[SCCP][FuncSpec] Poison unreachable constant global variable user (#155753)
Fixes #155738.
The original assumption "we already replaced its users with a constant"
for the global variable becomes incorrect after #154668. The users in
the dead function are not simplified, in fact.
This patch poisons all the unsimplified constant global variable users.
diff --git a/llvm/lib/Transforms/IPO/SCCP.cpp b/llvm/lib/Transforms/IPO/SCCP.cpp
index e98a70f..f4961fa 100644
--- a/llvm/lib/Transforms/IPO/SCCP.cpp
+++ b/llvm/lib/Transforms/IPO/SCCP.cpp
@@ -330,12 +330,15 @@
LLVM_DEBUG(dbgs() << "Found that GV '" << GV->getName()
<< "' is constant!\n");
for (User *U : make_early_inc_range(GV->users())) {
- // We can remove LoadInst here, because we already replaced its users
- // with a constant.
+ // We can remove LoadInst here. The LoadInsts in dead functions marked by
+ // FuncSpec are not simplified to constants, thus poison them.
assert((isa<StoreInst>(U) || isa<LoadInst>(U)) &&
"Only Store|Load Instruction can be user of GlobalVariable at "
"reaching here.");
- cast<Instruction>(U)->eraseFromParent();
+ Instruction *I = cast<Instruction>(U);
+ if (isa<LoadInst>(I))
+ I->replaceAllUsesWith(PoisonValue::get(I->getType()));
+ I->eraseFromParent();
}
// Try to create a debug constant expression for the global variable
diff --git a/llvm/test/Transforms/FunctionSpecialization/dead-gv-load.ll b/llvm/test/Transforms/FunctionSpecialization/dead-gv-load.ll
new file mode 100644
index 0000000..134a79d
--- /dev/null
+++ b/llvm/test/Transforms/FunctionSpecialization/dead-gv-load.ll
@@ -0,0 +1,31 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=ipsccp --funcspec-min-function-size=1 -S < %s | FileCheck %s
+
+@gv = internal global ptr null
+
+define i8 @caller() {
+; CHECK-LABEL: define i8 @caller() {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[CALL1:%.*]] = call i8 @callee.specialized.1(i32 1)
+; CHECK-NEXT: [[CALL2:%.*]] = call i8 @callee.specialized.2(i32 0)
+; CHECK-NEXT: ret i8 undef
+;
+entry:
+ %call1 = call i8 @callee(i32 1)
+ %call2 = call i8 @callee(i32 0)
+ ret i8 %call2
+}
+
+define internal i8 @callee(i32 %arg) {
+entry:
+ %useless = icmp ne i32 %arg, 0
+ br label %loop
+
+loop: ; preds = %loop, %entry
+ br label %loop
+
+dead_bb: ; No predecessors!
+ %l1 = load ptr, ptr @gv, align 8
+ %l2 = load ptr, ptr %l1, align 8
+ ret i8 0
+}
