[llvm] 981fdf0 - [InstCombine] foldSelectRotate - canonicalize to OR(SHL,LSHR). NFCI.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-10-16T13:18:53+01:00
New Revision: 981fdf01d527e890e158c32bdc3c1a1bef731abf

URL: https://github.com/llvm/llvm-project/commit/981fdf01d527e890e158c32bdc3c1a1bef731abf
DIFF: https://github.com/llvm/llvm-project/commit/981fdf01d527e890e158c32bdc3c1a1bef731abf.diff

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

Match the canonicalization code that was added to matchFunnelShift at rG02295e6d1a15

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 55266ff7c7eb..b8d4dddbfd15 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2337,8 +2337,8 @@ static Instruction *factorizeMinMaxTree(SelectPatternFlavor SPF, Value *LHS,
 static Instruction *foldSelectRotate(SelectInst &Sel,
                                      InstCombiner::BuilderTy &Builder) {
   // The false value of the select must be a rotate of the true value.
-  Value *Or0, *Or1;
-  if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
+  BinaryOperator *Or0, *Or1;
+  if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
     return nullptr;
 
   Value *TVal = Sel.getTrueValue();
@@ -2346,16 +2346,20 @@ static Instruction *foldSelectRotate(SelectInst &Sel,
   if (!match(Or0, m_OneUse(m_LogicalShift(m_Specific(TVal),
                                           m_ZExtOrSelf(m_Value(SA0))))) ||
       !match(Or1, m_OneUse(m_LogicalShift(m_Specific(TVal),
-                                          m_ZExtOrSelf(m_Value(SA1))))))
+                                          m_ZExtOrSelf(m_Value(SA1))))) ||
+      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(TVal, SA0), lshr(TVal, SA1)).
+  if (Or0->getOpcode() == BinaryOperator::LShr) {
+    std::swap(Or0, Or1);
+    std::swap(SA0, SA1);
+  }
+  assert(Or0->getOpcode() == BinaryOperator::Shl &&
+         Or1->getOpcode() == BinaryOperator::LShr &&
+         "Illegal or(shift,shift) pair");
 
-  // We have one of these patterns so far:
-  // select ?, TVal, (or (lshr TVal, SA0), (shl TVal, SA1))
+  // We should now have this pattern:
   // select ?, TVal, (or (shl TVal, SA0), (lshr TVal, SA1))
   // This must be a power-of-2 rotate for a bitmasking transform to be valid.
   unsigned Width = Sel.getType()->getScalarSizeInBits();
@@ -2380,8 +2384,7 @@ static Instruction *foldSelectRotate(SelectInst &Sel,
 
   // This is a rotate that avoids shift-by-bitwidth UB in a suboptimal way.
   // Convert to funnel shift intrinsic.
-  bool IsFshl = (ShAmt == SA0 && ShiftOpcode0 == BinaryOperator::Shl) ||
-                (ShAmt == SA1 && ShiftOpcode1 == BinaryOperator::Shl);
+  bool IsFshl = (ShAmt == SA0);
   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
   Function *F = Intrinsic::getDeclaration(Sel.getModule(), IID, Sel.getType());
   ShAmt = Builder.CreateZExt(ShAmt, Sel.getType());