recalculate the live interval of the defined register of xvmaddmdp in the VSX FMA mutation pass. (llvm#116071)

The patch fix llvm#116061

The root cause of the assertion is that the FMA mutation pass does not
update the subranges of the live interval for the defined register of
the modified instruction .

it recalculate the live interval of the defined register of xvmaddmdp in
the VSX FMA mutation pass.

Author: diggerlin

llvm/lib/Target/PowerPC/PPCVSXFMAMutate.cpp

@@ -288,21 +288,11 @@ namespace {
           UseMO.substVirtReg(KilledProdReg, KilledProdSubReg, *TRI);
         }
 
-        // Extend the live intervals of the killed product operand to hold the
-        // fma result.
+        // Recalculate the live intervals of the killed product operand.
+        LIS->removeInterval(KilledProdReg);
+        LiveInterval &NewFMAInt =
+            LIS->createAndComputeVirtRegInterval(KilledProdReg);
 
-        LiveInterval &NewFMAInt = LIS->getInterval(KilledProdReg);
-        for (auto &AI : FMAInt) {
-          // Don't add the segment that corresponds to the original copy.
-          if (AI.valno == AddendValNo)
-            continue;
-
-          VNInfo *NewFMAValNo =
-              NewFMAInt.getNextValue(AI.start, LIS->getVNInfoAllocator());
-
-          NewFMAInt.addSegment(
-              LiveInterval::Segment(AI.start, AI.end, NewFMAValNo));
-        }
         LLVM_DEBUG(dbgs() << "  extended: " << NewFMAInt << '\n');
 
         // Extend the live interval of the addend source (it might end at the

llvm/test/CodeGen/PowerPC/pr116071.ll

@@ -0,0 +1,26 @@
+; RUN: llc -disable-ppc-vsx-fma-mutation=false -mcpu=pwr10 -verify-machineinstrs \
+; RUN:   -ppc-asm-full-reg-names -mtriple powerpc64-ibm-aix7.2.0.0 < %s | FileCheck %s 
+
+target datalayout = "E-m:a-Fi64-i64:64-n32:64-S128-v256:256:256-v512:512:512"
+
+define void @initial(<2 x double> %0){
+entry:
+  %1 = fmul <2 x double> %0, zeroinitializer
+  br label %for.cond251.preheader.lr.ph
+
+for.cond251.preheader.lr.ph:                      ; preds = %for.cond251.preheader.lr.ph, %entry
+  %2 = phi double [ %3, %for.cond251.preheader.lr.ph ], [ 0.000000e+00, %entry ]
+  %3 = phi double [ %7, %for.cond251.preheader.lr.ph ], [ 0.000000e+00, %entry ]
+  %add737 = fadd double %3, %2
+  %4 = insertelement <2 x double> zeroinitializer, double %add737, i64 0
+  %5 = fmul contract <2 x double> %4, zeroinitializer
+  %6 = fadd contract <2 x double> %1, %5
+  %7 = extractelement <2 x double> %6, i64 0
+  br label %for.cond251.preheader.lr.ph
+}
+
+; CHECK:        xsadddp f4, f3, f4
+; CHECK-NEXT:   xxmrghd vs5, vs4, vs2
+; CHECK-NEXT:   fmr f4, f3
+; CHECK-NEXT:   xvmaddmdp vs5, vs0, vs1
+; CHECK-NEXT:   fmr f3, f5