[InstCombine] Simplify nonnull phi nodes (#128466)

Fix some regressions caused by
#128111.
Compile-time impact:
https://llvm-compile-time-tracker.com/compare.php?from=1e0e4169dd00bf8a37cef8d74d0add7861982c4e&to=3a27268e264826ef9cf493f645507e490f05e7f3&stat=instructions%3Au

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp

@@ -1011,6 +1011,21 @@ Value *InstCombinerImpl::simplifyNonNullOperand(Value *V,
     }
   }
 
+  if (auto *PHI = dyn_cast<PHINode>(V)) {
+    bool Changed = false;
+    for (Use &U : PHI->incoming_values()) {
+      // We set Depth to RecursionLimit to avoid expensive recursion.
+      if (auto *Res = simplifyNonNullOperand(U.get(), HasDereferenceable,
+                                             RecursionLimit)) {
+        replaceUse(U, Res);
+        Changed = true;
+      }
+    }
+    if (Changed)
+      addToWorklist(PHI);
+    return nullptr;
+  }
+
   return nullptr;
 }
 

llvm/test/Transforms/InstCombine/load.ll

@@ -481,3 +481,30 @@ define i16 @load_select_with_null_gep3(i1 %cond, ptr %p, i64 %x, i64 %y) {
   %res = load i16, ptr %gep2, align 2
   ret i16 %res
 }
+
+define i32 @test_load_phi_with_select(ptr %p, i1 %cond1) {
+; CHECK-LABEL: @test_load_phi_with_select(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP_BODY:%.*]]
+; CHECK:       loop.body:
+; CHECK-NEXT:    [[TARGET:%.*]] = getelementptr inbounds nuw i8, ptr [[BASE:%.*]], i64 24
+; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[TARGET]], align 4
+; CHECK-NEXT:    [[COND21:%.*]] = icmp eq i32 [[LOAD]], 0
+; CHECK-NEXT:    br i1 [[COND21]], label [[LOOP_BODY]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[LOAD]]
+;
+entry:
+  br label %loop.body
+
+loop.body:
+  %base = phi ptr [ %p, %entry ], [ %sel, %loop.body ]
+  %target = getelementptr inbounds i8, ptr %base, i64 24
+  %load = load i32, ptr %target, align 4
+  %sel = select i1 %cond1, ptr null, ptr %p
+  %cond2 = icmp eq i32 %load, 0
+  br i1 %cond2, label %loop.body, label %exit
+
+exit:
+  ret i32 %load
+}