonicalize to OR(SHL,LSHR). NFCI.

Simplify the shift amount matching code by canonicalizing the shift ops first.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 52b81ad2164a..06168e2424ef 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2067,13 +2067,19 @@ static Instruction *matchFunnelShift(Instruction &Or) {
 
   Value *ShVal0, *ShVal1, *ShAmt0, *ShAmt1;
   if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(ShVal0), m_Value(ShAmt0)))) ||
-      !match(Or1, m_OneUse(m_LogicalShift(m_Value(ShVal1), m_Value(ShAmt1)))))
+      !match(Or1, m_OneUse(m_LogicalShift(m_Value(ShVal1), m_Value(ShAmt1)))) ||
+      Or0->getOpcode() == Or1->getOpcode())
     return nullptr;
 
-  BinaryOperator::BinaryOps ShiftOpcode0 = Or0->getOpcode();
-  BinaryOperator::BinaryOps ShiftOpcode1 = Or1->getOpcode();
-  if (ShiftOpcode0 == ShiftOpcode1)
-    return nullptr;
+  // Canonicalize to or(shl(ShVal0, ShAmt0), lshr(ShVal1, ShAmt1)).
+  if (Or0->getOpcode() == BinaryOperator::LShr) {
+    std::swap(Or0, Or1);
+    std::swap(ShVal0, ShVal1);
+    std::swap(ShAmt0, ShAmt1);
+  }
+  assert(Or0->getOpcode() == BinaryOperator::Shl &&
+         Or1->getOpcode() == BinaryOperator::LShr &&
+         "Illegal or(shift,shift) pair");
 
   // Match the shift amount operands for a funnel shift pattern. This always
   // matches a subtraction on the R operand.
@@ -2124,16 +2130,14 @@ static Instruction *matchFunnelShift(Instruction &Or) {
   };
 
   Value *ShAmt = matchShiftAmount(ShAmt0, ShAmt1, Width);
-  bool SubIsOnLHS = false;
+  bool IsFshl = true; // Sub on LSHR.
   if (!ShAmt) {
     ShAmt = matchShiftAmount(ShAmt1, ShAmt0, Width);
-    SubIsOnLHS = true;
+    IsFshl = false; // Sub on SHL.
   }
   if (!ShAmt)
     return nullptr;
 
-  bool IsFshl = (!SubIsOnLHS && ShiftOpcode0 == BinaryOperator::Shl) ||
-                (SubIsOnLHS && ShiftOpcode1 == BinaryOperator::Shl);
   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
   Function *F = Intrinsic::getDeclaration(Or.getModule(), IID, Or.getType());
   return IntrinsicInst::Create(