From f89de816ae5cf2d0dad7869882dd626532b934ef Mon Sep 17 00:00:00 2001
From: Michael Ilseman <milseman@apple.com>
Date: Thu, 7 Feb 2013 19:26:05 +0000
Subject: Identify and simplify idempotent intrinsics. Test case included.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174650 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/InstructionSimplify.cpp | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

(limited to 'lib/Analysis/InstructionSimplify.cpp')

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 34ff64d900..4a3c74e9db 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -2925,6 +2925,37 @@ Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
                            RecursionLimit);
 }
 
+static bool IsIdempotent(Intrinsic::ID ID) {
+  switch (ID) {
+  default: return false;
+
+  // Unary idempotent: f(f(x)) = f(x)
+  case Intrinsic::fabs:
+  case Intrinsic::floor:
+  case Intrinsic::ceil:
+  case Intrinsic::trunc:
+  case Intrinsic::rint:
+  case Intrinsic::nearbyint:
+    return true;
+  }
+}
+
+template <typename IterTy>
+static Value *SimplifyIntrinsic(Intrinsic::ID IID, IterTy ArgBegin, IterTy ArgEnd,
+                                const Query &Q, unsigned MaxRecurse) {
+  // Perform idempotent optimizations
+  if (!IsIdempotent(IID))
+    return 0;
+
+  // Unary Ops
+  if (std::distance(ArgBegin, ArgEnd) == 1)
+    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(*ArgBegin))
+      if (II->getIntrinsicID() == IID)
+        return II;
+
+  return 0;
+}
+
 template <typename IterTy>
 static Value *SimplifyCall(Value *V, IterTy ArgBegin, IterTy ArgEnd,
                            const Query &Q, unsigned MaxRecurse) {
@@ -2941,6 +2972,11 @@ static Value *SimplifyCall(Value *V, IterTy ArgBegin, IterTy ArgEnd,
   if (!F)
     return 0;
 
+  if (unsigned IID = F->getIntrinsicID())
+    if (Value *Ret =
+        SimplifyIntrinsic((Intrinsic::ID) IID, ArgBegin, ArgEnd, Q, MaxRecurse))
+      return Ret;
+
   if (!canConstantFoldCallTo(F))
     return 0;
 
-- 
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