From 798a5f70df9a9f7f486a71152ddf6ee572e3d9cc Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Tue, 8 Nov 2016 11:53:26 +0000
Subject: [PATCH] Revert "runtime: remove some redundant libm functions copied
 inline."

This reverts commit fee75bd50f9240b7b0377291718d7354498c9b62.

LLVM does not have lround as a libcall and this inhibits LICM.
---
 .../compiler/transforms/llvm_ir_generator.py  |  9 +++---
 artiq/runtime.rs/libksupport/api.rs           |  2 +-
 artiq/runtime/ksupport_glue.c                 | 29 +++++++++++++++++--
 3 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
index e9643aa04..c86888a0f 100644
--- a/artiq/compiler/transforms/llvm_ir_generator.py
+++ b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -323,6 +323,8 @@ class LLVMIRGenerator:
             llty = ll.FunctionType(llvoid, [])
         elif name == "llvm.floor.f64":
             llty = ll.FunctionType(lldouble, [lldouble])
+        elif name == "llvm.round.f64":
+            llty = ll.FunctionType(lldouble, [lldouble])
         elif name == "llvm.pow.f64":
             llty = ll.FunctionType(lldouble, [lldouble, lldouble])
         elif name == "llvm.powi.f64":
@@ -347,8 +349,6 @@ class LLVMIRGenerator:
             llty = ll.FunctionType(lli32, [llptr])
         elif name == "strcmp":
             llty = ll.FunctionType(lli32, [llptr, llptr])
-        elif name == "lround":
-            llty = ll.FunctionType(lli32, [lldouble])
         elif name == "send_rpc":
             llty = ll.FunctionType(llvoid, [lli32, llptr, llptrptr])
         elif name == "send_async_rpc":
@@ -1044,8 +1044,9 @@ class LLVMIRGenerator:
                                          name=insn.name)
         elif insn.op == "round":
             llarg = self.map(insn.operands[0])
-            return self.llbuilder.call(self.llbuiltin("lround"), [llarg],
-                                       name=insn.name)
+            llvalue = self.llbuilder.call(self.llbuiltin("llvm.round.f64"), [llarg])
+            return self.llbuilder.fptosi(llvalue, self.llty_of_type(insn.type),
+                                         name=insn.name)
         elif insn.op == "globalenv":
             def get_outer(llenv, env_ty):
                 if "$outer" in env_ty.params:
diff --git a/artiq/runtime.rs/libksupport/api.rs b/artiq/runtime.rs/libksupport/api.rs
index 81c4d75df..5f9d7f967 100644
--- a/artiq/runtime.rs/libksupport/api.rs
+++ b/artiq/runtime.rs/libksupport/api.rs
@@ -74,7 +74,7 @@ static mut API: &'static [(&'static str, *const ())] = &[
 
     /* libm */
     api!(sqrt),
-    api!(lround),
+    api!(round),
 
     /* exceptions */
     api!(_Unwind_Resume),
diff --git a/artiq/runtime/ksupport_glue.c b/artiq/runtime/ksupport_glue.c
index 515635c94..f0d496dc3 100644
--- a/artiq/runtime/ksupport_glue.c
+++ b/artiq/runtime/ksupport_glue.c
@@ -70,10 +70,33 @@ int dl_iterate_phdr (int (*callback)(struct dl_phdr_info *, size_t, void *), voi
 }
 
 /* called by kernel */
-long lround(double x);
-long lround(double x)
+double round(double x);
+double round(double x)
 {
-    return x < 0 ? floor(x) : ceil(x);
+    union {double f; uint64_t i;} u = {x};
+    int e = u.i >> 52 & 0x7ff;
+    double y;
+
+    if (e >= 0x3ff+52)
+        return x;
+    if (u.i >> 63)
+        x = -x;
+    if (e < 0x3ff-1) {
+        /* we don't do it in ARTIQ */
+        /* raise inexact if x!=0 */
+        // FORCE_EVAL(x + 0x1p52);
+        return 0*u.f;
+    }
+    y = (double)(x + 0x1p52) - 0x1p52 - x;
+    if (y > 0.5)
+        y = y + x - 1;
+    else if (y <= -0.5)
+        y = y + x + 1;
+    else
+        y = y + x;
+    if (u.i >> 63)
+        y = -y;
+    return y;
 }
 
 /* called by kernel */