[llvm] [DeadArgElim] fix verifier failure when changing musttail's function signature (PR #127366)
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Sat Feb 15 19:26:03 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: None (u4f3)
<details>
<summary>Changes</summary>
This commit is for PR107569 and PR126817.
Stop changing musttail's caller and callee's function signature when calling convention is not swifttailcc nor tailcc. Verifier makes sure musttail's caller and callee shares exactly the same signature, see commit 9ff2eb1 and PR54964 .
Otherwise just make sure the return type is the same and then process musttail like usual calls.
---
Full diff: https://github.com/llvm/llvm-project/pull/127366.diff
4 Files Affected:
- (modified) llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h (+8-5)
- (modified) llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp (+46-74)
- (modified) llvm/test/Transforms/DeadArgElim/musttail-caller.ll (+10-4)
- (added) llvm/test/Transforms/DeadArgElim/musttail-verifier.ll (+66)
``````````diff
diff --git a/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h b/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
index 63e1ad043d49f..05365b268c121 100644
--- a/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
+++ b/llvm/include/llvm/Transforms/IPO/DeadArgumentElimination.h
@@ -106,13 +106,16 @@ class DeadArgumentEliminationPass
UseMap Uses;
using LiveSet = std::set<RetOrArg>;
- using LiveFuncSet = std::set<const Function *>;
+ using FuncSet = std::set<const Function *>;
/// This set contains all values that have been determined to be live.
LiveSet LiveValues;
- /// This set contains all values that are cannot be changed in any way.
- LiveFuncSet LiveFunctions;
+ /// This set contains all functions that cannot be changed in any way.
+ FuncSet FrozenFunctions;
+
+ /// This set contains all functions that cannot change return type;
+ FuncSet FrozenRetTyFunctions;
using UseVector = SmallVector<RetOrArg, 5>;
@@ -131,12 +134,12 @@ class DeadArgumentEliminationPass
void markValue(const RetOrArg &RA, Liveness L,
const UseVector &MaybeLiveUses);
void markLive(const RetOrArg &RA);
- void markLive(const Function &F);
+ void markFrozen(const Function &F);
+ void markRetTyFrozen(const Function &F);
void propagateLiveness(const RetOrArg &RA);
bool removeDeadStuffFromFunction(Function *F);
bool deleteDeadVarargs(Function &F);
bool removeDeadArgumentsFromCallers(Function &F);
- void propagateVirtMustcallLiveness(const Module &M);
};
} // end namespace llvm
diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index ed93b4491c50e..7f53bebfab2bf 100644
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -87,11 +87,6 @@ class DAE : public ModulePass {
virtual bool shouldHackArguments() const { return false; }
};
-bool isMustTailCalleeAnalyzable(const CallBase &CB) {
- assert(CB.isMustTailCall());
- return CB.getCalledFunction() && !CB.getCalledFunction()->isDeclaration();
-}
-
} // end anonymous namespace
char DAE::ID = 0;
@@ -280,7 +275,7 @@ bool DeadArgumentEliminationPass::removeDeadArgumentsFromCallers(Function &F) {
// they are fully alive (e.g., called indirectly) and except for the fragile
// (variadic) ones. In these cases, we may still be able to improve their
// statically known call sites.
- if ((F.hasLocalLinkage() && !LiveFunctions.count(&F)) &&
+ if ((F.hasLocalLinkage() && !FrozenFunctions.count(&F)) &&
!F.getFunctionType()->isVarArg())
return false;
@@ -496,7 +491,7 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
// particular register and memory layout.
if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca) ||
F.getAttributes().hasAttrSomewhere(Attribute::Preallocated)) {
- markLive(F);
+ markFrozen(F);
return;
}
@@ -504,7 +499,7 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
// otherwise rely on the frame layout in a way that this analysis will not
// see.
if (F.hasFnAttribute(Attribute::Naked)) {
- markLive(F);
+ markFrozen(F);
return;
}
@@ -522,29 +517,25 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
// MaybeLive. Initialized to a list of RetCount empty lists.
RetUses MaybeLiveRetUses(RetCount);
- bool HasMustTailCalls = false;
for (const BasicBlock &BB : F) {
- // If we have any returns of `musttail` results - the signature can't
- // change
- if (const auto *TC = BB.getTerminatingMustTailCall()) {
- HasMustTailCalls = true;
- // In addition, if the called function is not locally defined (or unknown,
- // if this is an indirect call), we can't change the callsite and thus
- // can't change this function's signature either.
- if (!isMustTailCalleeAnalyzable(*TC)) {
- markLive(F);
+ if (BB.getTerminatingMustTailCall()) {
+ LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName()
+ << " has musttail calls\n");
+ // If the calling convention is not swifttailcc or tailcc, the caller and
+ // callee of musttail must have exactly the same signature. Otherwise we
+ // only needs to guarantee they have the same return type.
+ if (F.getCallingConv() != CallingConv::SwiftTail ||
+ F.getCallingConv() != CallingConv::Tail) {
+ markFrozen(F);
return;
+ } else {
+ markRetTyFrozen(F);
}
}
}
- if (HasMustTailCalls) {
- LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName()
- << " has musttail calls\n");
- }
-
if (!F.hasLocalLinkage() && (!ShouldHackArguments || F.isIntrinsic())) {
- markLive(F);
+ markFrozen(F);
return;
}
@@ -555,8 +546,6 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
// of them turn out to be live.
unsigned NumLiveRetVals = 0;
- bool HasMustTailCallers = false;
-
// Loop all uses of the function.
for (const Use &U : F.uses()) {
// If the function is PASSED IN as an argument, its address has been
@@ -564,14 +553,24 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
const auto *CB = dyn_cast<CallBase>(U.getUser());
if (!CB || !CB->isCallee(&U) ||
CB->getFunctionType() != F.getFunctionType()) {
- markLive(F);
+ markFrozen(F);
return;
}
- // The number of arguments for `musttail` call must match the number of
- // arguments of the caller
- if (CB->isMustTailCall())
- HasMustTailCallers = true;
+ if (CB->isMustTailCall()) {
+ LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName()
+ << " has musttail callers\n");
+ // If the calling convention is not swifttailcc or tailcc, the caller and
+ // callee of musttail must have exactly the same signature. Otherwise we
+ // only needs to guarantee they have the same return type.
+ if (F.getCallingConv() != CallingConv::SwiftTail ||
+ F.getCallingConv() != CallingConv::Tail) {
+ markFrozen(F);
+ return;
+ } else {
+ markRetTyFrozen(F);
+ }
+ }
// If we end up here, we are looking at a direct call to our function.
@@ -610,11 +609,6 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
}
}
- if (HasMustTailCallers) {
- LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - " << F.getName()
- << " has musttail callers\n");
- }
-
// Now we've inspected all callers, record the liveness of our return values.
for (unsigned Ri = 0; Ri != RetCount; ++Ri)
markValue(createRet(&F, Ri), RetValLiveness[Ri], MaybeLiveRetUses[Ri]);
@@ -628,19 +622,12 @@ void DeadArgumentEliminationPass::surveyFunction(const Function &F) {
for (Function::const_arg_iterator AI = F.arg_begin(), E = F.arg_end();
AI != E; ++AI, ++ArgI) {
Liveness Result;
- if (F.getFunctionType()->isVarArg() || HasMustTailCallers ||
- HasMustTailCalls) {
+ if (F.getFunctionType()->isVarArg()) {
// Variadic functions will already have a va_arg function expanded inside
// them, making them potentially very sensitive to ABI changes resulting
// from removing arguments entirely, so don't. For example AArch64 handles
// register and stack HFAs very differently, and this is reflected in the
// IR which has already been generated.
- //
- // `musttail` calls to this function restrict argument removal attempts.
- // The signature of the caller must match the signature of the function.
- //
- // `musttail` calls in this function prevents us from changing its
- // signature
Result = Live;
} else {
// See what the effect of this use is (recording any uses that cause
@@ -683,11 +670,11 @@ void DeadArgumentEliminationPass::markValue(const RetOrArg &RA, Liveness L,
/// Mark the given Function as alive, meaning that it cannot be changed in any
/// way. Additionally, mark any values that are used as this function's
/// parameters or by its return values (according to Uses) live as well.
-void DeadArgumentEliminationPass::markLive(const Function &F) {
- LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Intrinsically live fn: "
+void DeadArgumentEliminationPass::markFrozen(const Function &F) {
+ LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - frozen fn: "
<< F.getName() << "\n");
- // Mark the function as live.
- LiveFunctions.insert(&F);
+ // Mark the function as frozen.
+ FrozenFunctions.insert(&F);
// Mark all arguments as live.
for (unsigned ArgI = 0, E = F.arg_size(); ArgI != E; ++ArgI)
propagateLiveness(createArg(&F, ArgI));
@@ -696,6 +683,12 @@ void DeadArgumentEliminationPass::markLive(const Function &F) {
propagateLiveness(createRet(&F, Ri));
}
+void DeadArgumentEliminationPass::markRetTyFrozen(const Function &F) {
+ LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - frozen return type fn: "
+ << F.getName() << "\n");
+ FrozenRetTyFunctions.insert(&F);
+}
+
/// Mark the given return value or argument as live. Additionally, mark any
/// values that are used by this value (according to Uses) live as well.
void DeadArgumentEliminationPass::markLive(const RetOrArg &RA) {
@@ -710,7 +703,7 @@ void DeadArgumentEliminationPass::markLive(const RetOrArg &RA) {
}
bool DeadArgumentEliminationPass::isLive(const RetOrArg &RA) {
- return LiveFunctions.count(RA.F) || LiveValues.count(RA);
+ return FrozenFunctions.count(RA.F) || LiveValues.count(RA);
}
/// Given that RA is a live value, propagate it's liveness to any other values
@@ -734,8 +727,8 @@ void DeadArgumentEliminationPass::propagateLiveness(const RetOrArg &RA) {
/// Transform the function and all the callees of the function to not have these
/// arguments and return values.
bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
- // Don't modify fully live functions
- if (LiveFunctions.count(F))
+ // Don't modify frozen functions
+ if (FrozenFunctions.count(F))
return false;
// Start by computing a new prototype for the function, which is the same as
@@ -807,7 +800,8 @@ bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
// performance win, so the second option can just be used always for now.
//
// This should be revisited if 'returned' is ever applied more liberally.
- if (RetTy->isVoidTy() || HasLiveReturnedArg) {
+ if (RetTy->isVoidTy() || HasLiveReturnedArg ||
+ FrozenRetTyFunctions.count(F)) {
NRetTy = RetTy;
} else {
// Look at each of the original return values individually.
@@ -1109,26 +1103,6 @@ bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
return true;
}
-void DeadArgumentEliminationPass::propagateVirtMustcallLiveness(
- const Module &M) {
- // If a function was marked "live", and it has musttail callers, they in turn
- // can't change either.
- LiveFuncSet NewLiveFuncs(LiveFunctions);
- while (!NewLiveFuncs.empty()) {
- LiveFuncSet Temp;
- for (const auto *F : NewLiveFuncs)
- for (const auto *U : F->users())
- if (const auto *CB = dyn_cast<CallBase>(U))
- if (CB->isMustTailCall())
- if (!LiveFunctions.count(CB->getParent()->getParent()))
- Temp.insert(CB->getParent()->getParent());
- NewLiveFuncs.clear();
- NewLiveFuncs.insert(Temp.begin(), Temp.end());
- for (const auto *F : Temp)
- markLive(*F);
- }
-}
-
PreservedAnalyses DeadArgumentEliminationPass::run(Module &M,
ModuleAnalysisManager &) {
bool Changed = false;
@@ -1149,8 +1123,6 @@ PreservedAnalyses DeadArgumentEliminationPass::run(Module &M,
for (auto &F : M)
surveyFunction(F);
- propagateVirtMustcallLiveness(M);
-
// Now, remove all dead arguments and return values from each function in
// turn. We use make_early_inc_range here because functions will probably get
// removed (i.e. replaced by new ones).
diff --git a/llvm/test/Transforms/DeadArgElim/musttail-caller.ll b/llvm/test/Transforms/DeadArgElim/musttail-caller.ll
index 4549ab41fb8ad..01666a5f9ad04 100644
--- a/llvm/test/Transforms/DeadArgElim/musttail-caller.ll
+++ b/llvm/test/Transforms/DeadArgElim/musttail-caller.ll
@@ -1,16 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -passes=deadargelim -S < %s | FileCheck %s
; PR36441
; Dead arguments should not be removed in presence of `musttail` calls.
-; CHECK-LABEL: define internal void @test(i32 %a, i32 %b)
-; CHECK: musttail call void @foo(i32 %a, i32 0)
-; FIXME: we should replace those with `undef`s
define internal void @test(i32 %a, i32 %b) {
+; CHECK-LABEL: define internal void @test(
+; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT: musttail call void @foo(i32 poison, i32 poison)
+; CHECK-NEXT: ret void
+;
musttail call void @foo(i32 %a, i32 0)
ret void
}
-; CHECK-LABEL: define internal void @foo(i32 %a, i32 %b)
define internal void @foo(i32 %a, i32 %b) {
+; CHECK-LABEL: define internal void @foo(
+; CHECK-SAME: i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT: ret void
+;
ret void
}
diff --git a/llvm/test/Transforms/DeadArgElim/musttail-verifier.ll b/llvm/test/Transforms/DeadArgElim/musttail-verifier.ll
new file mode 100644
index 0000000000000..b1be1328940ed
--- /dev/null
+++ b/llvm/test/Transforms/DeadArgElim/musttail-verifier.ll
@@ -0,0 +1,66 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; Testcases comes from PR126817 and PR107569
+; See PR54964 and langref for more information about how llvm deal with musttail currently
+; RUN: opt -passes=deadargelim -S < %s | FileCheck %s
+
+define i64 @A() {
+; CHECK-LABEL: define i64 @A() {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[V2660:%.*]] = musttail call i64 @B()
+; CHECK-NEXT: ret i64 [[V2660]]
+;
+entry:
+ %v2660 = musttail call i64 @B()
+ ret i64 %v2660
+}
+
+define internal i64 @B() {
+; CHECK-LABEL: define internal i64 @B() {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: ret i64 0
+;
+entry:
+ ret i64 0
+}
+
+define internal i64 @C() {
+; CHECK-LABEL: define internal i64 @C() {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[V30543:%.*]] = musttail call i64 @B()
+; CHECK-NEXT: ret i64 [[V30543]]
+;
+entry:
+ %v30543 = musttail call i64 @B()
+ ret i64 %v30543
+}
+
+%struct.S = type { double }
+
+define internal %struct.S @F38() {
+; CHECK-LABEL: define internal %struct.S @F38() {
+; CHECK-NEXT: ret [[STRUCT_S:%.*]] zeroinitializer
+;
+ ret %struct.S { double 0.0 }
+}
+
+define internal %struct.S @F36() {
+; CHECK-LABEL: define internal %struct.S @F36() {
+; CHECK-NEXT: [[TMP1:%.*]] = alloca [[STRUCT_S:%.*]], align 8
+; CHECK-NEXT: [[TMP2:%.*]] = musttail call [[STRUCT_S]] @[[F38:[a-zA-Z0-9_$\"\\.-]*[a-zA-Z_$\"\\.-][a-zA-Z0-9_$\"\\.-]*]]()
+; CHECK-NEXT: ret [[STRUCT_S]] [[TMP2]]
+;
+ %1 = alloca %struct.S, align 8
+ %3 = musttail call %struct.S @F38()
+ ret %struct.S %3
+}
+
+define double @foo() {
+; CHECK-LABEL: define double @foo() {
+; CHECK-NEXT: [[TMP1:%.*]] = call [[STRUCT_S:%.*]] @[[F36:[a-zA-Z0-9_$\"\\.-]*[a-zA-Z_$\"\\.-][a-zA-Z0-9_$\"\\.-]*]]()
+; CHECK-NEXT: [[TMP2:%.*]] = extractvalue [[STRUCT_S]] [[TMP1]], 0
+; CHECK-NEXT: ret double [[TMP2]]
+;
+ %3 = call %struct.S @F36()
+ %5 = extractvalue %struct.S %3, 0
+ ret double %5
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/127366
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