Fixed generation of unnecessary phi-node in gvn pre for getelementptr…

… (cherry-pick from upstream with stripPointerCasts added)

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -2188,7 +2188,7 @@ bool GVN::performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
 }
 
 bool GVN::performScalarPRE(Instruction *CurInst) {
-  if (isa<AllocaInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
+  if (isa<AllocaInst>(CurInst) || CurInst->isTerminator() ||
       isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() ||
       CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
       isa<DbgInfoIntrinsic>(CurInst))
@@ -2201,10 +2201,24 @@ bool GVN::performScalarPRE(Instruction *CurInst) {
   if (isa<CmpInst>(CurInst))
     return false;
 
-  // We don't currently value number ANY inline asm calls.
-  if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
-    if (CallI->isInlineAsm())
+  // Don't do PRE on GEPs. The inserted PHI would prevent CodeGenPrepare from
+  // sinking the addressing mode computation back to its uses. Extending the
+  // GEP's live range increases the register pressure, and therefore it can
+  // introduce unnecessary spills.
+  //
+  // This doesn't prevent Load PRE. PHI translation will make the GEP available
+  // to the load by moving it to the predecessor block if necessary.
+  if (isa<GetElementPtrInst>(CurInst->stripPointerCasts()))
+    return false;
+
+  if (auto *CallB = dyn_cast<CallInst>(CurInst)) {
+    // We don't currently value number ANY inline asm calls.
+    if (CallB->isInlineAsm())
       return false;
+    // Don't do PRE on convergent calls.
+    if (CallB->isConvergent())
+      return false;
+  }
 
   uint32_t ValNo = VN.lookup(CurInst);