1 files changed, 9 insertions, 2 deletions
diff --git a/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp b/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp
index 0bd2bd84db0..6b19a2f7118 100644
--- a/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp
+++ b/llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp
@@ -220,6 +220,14 @@ protected:
         if (OldFMAReg == KilledProdReg)
           continue;
 
+        // If there isn't a class that fits, we can't perform the transform.
+        // This is needed for correctness with a mixture of VSX and Altivec
+        // instructions to make sure that a low VSX register is not assigned to
+        // the Altivec instruction.
+        if (!MRI.constrainRegClass(KilledProdReg,
+                                   MRI.getRegClass(OldFMAReg)))
+          continue;
+
         assert(OldFMAReg == AddendMI->getOperand(0).getReg() &&
                "Addend copy not tied to old FMA output!");
 
@@ -262,8 +270,7 @@ protected:
           if (UseMI == AddendMI)
             continue;
 
-          UseMO.setReg(KilledProdReg);
-          UseMO.setSubReg(KilledProdSubReg);
+          UseMO.substVirtReg(KilledProdReg, KilledProdSubReg, *TRI);
         }
 
         // Extend the live intervals of the killed product operand to hold the