[llvm] r324122 - [InstCombine] simplify logic for swapMayExposeCSEOpportunities; NFCI

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Fri Feb  2 11:08:12 2018
New Revision: 324122

URL: http://llvm.org/viewvc/llvm-project?rev=324122&view=rev
Log:
[InstCombine] simplify logic for swapMayExposeCSEOpportunities; NFCI

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=324122&r1=324121&r2=324122&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Fri Feb  2 11:08:12 2018
@@ -3897,31 +3897,17 @@ static bool swapMayExposeCSEOpportunitie
   // FIXME: we may want to go through inttoptrs or bitcasts.
   if (Op0->getType()->isPointerTy())
     return false;
-  // Count all uses of both Op0 and Op1 in a subtract.
-  // Each time Op0 is the first operand, count -1: swapping is bad, the
-  // subtract has already the same layout as the compare.
-  // Each time Op0 is the second operand, count +1: swapping is good, the
-  // subtract has a different layout as the compare.
-  // At the end, if the benefit is greater than 0, Op0 should come second to
-  // expose more CSE opportunities.
-  int GlobalSwapBenefits = 0;
+  // If a subtract already has the same operands as a compare, swapping would be
+  // bad. If a subtract has the same operands as a compare but in reverse order,
+  // then swapping is good.
+  int GoodToSwap = 0;
   for (const User *U : Op0->users()) {
-    const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(U);
-    if (!BinOp || BinOp->getOpcode() != Instruction::Sub)
-      continue;
-    // If Op0 is the first argument, this is not beneficial to swap the
-    // arguments.
-    int LocalSwapBenefits = -1;
-    unsigned Op1Idx = 1;
-    if (BinOp->getOperand(Op1Idx) == Op0) {
-      Op1Idx = 0;
-      LocalSwapBenefits = 1;
-    }
-    if (BinOp->getOperand(Op1Idx) != Op1)
-      continue;
-    GlobalSwapBenefits += LocalSwapBenefits;
+    if (match(U, m_Sub(m_Specific(Op1), m_Specific(Op0))))
+      GoodToSwap++;
+    else if (match(U, m_Sub(m_Specific(Op0), m_Specific(Op1))))
+      GoodToSwap--;
   }
-  return GlobalSwapBenefits > 0;
+  return GoodToSwap > 0;
 }
 
 /// \brief Check that one use is in the same block as the definition and all