Add intrinsics for float arithmetic with `fast` flag enabled

`fast` a.k.a UnsafeAlgebra is the flag for enabling all "unsafe"
(according to llvm) float optimizations.

See LangRef for more information http://llvm.org/docs/LangRef.html#fast-math-flags

Providing these operations with less precise associativity rules (for
example) is useful to numerical applications.

For example, the summation loop:

    let sum = 0.;
    for element in data {
        sum += *element;
    }

Using the default floating point semantics, this loop expresses the
floats must be added in a sequence, one after another. This constraint
is usually completely unintended, and it means that no autovectorization
is possible.

1 files changed, 60 insertions, 0 deletions

diff --git a/src/test/codegen/float_math.rs b/src/test/codegen/float_math.rs
new file mode 100644
index 00000000000..bc458d45446
--- /dev/null
+++ b/src/test/codegen/float_math.rs
@@ -0,0 +1,60 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+#![feature(core_intrinsics)]
+
+use std::intrinsics::{fadd_fast, fsub_fast, fmul_fast, fdiv_fast, frem_fast};
+
+// CHECK-LABEL: @add
+#[no_mangle]
+pub fn add(x: f32, y: f32) -> f32 {
+// CHECK: fadd float
+// CHECK-NOT fast
+    x + y
+}
+
+// CHECK-LABEL: @addition
+#[no_mangle]
+pub fn addition(x: f32, y: f32) -> f32 {
+// CHECK: fadd fast float
+    unsafe {
+        fadd_fast(x, y)
+    }
+}
+
+// CHECK-LABEL: @subtraction
+#[no_mangle]
+pub fn subtraction(x: f32, y: f32) -> f32 {
+// CHECK: fsub fast float
+    unsafe {
+        fsub_fast(x, y)
+    }
+}
+
+// CHECK-LABEL: @multiplication
+#[no_mangle]
+pub fn multiplication(x: f32, y: f32) -> f32 {
+// CHECK: fmul fast float
+    unsafe {
+        fmul_fast(x, y)
+    }
+}
+
+// CHECK-LABEL: @division
+#[no_mangle]
+pub fn division(x: f32, y: f32) -> f32 {
+// CHECK: fdiv fast float
+    unsafe {
+        fdiv_fast(x, y)
+    }
+}