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[GlobalOpt] Check if users are CallBase when changing CC #161399

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Merged
merged 3 commits into from
Oct 1, 2025
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[GlobalOpt] Check if users are CallBase when changing CC #161399

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421dbff
autogenerate tests
XChy Sep 30, 2025
6baf27d
[GlobalOpt] Check if users are CallBase when changing CC
XChy Sep 30, 2025
05b250a
check called operand
XChy Oct 1, 2025
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16 changes: 11 additions & 5 deletions llvm/lib/Transforms/IPO/GlobalOpt.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1680,7 +1680,9 @@ processGlobal(GlobalValue &GV,
/// FastCC.
static void ChangeCalleesToFastCall(Function *F) {
for (User *U : F->users())
cast<CallBase>(U)->setCallingConv(CallingConv::Fast);
if (auto *Call = dyn_cast<CallBase>(U))
if (Call->getCalledOperand() == F)
Call->setCallingConv(CallingConv::Fast);
}

static AttributeList StripAttr(LLVMContext &C, AttributeList Attrs,
Expand Down Expand Up @@ -1766,10 +1768,12 @@ isValidCandidateForColdCC(Function &F,
return false;

for (User *U : F.users()) {
CallBase &CB = cast<CallBase>(*U);
Function *CallerFunc = CB.getParent()->getParent();
CallBase *CB = dyn_cast<CallBase>(U);
if (!CB || CB->getCalledOperand() != &F)
continue;
Function *CallerFunc = CB->getParent()->getParent();
BlockFrequencyInfo &CallerBFI = GetBFI(*CallerFunc);
if (!isColdCallSite(CB, CallerBFI))
if (!isColdCallSite(*CB, CallerBFI))
return false;
if (!llvm::is_contained(AllCallsCold, CallerFunc))
return false;
Expand All @@ -1779,7 +1783,9 @@ isValidCandidateForColdCC(Function &F,

static void changeCallSitesToColdCC(Function *F) {
for (User *U : F->users())
cast<CallBase>(U)->setCallingConv(CallingConv::Cold);
if (auto *Call = dyn_cast<CallBase>(U))
if (Call->getCalledOperand() == F)
Call->setCallingConv(CallingConv::Cold);
}

// This function iterates over all the call instructions in the input Function
Expand Down
90 changes: 74 additions & 16 deletions llvm/test/Transforms/GlobalOpt/fastcc.ll
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@@ -1,58 +1,106 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
; RUN: opt < %s -passes=globalopt -S | FileCheck %s

declare token @llvm.call.preallocated.setup(i32)
declare ptr @llvm.call.preallocated.arg(token, i32)

define internal i32 @f(ptr %m) {
; CHECK-LABEL: define internal fastcc i32 @f
; CHECK-LABEL: define internal fastcc i32 @f(
; CHECK-SAME: ptr [[M:%.*]]) unnamed_addr {
; CHECK-NEXT: [[V:%.*]] = load i32, ptr [[M]], align 4
; CHECK-NEXT: ret i32 [[V]]
;
%v = load i32, ptr %m
ret i32 %v
}

define internal x86_thiscallcc i32 @g(ptr %m) {
; CHECK-LABEL: define internal fastcc i32 @g
; CHECK-LABEL: define internal fastcc i32 @g(
; CHECK-SAME: ptr [[M:%.*]]) unnamed_addr {
; CHECK-NEXT: [[V:%.*]] = load i32, ptr [[M]], align 4
; CHECK-NEXT: ret i32 [[V]]
;
%v = load i32, ptr %m
ret i32 %v
}

; Leave this one alone, because the user went out of their way to request this
; convention.
define internal coldcc i32 @h(ptr %m) {
; CHECK-LABEL: define internal coldcc i32 @h
; CHECK-LABEL: define internal coldcc i32 @h(
; CHECK-SAME: ptr [[M:%.*]]) unnamed_addr {
; CHECK-NEXT: [[V:%.*]] = load i32, ptr [[M]], align 4
; CHECK-NEXT: ret i32 [[V]]
;
%v = load i32, ptr %m
ret i32 %v
}

define internal i32 @j(ptr %m) {
; CHECK-LABEL: define internal i32 @j
; CHECK-LABEL: define internal i32 @j(
; CHECK-SAME: ptr [[M:%.*]]) {
; CHECK-NEXT: [[V:%.*]] = load i32, ptr [[M]], align 4
; CHECK-NEXT: ret i32 [[V]]
;
%v = load i32, ptr %m
ret i32 %v
}

define internal i32 @inalloca(ptr inalloca(i32) %p) {
; CHECK-LABEL: define internal fastcc i32 @inalloca(ptr %p)
; CHECK-LABEL: define internal fastcc i32 @inalloca(
; CHECK-SAME: ptr [[P:%.*]]) unnamed_addr {
; CHECK-NEXT: [[RV:%.*]] = load i32, ptr [[P]], align 4
; CHECK-NEXT: ret i32 [[RV]]
;
%rv = load i32, ptr %p
ret i32 %rv
}

define i32 @inalloca2_caller(ptr inalloca(i32) %p) {
; CHECK-LABEL: define i32 @inalloca2_caller(
; CHECK-SAME: ptr inalloca(i32) [[P:%.*]]) local_unnamed_addr {
; CHECK-NEXT: [[RV:%.*]] = musttail call i32 @inalloca2(ptr inalloca(i32) [[P]])
; CHECK-NEXT: ret i32 [[RV]]
;
%rv = musttail call i32 @inalloca2(ptr inalloca(i32) %p)
ret i32 %rv
}
define internal i32 @inalloca2(ptr inalloca(i32) %p) {
; Because of the musttail caller, this inalloca cannot be dropped.
; CHECK-LABEL: define internal i32 @inalloca2(ptr inalloca(i32) %p)
; CHECK-LABEL: define internal i32 @inalloca2(
; CHECK-SAME: ptr inalloca(i32) [[P:%.*]]) unnamed_addr {
; CHECK-NEXT: [[RV:%.*]] = load i32, ptr [[P]], align 4
; CHECK-NEXT: ret i32 [[RV]]
;
%rv = load i32, ptr %p
ret i32 %rv
}

define internal i32 @preallocated(ptr preallocated(i32) %p) {
; CHECK-LABEL: define internal fastcc i32 @preallocated(ptr %p)
; CHECK-LABEL: define internal fastcc i32 @preallocated(
; CHECK-SAME: ptr [[P:%.*]]) unnamed_addr {
; CHECK-NEXT: [[RV:%.*]] = load i32, ptr [[P]], align 4
; CHECK-NEXT: ret i32 [[RV]]
;
%rv = load i32, ptr %p
ret i32 %rv
}

define void @call_things() {
; CHECK-LABEL: define void @call_things() local_unnamed_addr {
; CHECK-NEXT: [[M:%.*]] = alloca i32, align 4
; CHECK-NEXT: [[TMP1:%.*]] = call fastcc i32 @f(ptr [[M]])
; CHECK-NEXT: [[TMP2:%.*]] = call fastcc i32 @g(ptr [[M]])
; CHECK-NEXT: [[TMP3:%.*]] = call coldcc i32 @h(ptr [[M]])
; CHECK-NEXT: [[TMP4:%.*]] = call i32 @j(ptr [[M]])
; CHECK-NEXT: [[ARGS:%.*]] = alloca inalloca i32, align 4
; CHECK-NEXT: [[TMP5:%.*]] = call fastcc i32 @inalloca(ptr [[ARGS]])
; CHECK-NEXT: [[TMP6:%.*]] = call ptr @llvm.stacksave.p0()
; CHECK-NEXT: [[PAARG:%.*]] = alloca i32, align 4
; CHECK-NEXT: [[TMP7:%.*]] = call fastcc i32 @preallocated(ptr [[PAARG]])
; CHECK-NEXT: call void @llvm.stackrestore.p0(ptr [[TMP6]])
; CHECK-NEXT: ret void
;
%m = alloca i32
call i32 @f(ptr %m)
call x86_thiscallcc i32 @g(ptr %m)
Expand All @@ -65,15 +113,25 @@ define void @call_things() {
call i32 @preallocated(ptr preallocated(i32) %N) ["preallocated"(token %c)]
ret void
}
; CHECK-LABEL: define void @call_things()
; CHECK: call fastcc i32 @f
; CHECK: call fastcc i32 @g
; CHECK: call coldcc i32 @h
; CHECK: call i32 @j
; CHECK: call fastcc i32 @inalloca(ptr %args)
; CHECK-NOT: llvm.call.preallocated
; CHECK: call fastcc i32 @preallocated(ptr %paarg)

@llvm.used = appending global [1 x ptr] [
ptr @j
ptr @j
], section "llvm.metadata"

define internal i32 @assume_fastcc() {
; CHECK-LABEL: define internal fastcc i32 @assume_fastcc() {
; CHECK-NEXT: [[OBJSIZE:%.*]] = call i32 @llvm.objectsize.i32.p0(ptr @assume_fastcc, i1 false, i1 false, i1 false)
; CHECK-NEXT: ret i32 [[OBJSIZE]]
;
%objsize = call i32 @llvm.objectsize.i32.p0(ptr @assume_fastcc, i1 false, i1 false, i1 false)
ret i32 %objsize
}

define internal i32 @constexpr_self_user() addrspace(1) {
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Remove the address space, assuming it's not relevant somehow?

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It's only reproducible with addrspacecast. See also https://godbolt.org/z/qcfY8z91G.
My description is not clear. Actually, hasChangeableCCImpl ignores assume-like calls with addrspacecast.
But we try to cast addrspacecast to CallBase later.

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Ah, but that indicates another issue now. We'll also ignore assume-like calls directly:

llvm-project/llvm/lib/IR/Function.cpp

Lines 995 to 999 in 3c0f7b1

if (IgnoreAssumeLikeCalls) {
if (const auto *I = dyn_cast<IntrinsicInst>(Call))
if (I->isAssumeLikeIntrinsic())
continue;
}

But in that case we're going to change the CC on the assume-like call, not on a call to the function. So I think the code needs to check that it's the callee operand.

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Thanks, I missed it. Fix it now.

; CHECK-LABEL: define internal fastcc i32 @constexpr_self_user() addrspace(1) {
; CHECK-NEXT: [[OBJSIZE:%.*]] = call i32 @llvm.objectsize.i32.p0(ptr addrspacecast (ptr addrspace(1) @constexpr_self_user to ptr), i1 false, i1 false, i1 false)
; CHECK-NEXT: ret i32 [[OBJSIZE]]
;
%objsize = call i32 @llvm.objectsize.i32.p0(ptr addrspacecast (ptr addrspace(1) @constexpr_self_user to ptr), i1 false, i1 false, i1 false)
ret i32 %objsize
}