instcombine: Migrate *abs optimizations

This patch migrates the *abs optimizations from the simplify-libcalls
pass into the instcombine library call simplifier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168574 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index dd623dc..ec98e93 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1250,6 +1250,23 @@ struct FFSOpt : public LibCallOptimization {
   }
 };
 
+struct AbsOpt : public LibCallOptimization {
+  virtual Value *callOptimizer(Function *Callee, CallInst *CI, IRBuilder<> &B) {
+    FunctionType *FT = Callee->getFunctionType();
+    // We require integer(integer) where the types agree.
+    if (FT->getNumParams() != 1 || !FT->getReturnType()->isIntegerTy() ||
+        FT->getParamType(0) != FT->getReturnType())
+      return 0;
+
+    // abs(x) -> x >s -1 ? x : -x
+    Value *Op = CI->getArgOperand(0);
+    Value *Pos = B.CreateICmpSGT(Op, Constant::getAllOnesValue(Op->getType()),
+                                 "ispos");
+    Value *Neg = B.CreateNeg(Op, "neg");
+    return B.CreateSelect(Pos, Op, Neg);
+  }
+};
+
 } // End anonymous namespace.
 
 namespace llvm {
@@ -1298,6 +1315,7 @@ class LibCallSimplifierImpl {
 
   // Integer library call optimizations.
   FFSOpt FFS;
+  AbsOpt Abs;
 
   void initOptimizations();
   void addOpt(LibFunc::Func F, LibCallOptimization* Opt);
@@ -1413,6 +1431,9 @@ void LibCallSimplifierImpl::initOptimizations() {
   addOpt(LibFunc::ffs, &FFS);
   addOpt(LibFunc::ffsl, &FFS);
   addOpt(LibFunc::ffsll, &FFS);
+  addOpt(LibFunc::abs, &Abs);
+  addOpt(LibFunc::labs, &Abs);
+  addOpt(LibFunc::llabs, &Abs);
 }
 
 Value *LibCallSimplifierImpl::optimizeCall(CallInst *CI) {