[PATCH] D102711: [GlobalOpt] Handle null check with global pointer variables

[Shimin Cui via Phabricator via llvm-commits]

scui created this revision.
scui added reviewers: vsk, efriedma, fhahn, etiotto, Whitney.
Herald added a subscriber: hiraditya.
scui requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

I'm working on extending the OptimizeGlobalAddressOfMalloc to handle some more general cases. One of the cases is the null check of global pointer variables. It is disabled with https://reviews.llvm.org/rGb7cd291c1542aee12c9e9fde6c411314a163a8ea. This PR is to reenable it while fixing the original problem reported.  The fix is to set the store value correctly when creating store for the new created global init bool symbol.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102711

Files:
  llvm/lib/Transforms/IPO/GlobalOpt.cpp
  llvm/test/Transforms/GlobalOpt/null-check-is-use-pr35760.ll


Index: llvm/test/Transforms/GlobalOpt/null-check-is-use-pr35760.ll
===================================================================
--- llvm/test/Transforms/GlobalOpt/null-check-is-use-pr35760.ll
+++ llvm/test/Transforms/GlobalOpt/null-check-is-use-pr35760.ll
@@ -3,10 +3,13 @@
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
+; CHECK: [[_ZL3G_I_INIT:@.*]] = internal unnamed_addr global i1 false
 @_ZL3g_i = internal global i32* null, align 8
 @.str = private unnamed_addr constant [2 x i8] c"0\00", align 1
 @.str.1 = private unnamed_addr constant [2 x i8] c"1\00", align 1
 
+; CHECK-LABEL: define {{.*}} @main(
+; CHECK-NEXT:    store i1 false, i1* [[_ZL3G_I_INIT]], align 1
 define dso_local i32 @main() {
   store i32* null, i32** @_ZL3g_i, align 8
   call void @_ZL13PutsSomethingv()
@@ -14,8 +17,11 @@
 }
 
 ; CHECK-LABEL: define {{.*}} @_ZL13PutsSomethingv()
-; CHECK: [[gvLoad:%.*]] = load i32*, i32** @_ZL3g_i
-; CHECK-NEXT: icmp eq i32* [[gvLoad]], null
+; CHECK-NEXT:    [[_ZL3G_I_INIT_VAL:%.*]] = load i1, i1* [[_ZL3G_I_INIT]], align 1
+; CHECK-NEXT:    [[NOTINIT:%.*]] = xor i1 [[_ZL3G_I_INIT_VAL]], true
+; CHECK-NEXT:    br i1 [[NOTINIT]], label %[[TMP1:.*]], label %[[TMP3:.*]]
+; CHECK:       [[TMP1]]:
+; CHECK-NEXT:    store i1 true, i1* [[_ZL3G_I_INIT]], align 1
 define internal void @_ZL13PutsSomethingv() {
   %1 = load i32*, i32** @_ZL3g_i, align 8
   %2 = icmp eq i32* %1, null
Index: llvm/lib/Transforms/IPO/GlobalOpt.cpp
===================================================================
--- llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -682,6 +682,8 @@
       // checked.
       if (PHIs.insert(PN).second && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
         return false;
+    } else if (isa<ICmpInst>(U) && isa<ConstantPointerNull>(U->getOperand(1))) {
+      // Ignore icmp X, null
     } else {
       //cerr << "NONTRAPPING USE: " << *U;
       return false;
@@ -923,9 +925,14 @@
   // Loop over all uses of GV, processing them in turn.
   while (!GV->use_empty()) {
     if (StoreInst *SI = dyn_cast<StoreInst>(GV->user_back())) {
-      // The global is initialized when the store to it occurs.
-      new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false,
-                    Align(1), SI->getOrdering(), SI->getSyncScopeID(), SI);
+      // The global is initialized when the store to it occurs. If the global
+      // has initial value. and the stored value is the same as the initial
+      // value, the global bool is set to false, otherwise true.
+      auto *InitBoolValue = ConstantInt::getBool(
+          GV->getContext(), !GV->hasInitializer() ||
+                                SI->getValueOperand() != GV->getInitializer());
+      new StoreInst(InitBoolValue, InitBool, false, Align(1), SI->getOrdering(),
+                    SI->getSyncScopeID(), SI);
       SI->eraseFromParent();
       continue;
     }


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D102711.346237.patch
Type: text/x-patch
Size: 3013 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20210518/adb61874/attachment.bin>