[PowerPC] fma chain break to expose more ILP

This patch tries to reassociate two patterns related to FMA to expose
more ILP on PowerPC.

// Pattern 1:
//   A =  FADD X,  Y          (Leaf)
//   B =  FMA  A,  M21,  M22  (Prev)
//   C =  FMA  B,  M31,  M32  (Root)
// -->
//   A =  FMA  X,  M21,  M22
//   B =  FMA  Y,  M31,  M32
//   C =  FADD A,  B

// Pattern 2:
//   A =  FMA  X,  M11,  M12  (Leaf)
//   B =  FMA  A,  M21,  M22  (Prev)
//   C =  FMA  B,  M31,  M32  (Root)
// -->
//   A =  FMUL M11,  M12
//   B =  FMA  X,  M21,  M22
//   D =  FMA  A,  M31,  M32
//   C =  FADD B,  D

Reviewed By: jsji

Differential Revision: https://reviews.llvm.org/D80175

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineCombiner.cpp b/llvm/lib/CodeGen/MachineCombiner.cpp
index 34087d0..f241435 100644
--- a/llvm/lib/CodeGen/MachineCombiner.cpp
+++ b/llvm/lib/CodeGen/MachineCombiner.cpp
@@ -269,6 +269,8 @@ static CombinerObjective getCombinerObjective(MachineCombinerPattern P) {
   case MachineCombinerPattern::REASSOC_AX_YB:
   case MachineCombinerPattern::REASSOC_XA_BY:
   case MachineCombinerPattern::REASSOC_XA_YB:
+  case MachineCombinerPattern::REASSOC_XY_AMM_BMM:
+  case MachineCombinerPattern::REASSOC_XMM_AMM_BMM:
     return CombinerObjective::MustReduceDepth;
   default:
     return CombinerObjective::Default;