From 05044c248e640118ae8b7870b94bf127bb23ef73 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 6 Dec 2014 00:45:50 +0000
Subject: [PATCH] Canonicalize multiplies by looking at whether the operands
 have any constants themselves. Patch by Tim Murray!

llvm-svn: 223554
---
 llvm/lib/Analysis/ScalarEvolution.cpp | 31 ++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 68549efad501..792542eab255 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2207,6 +2207,25 @@ static uint64_t Choose(uint64_t n, uint64_t k, bool &Overflow) {
   return r;
 }
 
+/// Determine if any of the operands in this SCEV are a constant or if
+/// any of the add or multiply expressions in this SCEV contain a constant.
+static bool containsConstantSomewhere(const SCEV *StartExpr) {
+  SmallVector<const SCEV *, 4> Ops;
+  Ops.push_back(StartExpr);
+  while (!Ops.empty()) {
+    const SCEV *CurrentExpr = Ops.pop_back_val();
+    if (isa<SCEVConstant>(*CurrentExpr))
+      return true;
+
+    if (isa<SCEVAddExpr>(*CurrentExpr) || isa<SCEVMulExpr>(*CurrentExpr)) {
+      const auto *CurrentNAry = cast<SCEVNAryExpr>(CurrentExpr);
+      for (const SCEV *Operand : CurrentNAry->operands())
+        Ops.push_back(Operand);
+    }
+  }
+  return false;
+}
+
 /// getMulExpr - Get a canonical multiply expression, or something simpler if
 /// possible.
 const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
@@ -2246,11 +2265,13 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
 
     // C1*(C2+V) -> C1*C2 + C1*V
     if (Ops.size() == 2)
-      if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1]))
-        if (Add->getNumOperands() == 2 &&
-            isa<SCEVConstant>(Add->getOperand(0)))
-          return getAddExpr(getMulExpr(LHSC, Add->getOperand(0)),
-                            getMulExpr(LHSC, Add->getOperand(1)));
+        if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1]))
+          // If any of Add's ops are Adds or Muls with a constant,
+          // apply this transformation as well.
+          if (Add->getNumOperands() == 2)
+            if (containsConstantSomewhere(Add))
+              return getAddExpr(getMulExpr(LHSC, Add->getOperand(0)),
+                                getMulExpr(LHSC, Add->getOperand(1)));
 
     ++Idx;
     while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {