1 files changed, 10 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp b/contrib/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp
index f352fa6..58d3c3d 100644
--- a/contrib/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp
+++ b/contrib/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp
@@ -136,6 +136,16 @@ protected:
         // source of the copy, it must still be live here.  We can't use
         // interval testing for a physical register, so as long as we're
         // walking the MIs we may as well test liveness here.
+        //
+        // FIXME: There is a case that occurs in practice, like this:
+        //   %vreg9<def> = COPY %F1; VSSRC:%vreg9
+        //   ...
+        //   %vreg6<def> = COPY %vreg9; VSSRC:%vreg6,%vreg9
+        //   %vreg7<def> = COPY %vreg9; VSSRC:%vreg7,%vreg9
+        //   %vreg9<def,tied1> = XSMADDASP %vreg9<tied0>, %vreg1, %vreg4; VSSRC:
+        //   %vreg6<def,tied1> = XSMADDASP %vreg6<tied0>, %vreg1, %vreg2; VSSRC:
+        //   %vreg7<def,tied1> = XSMADDASP %vreg7<tied0>, %vreg1, %vreg3; VSSRC:
+        // which prevents an otherwise-profitable transformation.
         bool OtherUsers = false, KillsAddendSrc = false;
         for (auto J = std::prev(I), JE = MachineBasicBlock::iterator(AddendMI);
              J != JE; --J) {