[PowerPC] add fsub-fneg test; NFC

This is a test for a transform that was suggested in the post-commit
mailing list thread for rL329821. The target in question is not in
trunk, so PPC gets to stand in for it because it's the only in-tree
target that sets 'isFPExtFree()' to 'true'.

llvm-svn: 329963

llvm/test/CodeGen/PowerPC/fsub-fneg.ll

@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le < %s | FileCheck %s
+
+; FIXME: When fpext is free, we should look through it for optimizations
+; even if it has multiple uses and produce an 'fadd' here.
+; Y - (fpext(-X)) --> Y + fpext(X)
+
+define double @neg_ext_op1_extra_use(float %x, double %y) nounwind {
+; CHECK-LABEL: neg_ext_op1_extra_use:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    fneg 0, 1
+; CHECK-NEXT:    xssubdp 1, 2, 0
+; CHECK-NEXT:    xsdivdp 1, 0, 1
+; CHECK-NEXT:    blr
+  %t1 = fsub float -0.0, %x
+  %t2 = fpext float %t1 to double
+  %t3 = fsub double %y, %t2
+  %t4 = fdiv double %t2, %t3
+  ret double %t4
+}
+