Transform (X/Y)*Y into X if the division is exact. Instcombine already knows how

to do this and more, but would only do it if X/Y had only one use.  Spotted as the
most common missed simplification in SPEC by my auto-simplifier, now that it knows
about nuw/nsw/exact flags.  This removes a bunch of multiplications from 447.dealII
and 483.xalancbmk.  It also removes a lot from tramp3d-v4, which results in much
more inlining.

llvm-svn: 124560

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index cf50668cb01..fcbc6d50eeb 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -710,6 +710,15 @@ static Value *SimplifyMulInst(Value *Op0, Value *Op1, const TargetData *TD,
   if (match(Op1, m_One()))
     return Op0;
 
+  // (X / Y) * Y -> X if the division is exact.
+  Value *X = 0, *Y = 0;
+  if ((match(Op0, m_SDiv(m_Value(X), m_Value(Y))) && Y == Op1) || // (X / Y) * Y
+      (match(Op1, m_SDiv(m_Value(X), m_Value(Y))) && Y == Op0)) { // Y * (X / Y)
+    BinaryOperator *SDiv = cast<BinaryOperator>(Y == Op1 ? Op0 : Op1);
+    if (SDiv->isExact())
+      return X;
+  }
+
   // i1 mul -> and.
   if (MaxRecurse && Op0->getType()->isIntegerTy(1))
     if (Value *V = SimplifyAndInst(Op0, Op1, TD, DT, MaxRecurse-1))