Fold fneg and fabs like multiplications

Given no NaNs and no signed zeroes it folds:

(fmul X, (select (fcmp X > 0.0), -1.0, 1.0)) -> (fneg (fabs X))
(fmul X, (select (fcmp X > 0.0), 1.0, -1.0)) -> (fabs X)

Differential Revision: https://reviews.llvm.org/D34579

llvm-svn: 306592

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/AMDGPU/fold-fmul-to-neg-abs.ll b/llvm/test/CodeGen/AMDGPU/fold-fmul-to-neg-abs.ll
new file mode 100644
index 00000000000..3637722d004
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/fold-fmul-to-neg-abs.ll
@@ -0,0 +1,37 @@
+; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=GCN %s
+
+; GCN-LABEL: {{^}}fold_mul_neg:
+; GCN: load_dword [[V:v[0-9]+]]
+; GCN: v_or_b32_e32 [[NEG:v[0-9]]], 0x80000000, [[V]]
+; GCN: store_dword [[NEG]]
+
+define amdgpu_kernel void @fold_mul_neg(float addrspace(1)* %arg) {
+  %tid = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %gep = getelementptr inbounds float, float addrspace(1)* %arg, i32 %tid
+  %v = load float, float addrspace(1)* %gep, align 4
+  %cmp = fcmp fast ogt float %v, 0.000000e+00
+  %sel = select i1 %cmp, float -1.000000e+00, float 1.000000e+00
+  %mul = fmul fast float %v, %sel
+  store float %mul, float addrspace(1)* %gep, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}fold_mul_abs:
+; GCN: load_dword [[V:v[0-9]+]]
+; GCN: v_and_b32_e32 [[ABS:v[0-9]]], 0x7fffffff, [[V]]
+; GCN: store_dword [[ABS]]
+
+define amdgpu_kernel void @fold_mul_abs(float addrspace(1)* %arg) {
+  %tid = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %gep = getelementptr inbounds float, float addrspace(1)* %arg, i32 %tid
+  %v = load float, float addrspace(1)* %gep, align 4
+  %cmp = fcmp fast olt float %v, 0.000000e+00
+  %sel = select i1 %cmp, float -1.000000e+00, float 1.000000e+00
+  %mul = fmul fast float %v, %sel
+  store float %mul, float addrspace(1)* %gep, align 4
+  ret void
+}
+
+declare i32 @llvm.amdgcn.workitem.id.x() #0
+
+attributes #0 = { nounwind readnone speculatable }