[InstCombine]PtrReplacer: Correctly handle select with unavailable operands

The testcase I added previously failed because a SelectInst with invalid operands was created (one side `addrspace(4)`, the other `addrspace(5)`).
PointerReplacer needs to dig deeper if the true and/or false instructions of the select are not available.

Fixes SWDEV-542957

Author: Pierre-vh

llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -277,6 +277,15 @@ bool PointerReplacer::collectUsers() {
           Worklist.emplace_back(I);
   };
 
+  auto TryPushInstOperand = [&](Instruction *InstOp) {
+    if (!UsersToReplace.contains(InstOp)) {
+      if (!ValuesToRevisit.insert(InstOp))
+        return false;
+      Worklist.emplace_back(InstOp);
+    }
+    return true;
+  };
+
   PushUsersToWorklist(&Root);
   while (!Worklist.empty()) {
     Instruction *Inst = Worklist.pop_back_val();
@@ -309,21 +318,26 @@ bool PointerReplacer::collectUsers() {
       // incoming values.
       Worklist.emplace_back(PHI);
       for (unsigned Idx = 0; Idx < PHI->getNumIncomingValues(); ++Idx) {
-        auto *IncomingValue = cast<Instruction>(PHI->getIncomingValue(Idx));
-        if (UsersToReplace.contains(IncomingValue))
-          continue;
-        if (!ValuesToRevisit.insert(IncomingValue))
+        if (!TryPushInstOperand(cast<Instruction>(PHI->getIncomingValue(Idx))))
           return false;
-        Worklist.emplace_back(IncomingValue);
       }
     } else if (auto *SI = dyn_cast<SelectInst>(Inst)) {
       auto *TrueInst = dyn_cast<Instruction>(SI->getTrueValue());
       auto *FalseInst = dyn_cast<Instruction>(SI->getFalseValue());
       if (!TrueInst || !FalseInst)
         return false;
 
-      UsersToReplace.insert(SI);
-      PushUsersToWorklist(SI);
+      if (isAvailable(TrueInst) && isAvailable(FalseInst)) {
+        UsersToReplace.insert(SI);
+        PushUsersToWorklist(SI);
+        continue;
+      }
+
+      // Push select back onto the stack, followed by unavailable true/false
+      // value.
+      Worklist.emplace_back(SI);
+      if (!TryPushInstOperand(TrueInst) || !TryPushInstOperand(FalseInst))
+        return false;
     } else if (auto *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
       UsersToReplace.insert(GEP);
       PushUsersToWorklist(GEP);

llvm/test/Transforms/InstCombine/AMDGPU/ptr-replacer-select-addrspacecast-crash.ll

@@ -0,0 +1,20 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -passes=instcombine %s -S -o - | FileCheck %s
+
+; Crashed in IC PtrReplacer because an invalid select was generated with addrspace(4) and addrspace(5)
+; operands.
+
+define amdgpu_kernel void @eggs(ptr addrspace(4) byref([12 x i8]) align 16 %arg) {
+; CHECK-LABEL: define amdgpu_kernel void @eggs(
+; CHECK-SAME: ptr addrspace(4) byref([12 x i8]) align 16 [[ARG:%.*]]) {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    ret void
+;
+bb:
+  %alloca = alloca i32, i32 0, align 8, addrspace(5)
+  %alloca1 = alloca [12 x i8], align 16, addrspace(5)
+  call void @llvm.memcpy.p5.p4.i64(ptr addrspace(5) %alloca1, ptr addrspace(4) %arg, i64 0, i1 false)
+  %select = select i1 false, ptr addrspace(5) %alloca1, ptr addrspace(5) %alloca
+  call void @llvm.memcpy.p0.p5.i64(ptr null, ptr addrspace(5) %select, i64 0, i1 false)
+  ret void
+}