[PowerPC] hoist xxspltiw instruction out of the loop with FMA mutation pass. (#111696)

Summary: 
   
The patch fixes the issue [[PowerPC] missing VSX FMA Mutation optimize
in some case for option -schedule-ppc-vsx-fma-mutation-early
#111906](https://github.com/llvm/llvm-project/issues/111906)
   
In certain cases, the Register Coalescer pass—which eliminates COPY
instructions—can interfere with the PowerPC VSX FMA Mutation pass.
Specifically, it can prevent the mutation of a COPY adjacent to an
XSMADDADP into a single XSMADDMDP instruction. As a result, the xxspltiw
instruction is not hoisted out of the loop as expected, leading to
missed optimization opportunities.

To address this, the patch ensures that the `VSX FMA Mutation` pass runs
before the `Register Coalescer` pass when the
-schedule-ppc-vsx-fma-mutation-early option is enabled.

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp b/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
index ff600d7..359a43d 100644
--- a/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
+++ b/llvm/lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -559,7 +559,8 @@ void PPCPassConfig::addMachineSSAOptimization() {
 
 void PPCPassConfig::addPreRegAlloc() {
   if (getOptLevel() != CodeGenOptLevel::None) {
-    insertPass(VSXFMAMutateEarly ? &RegisterCoalescerID : &MachineSchedulerID,
+    insertPass(VSXFMAMutateEarly ? &TwoAddressInstructionPassID
+                                 : &MachineSchedulerID,
                &PPCVSXFMAMutateID);
   }