[SimplifyLibCalls] New transformation: tan(atan(x)) -> x

This is enabled only under -ffast-math.
So, instead of emitting:
  4007b0:       50                      push   %rax
  4007b1:       e8 8a fd ff ff          callq  400540 <atanf@plt>
  4007b6:       58                      pop    %rax
  4007b7:       e9 94 fd ff ff          jmpq   400550 <tanf@plt>
  4007bc:       0f 1f 40 00             nopl   0x0(%rax)

for:
float mytan(float x) {
  return tanf(atanf(x));
}
we emit a single retq.

Differential Revision:	 http://reviews.llvm.org/D14302


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252098 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Transforms/Utils/SimplifyLibCalls.h

@@ -134,6 +134,7 @@ private:
   Value *optimizeFMinFMax(CallInst *CI, IRBuilder<> &B);
   Value *optimizeSqrt(CallInst *CI, IRBuilder<> &B);
   Value *optimizeSinCosPi(CallInst *CI, IRBuilder<> &B);
+  Value *optimizeTan(CallInst *CI, IRBuilder<> &B);
 
   // Integer Library Call Optimizations
   Value *optimizeFFS(CallInst *CI, IRBuilder<> &B);

lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -1359,6 +1359,40 @@ Value *LibCallSimplifier::optimizeSqrt(CallInst *CI, IRBuilder<> &B) {
   return Ret;
 }
 
+Value *LibCallSimplifier::optimizeTan(CallInst *CI, IRBuilder<> &B) {
+  Function *Callee = CI->getCalledFunction();
+  Value *Ret = nullptr;
+  if (UnsafeFPShrink && Callee->getName() == "tan" && TLI->has(LibFunc::tanf))
+    Ret = optimizeUnaryDoubleFP(CI, B, true);
+  FunctionType *FT = Callee->getFunctionType();
+
+  // Just make sure this has 1 argument of FP type, which matches the
+  // result type.
+  if (FT->getNumParams() != 1 || FT->getReturnType() != FT->getParamType(0) ||
+      !FT->getParamType(0)->isFloatingPointTy())
+    return Ret;
+
+  if (!canUseUnsafeFPMath(CI->getParent()->getParent()))
+    return Ret;
+  Value *Op1 = CI->getArgOperand(0);
+  auto *OpC = dyn_cast<CallInst>(Op1);
+  if (!OpC)
+    return Ret;
+
+  // tan(atan(x)) -> x
+  // tanf(atanf(x)) -> x
+  // tanl(atanl(x)) -> x
+  LibFunc::Func Func;
+  Function *F = OpC->getCalledFunction();
+  StringRef FuncName = F->getName();
+  if (TLI->getLibFunc(FuncName, Func) && TLI->has(Func) &&
+      ((Func == LibFunc::atan && Callee->getName() == "tan") ||
+       (Func == LibFunc::atanf && Callee->getName() == "tanf") ||
+       (Func == LibFunc::atanl && Callee->getName() == "tanl")))
+    Ret = OpC->getArgOperand(0);
+  return Ret;
+}
+
 static bool isTrigLibCall(CallInst *CI);
 static void insertSinCosCall(IRBuilder<> &B, Function *OrigCallee, Value *Arg,
                              bool UseFloat, Value *&Sin, Value *&Cos,
@@ -2146,6 +2180,10 @@ Value *LibCallSimplifier::optimizeCall(CallInst *CI) {
       return optimizeFPuts(CI, Builder);
     case LibFunc::puts:
       return optimizePuts(CI, Builder);
+    case LibFunc::tan:
+    case LibFunc::tanf:
+    case LibFunc::tanl:
+      return optimizeTan(CI, Builder);
     case LibFunc::perror:
       return optimizeErrorReporting(CI, Builder);
     case LibFunc::vfprintf:
@@ -2180,7 +2218,6 @@ Value *LibCallSimplifier::optimizeCall(CallInst *CI) {
     case LibFunc::logb:
     case LibFunc::sin:
     case LibFunc::sinh:
-    case LibFunc::tan:
     case LibFunc::tanh:
       if (UnsafeFPShrink && hasFloatVersion(FuncName))
         return optimizeUnaryDoubleFP(CI, Builder, true);

test/Transforms/InstCombine/tan-nofastmath.ll

@@ -0,0 +1,17 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define float @mytan(float %x) {
+entry:
+  %call = call float @atanf(float %x)
+  %call1 = call float @tanf(float %call) 
+  ret float %call1
+}
+
+; CHECK-LABEL: define float @mytan(
+; CHECK:   %call = call float @atanf(float %x)
+; CHECK-NEXT:   %call1 = call float @tanf(float %call)
+; CHECK-NEXT:   ret float %call1
+; CHECK-NEXT: }
+
+declare float @tanf(float)
+declare float @atanf(float)

test/Transforms/InstCombine/tan.ll

@@ -0,0 +1,15 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define float @mytan(float %x) #0 {
+entry:
+  %call = call float @atanf(float %x)
+  %call1 = call float @tanf(float %call)
+  ret float %call1
+}
+
+; CHECK-LABEL: define float @mytan(
+; CHECK:   ret float %x
+
+declare float @tanf(float) #0
+declare float @atanf(float) #0
+attributes #0 = { "unsafe-fp-math"="true" }