Convert floating point division by a constant into multiplication by the

reciprocal if converting to the reciprocal is exact.  Do it even if inexact
if -ffast-math.  This substantially speeds up ac.f90 from the polyhedron
benchmarks.

llvm-svn: 154265

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/fdiv.ll b/llvm/test/CodeGen/X86/fdiv.ll
new file mode 100644
index 00000000000..553f14efa13
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fdiv.ll
@@ -0,0 +1,32 @@
+; RUN: llc < %s -march=x86-64 | FileCheck %s
+; RUN: llc < %s -march=x86-64 -enable-unsafe-fp-math | FileCheck -check-prefix=UNSAFE %s
+
+define double @exact(double %x) {
+; Exact division by a constant always converted to multiplication.
+; CHECK: @exact
+; CHECK: mulsd
+; UNSAFE: @exact
+; UNSAFE: mulsd
+  %div = fdiv double %x, 2.0
+  ret double %div
+}
+
+define double @inexact(double %x) {
+; Inexact division by a constant converted to multiplication if unsafe-math.
+; CHECK: @inexact
+; CHECK: divsd
+; UNSAFE: @inexact
+; UNSAFE: mulsd
+  %div = fdiv double %x, 0x41DFFFFFFFC00000 
+  ret double %div
+}
+
+define double @funky(double %x) {
+; No conversion to multiplication if too funky.
+; CHECK: @funky
+; CHECK: divsd
+; UNSAFE: @funky
+; UNSAFE: divsd
+  %div = fdiv double %x, 0.0
+  ret double %div
+}