From 6a832715325f740a0e78acd194abad9104389075 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Sun, 29 Aug 2010 15:27:08 +0000
Subject: [PATCH] Add some comments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112437 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index ad87fcaaa4c..d3d17a96527 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1932,20 +1932,25 @@ void LSRInstance::DeleteUse(LSRUse &LU) {
 LSRUse *
 LSRInstance::FindUseWithSimilarFormula(const Formula &OrigF,
                                        const LSRUse &OrigLU) {
-  // Search all uses for the formula. This could be more clever. Ignore
-  // ICmpZero uses because they may contain formulae generated by
-  // GenerateICmpZeroScales, in which case adding fixup offsets may
-  // be invalid.
+  // Search all uses for the formula. This could be more clever.
   for (size_t LUIdx = 0, NumUses = Uses.size(); LUIdx != NumUses; ++LUIdx) {
     LSRUse &LU = Uses[LUIdx];
+    // Check whether this use is close enough to OrigLU, to see whether it's
+    // worthwhile looking through its formulae.
+    // Ignore ICmpZero uses because they may contain formulae generated by
+    // GenerateICmpZeroScales, in which case adding fixup offsets may
+    // be invalid.
     if (&LU != &OrigLU &&
         LU.Kind != LSRUse::ICmpZero &&
         LU.Kind == OrigLU.Kind && OrigLU.AccessTy == LU.AccessTy &&
         LU.WidestFixupType == OrigLU.WidestFixupType &&
         LU.HasFormulaWithSameRegs(OrigF)) {
+      // Scan through this use's formulae.
       for (SmallVectorImpl<Formula>::const_iterator I = LU.Formulae.begin(),
            E = LU.Formulae.end(); I != E; ++I) {
         const Formula &F = *I;
+        // Check to see if this formula has the same registers and symbols
+        // as OrigF.
         if (F.BaseRegs == OrigF.BaseRegs &&
             F.ScaledReg == OrigF.ScaledReg &&
             F.AM.BaseGV == OrigF.AM.BaseGV &&
@@ -1953,12 +1958,16 @@ LSRInstance::FindUseWithSimilarFormula(const Formula &OrigF,
             LU.Kind) {
           if (F.AM.BaseOffs == 0)
             return &LU;
+          // This is the formula where all the registers and symbols matched;
+          // there aren't going to be any others. Since we declined it, we
+          // can skip the rest of the formulae and procede to the next LSRUse.
           break;
         }
       }
     }
   }
 
+  // Nothing looked good.
   return 0;
 }