Use PPC reciprocal estimates with Newton iteration in fast-math mode

When unsafe FP math operations are enabled, we can use the fre[s] and
frsqrte[s] instructions, which generate reciprocal (sqrt) estimates, together
with some Newton iteration, in order to quickly generate floating-point
division and sqrt results. All of these instructions are separately optional,
and so each has its own feature flag (except for the Altivec instructions,
which are covered under the existing Altivec flag). Doing this is not only
faster than using the IEEE-compliant fdiv/fsqrt instructions, but allows these
computations to be pipelined with other computations in order to hide their
overall latency.

I've also added a couple of missing fnmsub patterns which turned out to be
missing (but are necessary for good code generation of the Newton iterations).
Altivec needs a similar fix, but that will probably be more complicated because
fneg is expanded for Altivec's v4f32.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178617 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 178 insertions, 0 deletions

diff --git a/test/CodeGen/PowerPC/recipest.ll b/test/CodeGen/PowerPC/recipest.ll
new file mode 100644
index 0000000000..cad98c5a35
--- /dev/null
+++ b/test/CodeGen/PowerPC/recipest.ll
@@ -0,0 +1,178 @@
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -enable-unsafe-fp-math | FileCheck %s
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 | FileCheck -check-prefix=CHECK-SAFE %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+declare double @llvm.sqrt.f64(double)
+declare float @llvm.sqrt.f32(float)
+declare <4 x float> @llvm.sqrt.v4f32(<4 x float>)
+
+define double @foo(double %a, double %b) nounwind {
+entry:
+  %x = call double @llvm.sqrt.f64(double %b)
+  %r = fdiv double %a, %x
+  ret double %r
+
+; CHECK: @foo
+; CHECK: frsqrte
+; CHECK: fnmsub
+; CHECK: fmul
+; CHECK: fmadd
+; CHECK: fmul
+; CHECK: fmul
+; CHECK: fmadd
+; CHECK: fmul
+; CHECK: fmul
+; CHECK: blr
+
+; CHECK-SAFE: @foo
+; CHECK-SAFE: fsqrt
+; CHECK-SAFE: fdiv
+; CHECK-SAFE: blr
+}
+
+define float @goo(float %a, float %b) nounwind {
+entry:
+  %x = call float @llvm.sqrt.f32(float %b)
+  %r = fdiv float %a, %x
+  ret float %r
+
+; CHECK: @goo
+; CHECK: frsqrtes
+; CHECK: fnmsubs
+; CHECK: fmuls
+; CHECK: fmadds
+; CHECK: fmuls
+; CHECK: fmuls
+; CHECK: blr
+
+; CHECK-SAFE: @goo
+; CHECK-SAFE: fsqrts
+; CHECK-SAFE: fdivs
+; CHECK-SAFE: blr
+}
+
+define <4 x float> @hoo(<4 x float> %a, <4 x float> %b) nounwind {
+entry:
+  %x = call <4 x float> @llvm.sqrt.v4f32(<4 x float> %b)
+  %r = fdiv <4 x float> %a, %x
+  ret <4 x float> %r
+
+; CHECK: @hoo
+; CHECK: vrsqrtefp
+
+; CHECK-SAFE: @hoo
+; CHECK-SAFE-NOT: vrsqrtefp
+; CHECK-SAFE: blr
+}
+
+define double @foo2(double %a, double %b) nounwind {
+entry:
+  %r = fdiv double %a, %b
+  ret double %r
+
+; CHECK: @foo2
+; CHECK: fre
+; CHECK: fnmsub
+; CHECK: fmadd
+; CHECK: fnmsub
+; CHECK: fmadd
+; CHECK: fmul
+; CHECK: blr
+
+; CHECK-SAFE: @foo2
+; CHECK-SAFE: fdiv
+; CHECK-SAFE: blr
+}
+
+define float @goo2(float %a, float %b) nounwind {
+entry:
+  %r = fdiv float %a, %b
+  ret float %r
+
+; CHECK: @goo2
+; CHECK: fres
+; CHECK: fnmsubs
+; CHECK: fmadds
+; CHECK: fmuls
+; CHECK: blr
+
+; CHECK-SAFE: @goo2
+; CHECK-SAFE: fdivs
+; CHECK-SAFE: blr
+}
+
+define <4 x float> @hoo2(<4 x float> %a, <4 x float> %b) nounwind {
+entry:
+  %r = fdiv <4 x float> %a, %b
+  ret <4 x float> %r
+
+; CHECK: @hoo2
+; CHECK: vrefp
+
+; CHECK-SAFE: @hoo2
+; CHECK-SAFE-NOT: vrefp
+; CHECK-SAFE: blr
+}
+
+define double @foo3(double %a) nounwind {
+entry:
+  %r = call double @llvm.sqrt.f64(double %a)
+  ret double %r
+
+; CHECK: @foo3
+; CHECK: frsqrte
+; CHECK: fnmsub
+; CHECK: fmul
+; CHECK: fmadd
+; CHECK: fmul
+; CHECK: fmul
+; CHECK: fmadd
+; CHECK: fmul
+; CHECK: fre
+; CHECK: fnmsub
+; CHECK: fmadd
+; CHECK: fnmsub
+; CHECK: fmadd
+; CHECK: blr
+
+; CHECK-SAFE: @foo3
+; CHECK-SAFE: fsqrt
+; CHECK-SAFE: blr
+}
+
+define float @goo3(float %a) nounwind {
+entry:
+  %r = call float @llvm.sqrt.f32(float %a)
+  ret float %r
+
+; CHECK: @goo3
+; CHECK: frsqrtes
+; CHECK: fnmsubs
+; CHECK: fmuls
+; CHECK: fmadds
+; CHECK: fmuls
+; CHECK: fres
+; CHECK: fnmsubs
+; CHECK: fmadds
+; CHECK: blr
+
+; CHECK-SAFE: @goo3
+; CHECK-SAFE: fsqrts
+; CHECK-SAFE: blr
+}
+
+define <4 x float> @hoo3(<4 x float> %a) nounwind {
+entry:
+  %r = call <4 x float> @llvm.sqrt.v4f32(<4 x float> %a)
+  ret <4 x float> %r
+
+; CHECK: @hoo3
+; CHECK: vrsqrtefp
+; CHECK: vrefp
+
+; CHECK-SAFE: @hoo3
+; CHECK-SAFE-NOT: vrsqrtefp
+; CHECK-SAFE: blr
+}
+