[llvm] [FunctionAttrs] Don't bail out on unknown calls (PR #150958)
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Mon Jul 28 07:26:34 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
When inferring attributes, we should not bail out early on unknown calls (such as virtual calls), as we may still have call-site attributes that can be used for inference.
This drops the HasUnknownCall flag and adjusts the norecurse implementation to check call attributes (all other inference already did that).
Fixes https://github.com/llvm/llvm-project/issues/150817.
---
Full diff: https://github.com/llvm/llvm-project/pull/150958.diff
5 Files Affected:
- (modified) llvm/lib/Transforms/IPO/FunctionAttrs.cpp (+11-31)
- (modified) llvm/test/Transforms/FunctionAttrs/noalias.ll (+1-1)
- (modified) llvm/test/Transforms/FunctionAttrs/nonnull.ll (+1-1)
- (modified) llvm/test/Transforms/FunctionAttrs/norecurse.ll (+3-2)
- (modified) llvm/test/Transforms/FunctionAttrs/nounwind.ll (+3-2)
``````````diff
diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index f43202eea6306..7fde4605e5686 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -1863,7 +1863,6 @@ void AttributeInferer::run(const SCCNodeSet &SCCNodes,
struct SCCNodesResult {
SCCNodeSet SCCNodes;
- bool HasUnknownCall;
};
} // end anonymous namespace
@@ -2087,11 +2086,13 @@ static void addNoRecurseAttrs(const SCCNodeSet &SCCNodes,
for (auto &BB : *F)
for (auto &I : BB.instructionsWithoutDebug())
if (auto *CB = dyn_cast<CallBase>(&I)) {
+ if (CB->hasFnAttr(Attribute::NoRecurse))
+ continue;
+
Function *Callee = CB->getCalledFunction();
if (!Callee || Callee == F ||
- (!Callee->doesNotRecurse() &&
- !(Callee->isDeclaration() &&
- Callee->hasFnAttribute(Attribute::NoCallback))))
+ !(Callee->isDeclaration() &&
+ Callee->hasFnAttribute(Attribute::NoCallback)))
// Function calls a potentially recursive function.
return;
}
@@ -2227,29 +2228,13 @@ static void addWillReturn(const SCCNodeSet &SCCNodes,
static SCCNodesResult createSCCNodeSet(ArrayRef<Function *> Functions) {
SCCNodesResult Res;
- Res.HasUnknownCall = false;
for (Function *F : Functions) {
if (!F || F->hasOptNone() || F->hasFnAttribute(Attribute::Naked) ||
F->isPresplitCoroutine()) {
- // Treat any function we're trying not to optimize as if it were an
- // indirect call and omit it from the node set used below.
- Res.HasUnknownCall = true;
+ // Omit any functions we're trying not to optimize from the set.
continue;
}
- // Track whether any functions in this SCC have an unknown call edge.
- // Note: if this is ever a performance hit, we can common it with
- // subsequent routines which also do scans over the instructions of the
- // function.
- if (!Res.HasUnknownCall) {
- for (Instruction &I : instructions(*F)) {
- if (auto *CB = dyn_cast<CallBase>(&I)) {
- if (!CB->getCalledFunction()) {
- Res.HasUnknownCall = true;
- break;
- }
- }
- }
- }
+
Res.SCCNodes.insert(F);
}
return Res;
@@ -2282,15 +2267,10 @@ deriveAttrsInPostOrder(ArrayRef<Function *> Functions, AARGetterT &&AARGetter,
addColdAttrs(Nodes.SCCNodes, Changed);
addWillReturn(Nodes.SCCNodes, Changed);
addNoUndefAttrs(Nodes.SCCNodes, Changed);
-
- // If we have no external nodes participating in the SCC, we can deduce some
- // more precise attributes as well.
- if (!Nodes.HasUnknownCall) {
- addNoAliasAttrs(Nodes.SCCNodes, Changed);
- addNonNullAttrs(Nodes.SCCNodes, Changed);
- inferAttrsFromFunctionBodies(Nodes.SCCNodes, Changed);
- addNoRecurseAttrs(Nodes.SCCNodes, Changed);
- }
+ addNoAliasAttrs(Nodes.SCCNodes, Changed);
+ addNonNullAttrs(Nodes.SCCNodes, Changed);
+ inferAttrsFromFunctionBodies(Nodes.SCCNodes, Changed);
+ addNoRecurseAttrs(Nodes.SCCNodes, Changed);
// Finally, infer the maximal set of attributes from the ones we've inferred
// above. This is handling the cases where one attribute on a signature
diff --git a/llvm/test/Transforms/FunctionAttrs/noalias.ll b/llvm/test/Transforms/FunctionAttrs/noalias.ll
index 8beb6fe78f852..de8bd9eade621 100644
--- a/llvm/test/Transforms/FunctionAttrs/noalias.ll
+++ b/llvm/test/Transforms/FunctionAttrs/noalias.ll
@@ -235,7 +235,7 @@ define ptr @return_unknown_call(ptr %fn) {
}
define ptr @return_unknown_noalias_call(ptr %fn) {
-; CHECK-LABEL: define ptr @return_unknown_noalias_call(
+; CHECK-LABEL: define noalias ptr @return_unknown_noalias_call(
; CHECK-SAME: ptr readonly captures(none) [[FN:%.*]]) {
; CHECK-NEXT: [[A:%.*]] = call noalias ptr [[FN]]()
; CHECK-NEXT: ret ptr [[A]]
diff --git a/llvm/test/Transforms/FunctionAttrs/nonnull.ll b/llvm/test/Transforms/FunctionAttrs/nonnull.ll
index 9b17ded3bdb26..8df242fb023af 100644
--- a/llvm/test/Transforms/FunctionAttrs/nonnull.ll
+++ b/llvm/test/Transforms/FunctionAttrs/nonnull.ll
@@ -1412,7 +1412,7 @@ define ptr @unknown_func(ptr %fn) {
}
define ptr @unknown_nonnull_func(ptr %fn) {
-; FNATTRS-LABEL: define ptr @unknown_nonnull_func(
+; FNATTRS-LABEL: define nonnull ptr @unknown_nonnull_func(
; FNATTRS-SAME: ptr readonly captures(none) [[FN:%.*]]) {
; FNATTRS-NEXT: [[RES:%.*]] = call nonnull ptr [[FN]]()
; FNATTRS-NEXT: ret ptr [[RES]]
diff --git a/llvm/test/Transforms/FunctionAttrs/norecurse.ll b/llvm/test/Transforms/FunctionAttrs/norecurse.ll
index 5cb8ac05847aa..a9437848150da 100644
--- a/llvm/test/Transforms/FunctionAttrs/norecurse.ll
+++ b/llvm/test/Transforms/FunctionAttrs/norecurse.ll
@@ -258,9 +258,10 @@ define void @unknown_call(ptr %fn) {
}
define void @unknown_norecurse_call(ptr %fn) {
+; FNATTRS: Function Attrs: norecurse
; FNATTRS-LABEL: define {{[^@]+}}@unknown_norecurse_call
-; FNATTRS-SAME: (ptr readonly captures(none) [[FN:%.*]]) {
-; FNATTRS-NEXT: call void [[FN]]() #[[ATTR7:[0-9]+]]
+; FNATTRS-SAME: (ptr readonly captures(none) [[FN:%.*]]) #[[ATTR7:[0-9]+]] {
+; FNATTRS-NEXT: call void [[FN]]() #[[ATTR7]]
; FNATTRS-NEXT: ret void
;
; ATTRIBUTOR-LABEL: define {{[^@]+}}@unknown_norecurse_call
diff --git a/llvm/test/Transforms/FunctionAttrs/nounwind.ll b/llvm/test/Transforms/FunctionAttrs/nounwind.ll
index a64d9a6504256..076a7df2781ce 100644
--- a/llvm/test/Transforms/FunctionAttrs/nounwind.ll
+++ b/llvm/test/Transforms/FunctionAttrs/nounwind.ll
@@ -418,9 +418,10 @@ define void @unknown_call(ptr %fn) {
}
define void @unknown_nounwind_call(ptr %fn) {
+; FNATTRS: Function Attrs: nounwind
; FNATTRS-LABEL: define {{[^@]+}}@unknown_nounwind_call
-; FNATTRS-SAME: (ptr readonly captures(none) [[FN:%.*]]) {
-; FNATTRS-NEXT: call void [[FN]]() #[[ATTR2:[0-9]+]]
+; FNATTRS-SAME: (ptr readonly captures(none) [[FN:%.*]]) #[[ATTR2:[0-9]+]] {
+; FNATTRS-NEXT: call void [[FN]]() #[[ATTR2]]
; FNATTRS-NEXT: ret void
;
; ATTRIBUTOR: Function Attrs: nounwind
``````````
</details>
https://github.com/llvm/llvm-project/pull/150958
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