transform obscured FP sign bit ops into a fabs/fneg using TLI hook

This is effectively a revert of:
http://reviews.llvm.org/rL249702 - [InstCombine] transform masking off of an FP sign bit into a fabs() intrinsic call (PR24886)
and:
http://reviews.llvm.org/rL249701 - [ValueTracking] teach computeKnownBits that a fabs() clears sign bits
and a reimplementation as a DAG combine for targets that have IEEE754-compliant fabs/fneg instructions.

This is intended to resolve the objections raised on the dev list:
http://lists.llvm.org/pipermail/llvm-dev/2016-April/098154.html
and:
https://llvm.org/bugs/show_bug.cgi?id=24886#c4

In the interest of patch minimalism, I've only partly enabled AArch64. PowerPC, MIPS, x86 and others can enable later.

Differential Revision: http://reviews.llvm.org/D19391

llvm-svn: 271573

1 files changed, 0 insertions, 25 deletions

diff --git a/llvm/test/Transforms/InstCombine/fabs.ll b/llvm/test/Transforms/InstCombine/fabs.ll
index 941270df0e9..0479549bea3 100644
--- a/llvm/test/Transforms/InstCombine/fabs.ll
+++ b/llvm/test/Transforms/InstCombine/fabs.ll
@@ -41,7 +41,6 @@ define fp128 @square_fabs_call_f128(fp128 %x) {
 declare float @llvm.fabs.f32(float)
 declare double @llvm.fabs.f64(double)
 declare fp128 @llvm.fabs.f128(fp128)
-declare <4 x float> @llvm.fabs.v4f32(<4 x float>)
 
 define float @square_fabs_intrinsic_f32(float %x) {
   %mul = fmul float %x, %x
@@ -99,27 +98,3 @@ define float @square_fabs_shrink_call2(float %x) {
 ; CHECK-NEXT: ret float %sq
 }
 
-; A scalar fabs op makes the sign bit zero, so masking off all of the other bits means we can return zero.
-
-define i32 @fabs_value_tracking_f32(float %x) {
-  %call = call float @llvm.fabs.f32(float %x)
-  %bc = bitcast float %call to i32
-  %and = and i32 %bc, 2147483648
-  ret i32 %and
-
-; CHECK-LABEL: fabs_value_tracking_f32(
-; CHECK:       ret i32 0
-}
-
-; TODO: A vector fabs op makes the sign bits zero, so masking off all of the other bits means we can return zero.
-
-define <4 x i32> @fabs_value_tracking_v4f32(<4 x float> %x) {
-  %call = call <4 x float> @llvm.fabs.v4f32(<4 x float> %x)
-  %bc = bitcast <4 x float> %call to <4 x i32>
-  %and = and <4 x i32> %bc, <i32 2147483648, i32 2147483648, i32 2147483648, i32 2147483648>
-  ret <4 x i32> %and
-
-; CHECK-LABEL: fabs_value_tracking_v4f32(
-; CHECK:       ret <4 x i32> %and
-}
-