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: [PATCH] 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 ++++++++++++++++++++
 test/Transforms/InstSimplify/call.ll | 51 ++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 34ff64d9004..4a3c74e9db3 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;
 
diff --git a/test/Transforms/InstSimplify/call.ll b/test/Transforms/InstSimplify/call.ll
index 1a8d0c25bd2..cf2f8476763 100644
--- a/test/Transforms/InstSimplify/call.ll
+++ b/test/Transforms/InstSimplify/call.ll
@@ -50,3 +50,54 @@ define float @test_fabs_libcall() {
   ret float %x
 ; CHECK-NEXT: ret float 4.2{{0+}}e+01
 }
+
+
+declare float @llvm.fabs.f32(float) nounwind readnone
+declare float @llvm.floor.f32(float) nounwind readnone
+declare float @llvm.ceil.f32(float) nounwind readnone
+declare float @llvm.trunc.f32(float) nounwind readnone
+declare float @llvm.rint.f32(float) nounwind readnone
+declare float @llvm.nearbyint.f32(float) nounwind readnone
+
+; Test idempotent intrinsics
+define float @test_idempotence(float %a) {
+; CHECK: @test_idempotence
+
+; CHECK: fabs
+; CHECK-NOT: fabs
+  %a0 = call float @llvm.fabs.f32(float %a)
+  %a1 = call float @llvm.fabs.f32(float %a0)
+
+; CHECK: floor
+; CHECK-NOT: floor
+  %b0 = call float @llvm.floor.f32(float %a)
+  %b1 = call float @llvm.floor.f32(float %b0)
+
+; CHECK: ceil
+; CHECK-NOT: ceil
+  %c0 = call float @llvm.ceil.f32(float %a)
+  %c1 = call float @llvm.ceil.f32(float %c0)
+
+; CHECK: trunc
+; CHECK-NOT: trunc
+  %d0 = call float @llvm.trunc.f32(float %a)
+  %d1 = call float @llvm.trunc.f32(float %d0)
+
+; CHECK: rint
+; CHECK-NOT: rint
+  %e0 = call float @llvm.rint.f32(float %a)
+  %e1 = call float @llvm.rint.f32(float %e0)
+
+; CHECK: nearbyint
+; CHECK-NOT: nearbyint
+  %f0 = call float @llvm.nearbyint.f32(float %a)
+  %f1 = call float @llvm.nearbyint.f32(float %f0)
+
+  %r0 = fadd float %a1, %b1
+  %r1 = fadd float %r0, %c1
+  %r2 = fadd float %r1, %d1
+  %r3 = fadd float %r2, %e1
+  %r4 = fadd float %r3, %f1
+
+  ret float %r4
+}