[llvm] 89657b3 - [InstCombine] narrowRotate - canonicalize to OR(SHL,LSHR). NFCI.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-10-14T16:45:00+01:00
New Revision: 89657b3a3b5772558ac084dc03591de5dab3f1f1

URL: https://github.com/llvm/llvm-project/commit/89657b3a3b5772558ac084dc03591de5dab3f1f1
DIFF: https://github.com/llvm/llvm-project/commit/89657b3a3b5772558ac084dc03591de5dab3f1f1.diff

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

Match the canonicalization code that was added to matchFunnelShift at rG02295e6d1a15

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 478032f56bdf..d8eddb69de87 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -531,19 +531,25 @@ Instruction *InstCombinerImpl::narrowRotate(TruncInst &Trunc) {
 
   // First, find an or'd pair of opposite shifts with the same shifted operand:
   // trunc (or (lshr ShVal, ShAmt0), (shl ShVal, ShAmt1))
-  Value *Or0, *Or1;
-  if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
+  BinaryOperator *Or0, *Or1;
+  if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
     return nullptr;
 
   Value *ShVal, *ShAmt0, *ShAmt1;
   if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(ShVal), m_Value(ShAmt0)))) ||
-      !match(Or1, m_OneUse(m_LogicalShift(m_Specific(ShVal), m_Value(ShAmt1)))))
+      !match(Or1,
+             m_OneUse(m_LogicalShift(m_Specific(ShVal), m_Value(ShAmt1)))) ||
+      Or0->getOpcode() == Or1->getOpcode())
     return nullptr;
 
-  auto ShiftOpcode0 = cast<BinaryOperator>(Or0)->getOpcode();
-  auto ShiftOpcode1 = cast<BinaryOperator>(Or1)->getOpcode();
-  if (ShiftOpcode0 == ShiftOpcode1)
-    return nullptr;
+  // Canonicalize to or(shl(ShVal, ShAmt0), lshr(ShVal, ShAmt1)).
+  if (Or0->getOpcode() == BinaryOperator::LShr) {
+    std::swap(Or0, Or1);
+    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 rotate pattern. This always matches
   // a subtraction on the R operand.
@@ -570,10 +576,10 @@ Instruction *InstCombinerImpl::narrowRotate(TruncInst &Trunc) {
   };
 
   Value *ShAmt = matchShiftAmount(ShAmt0, ShAmt1, NarrowWidth);
-  bool SubIsOnLHS = false;
+  bool IsFshl = true; // Sub on LSHR.
   if (!ShAmt) {
     ShAmt = matchShiftAmount(ShAmt1, ShAmt0, NarrowWidth);
-    SubIsOnLHS = true;
+    IsFshl = false; // Sub on SHL.
   }
   if (!ShAmt)
     return nullptr;
@@ -591,8 +597,6 @@ Instruction *InstCombinerImpl::narrowRotate(TruncInst &Trunc) {
   // llvm.fshl.i8(trunc(ShVal), trunc(ShVal), trunc(ShAmt))
   Value *NarrowShAmt = Builder.CreateTrunc(ShAmt, DestTy);
   Value *X = Builder.CreateTrunc(ShVal, DestTy);
-  bool IsFshl = (!SubIsOnLHS && ShiftOpcode0 == BinaryOperator::Shl) ||
-                (SubIsOnLHS && ShiftOpcode1 == BinaryOperator::Shl);
   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
   Function *F = Intrinsic::getDeclaration(Trunc.getModule(), IID, DestTy);
   return IntrinsicInst::Create(F, { X, X, NarrowShAmt });