From: Sanjay Patel <spatel@rotateright.com>
Date: Fri, 2 Feb 2018 19:08:12 +0000 (+0000)
Subject: [InstCombine] simplify logic for swapMayExposeCSEOpportunities; NFCI
X-Git-Tag: android-x86-7.1-r4~5494
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=de02ec6d5b5f509066aee6a6df0f89489b22fe5a;p=android-x86%2Fexternal-llvm.git

[InstCombine] simplify logic for swapMayExposeCSEOpportunities; NFCI


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@324122 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 31e8dd23639..f90bb08b045 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3897,31 +3897,17 @@ static bool swapMayExposeCSEOpportunities(const Value *Op0, const Value *Op1) {
   // 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