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[MemProf] Allow hint update on existing calls to nobuiltin hot/cold new #156476

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Sep 2, 2025
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[MemProf] Allow hint update on existing calls to nobuiltin hot/cold new #156476

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1 change: 1 addition & 0 deletions llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
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Original file line number Diff line number Diff line change
Expand Up @@ -189,6 +189,7 @@ class LibCallSimplifier {
Value *optimizeMemSet(CallInst *CI, IRBuilderBase &B);
Value *optimizeRealloc(CallInst *CI, IRBuilderBase &B);
Value *optimizeNew(CallInst *CI, IRBuilderBase &B, LibFunc &Func);
Value *optimizeExistingHotColdNew(CallInst *CI, IRBuilderBase &B);
Value *optimizeWcslen(CallInst *CI, IRBuilderBase &B);
Value *optimizeBCopy(CallInst *CI, IRBuilderBase &B);

Expand Down
38 changes: 36 additions & 2 deletions llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
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Expand Up @@ -1719,6 +1719,37 @@ Value *LibCallSimplifier::optimizeRealloc(CallInst *CI, IRBuilderBase &B) {
return nullptr;
}

// Allow existing calls to operator new() that takes a __hot_cold_t parameter to
// be updated with a compiler-determined hot cold hint value. This is used in
// cases where the call is marked nobuiltin (because operator new called
// explicitly) and therefore cannot be replaced with a different callee.
Comment on lines +1724 to +1725
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Do you know why the distinction of being called explicitly matters for builtin vs no-builtin?

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C++ standard: There's a reference to that here: https://clang.llvm.org/docs/LanguageExtensions.html#builtin-operator-new-and-builtin-operator-delete. I see some older conversations about this from Richard Smith.

Value *LibCallSimplifier::optimizeExistingHotColdNew(CallInst *CI,
IRBuilderBase &B) {
if (!OptimizeHotColdNew || !OptimizeExistingHotColdNew)
return nullptr;
Function *Callee = CI->getCalledFunction();
if (!Callee)
return nullptr;
LibFunc Func;
if (!TLI->getLibFunc(*Callee, Func))
return nullptr;
switch (Func) {
case LibFunc_Znwm12__hot_cold_t:
case LibFunc_ZnwmRKSt9nothrow_t12__hot_cold_t:
case LibFunc_ZnwmSt11align_val_t12__hot_cold_t:
case LibFunc_ZnwmSt11align_val_tRKSt9nothrow_t12__hot_cold_t:
case LibFunc_Znam12__hot_cold_t:
case LibFunc_ZnamRKSt9nothrow_t12__hot_cold_t:
case LibFunc_ZnamSt11align_val_t12__hot_cold_t:
case LibFunc_ZnamSt11align_val_tRKSt9nothrow_t12__hot_cold_t:
case LibFunc_size_returning_new_hot_cold:
case LibFunc_size_returning_new_aligned_hot_cold:
return optimizeNew(CI, B, Func);
default:
return nullptr;
}
}

// When enabled, replace operator new() calls marked with a hot or cold memprof
// attribute with an operator new() call that takes a __hot_cold_t parameter.
// Currently this is supported by the open source version of tcmalloc, see:
Expand Down Expand Up @@ -4094,8 +4125,11 @@ Value *LibCallSimplifier::optimizeCall(CallInst *CI, IRBuilderBase &Builder) {
// TODO: Split out the code below that operates on FP calls so that
// we can all non-FP calls with the StrictFP attribute to be
// optimized.
if (CI->isNoBuiltin())
return nullptr;
if (CI->isNoBuiltin()) {
// If this is an existing call to a hot cold operator new, we can update the
// hint parameter value, which doesn't change the callee.
return optimizeExistingHotColdNew(CI, Builder);
}

LibFunc Func;
Function *Callee = CI->getCalledFunction();
Expand Down
86 changes: 86 additions & 0 deletions llvm/test/Transforms/InstCombine/simplify-libcalls-new.ll
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Expand Up @@ -36,6 +36,10 @@ define void @new() {
; HOTCOLD: @_Znwm12__hot_cold_t(i64 10, i8 [[HOT]])
%call2 = call ptr @_Znwm(i64 10) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_Znwm(i64 10)
%call3 = call ptr @_Znwm(i64 10) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -56,6 +60,10 @@ define void @new_align() {
; HOTCOLD: @_ZnwmSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 [[HOT]])
%call2 = call ptr @_ZnwmSt11align_val_t(i64 10, i64 8) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_ZnwmSt11align_val_t(i64 10, i64 8)
%call3 = call ptr @_ZnwmSt11align_val_t(i64 10, i64 8) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -77,6 +85,10 @@ define void @new_nothrow() {
; HOTCOLD: @_ZnwmRKSt9nothrow_t12__hot_cold_t(i64 10, ptr nonnull %nt, i8 [[HOT]])
%call2 = call ptr @_ZnwmRKSt9nothrow_t(i64 10, ptr %nt) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_ZnwmRKSt9nothrow_t(i64 10, ptr nonnull %nt)
%call3 = call ptr @_ZnwmRKSt9nothrow_t(i64 10, ptr %nt) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -99,6 +111,10 @@ define void @new_align_nothrow() {
; HOTCOLD: @_ZnwmSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr nonnull %nt, i8 [[HOT]])
%call2 = call ptr @_ZnwmSt11align_val_tRKSt9nothrow_t(i64 10, i64 8, ptr %nt) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_ZnwmSt11align_val_tRKSt9nothrow_t(i64 10, i64 8, ptr nonnull %nt)
%call3 = call ptr @_ZnwmSt11align_val_tRKSt9nothrow_t(i64 10, i64 8, ptr %nt) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -118,6 +134,10 @@ define void @array_new() {
; HOTCOLD: @_Znam12__hot_cold_t(i64 10, i8 [[HOT]])
%call2 = call ptr @_Znam(i64 10) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_Znam(i64 10)
%call3 = call ptr @_Znam(i64 10) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -138,6 +158,10 @@ define void @array_new_align() {
; HOTCOLD: @_ZnamSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 [[HOT]])
%call2 = call ptr @_ZnamSt11align_val_t(i64 10, i64 8) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_ZnamSt11align_val_t(i64 10, i64 8)
%call3 = call ptr @_ZnamSt11align_val_t(i64 10, i64 8) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -159,6 +183,10 @@ define void @array_new_nothrow() {
; HOTCOLD: @_ZnamRKSt9nothrow_t12__hot_cold_t(i64 10, ptr nonnull %nt, i8 [[HOT]])
%call2 = call ptr @_ZnamRKSt9nothrow_t(i64 10, ptr %nt) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_ZnamRKSt9nothrow_t(i64 10, ptr nonnull %nt)
%call3 = call ptr @_ZnamRKSt9nothrow_t(i64 10, ptr %nt) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -181,6 +209,10 @@ define void @array_new_align_nothrow() {
; HOTCOLD: @_ZnamSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr nonnull %nt, i8 [[HOT]])
%call2 = call ptr @_ZnamSt11align_val_tRKSt9nothrow_t(i64 10, i64 8, ptr %nt) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @_ZnamSt11align_val_tRKSt9nothrow_t(i64 10, i64 8, ptr nonnull %nt)
%call3 = call ptr @_ZnamSt11align_val_tRKSt9nothrow_t(i64 10, i64 8, ptr %nt) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -200,6 +232,10 @@ define void @new_hot_cold() {
; HOTCOLD: @_Znwm12__hot_cold_t(i64 10, i8 [[PREVHINTHOT]])
%call2 = call ptr @_Znwm12__hot_cold_t(i64 10, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_Znwm12__hot_cold_t(i64 10, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_Znwm12__hot_cold_t(i64 10, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -219,6 +255,10 @@ define void @new_align_hot_cold() {
; HOTCOLD: @_ZnwmSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 [[PREVHINTHOT]])
%call2 = call ptr @_ZnwmSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_ZnwmSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_ZnwmSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -239,6 +279,10 @@ define void @new_nothrow_hot_cold() {
; HOTCOLD: @_ZnwmRKSt9nothrow_t12__hot_cold_t(i64 10, ptr nonnull %nt, i8 [[PREVHINTHOT]])
%call2 = call ptr @_ZnwmRKSt9nothrow_t12__hot_cold_t(i64 10, ptr %nt, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_ZnwmRKSt9nothrow_t12__hot_cold_t(i64 10, ptr nonnull %nt, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_ZnwmRKSt9nothrow_t12__hot_cold_t(i64 10, ptr %nt, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -259,6 +303,10 @@ define void @new_align_nothrow_hot_cold() {
; HOTCOLD: @_ZnwmSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr nonnull %nt, i8 [[PREVHINTHOT]])
%call2 = call ptr @_ZnwmSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr %nt, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_ZnwmSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr nonnull %nt, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_ZnwmSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr %nt, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -278,6 +326,10 @@ define void @array_new_hot_cold() {
; HOTCOLD: @_Znam12__hot_cold_t(i64 10, i8 [[PREVHINTHOT]])
%call2 = call ptr @_Znam12__hot_cold_t(i64 10, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_Znam12__hot_cold_t(i64 10, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_Znam12__hot_cold_t(i64 10, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -297,6 +349,10 @@ define void @array_new_align_hot_cold() {
; HOTCOLD: @_ZnamSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 [[PREVHINTHOT]])
%call2 = call ptr @_ZnamSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_ZnamSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_ZnamSt11align_val_t12__hot_cold_t(i64 10, i64 8, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -317,6 +373,10 @@ define void @array_new_nothrow_hot_cold() {
; HOTCOLD: @_ZnamRKSt9nothrow_t12__hot_cold_t(i64 10, ptr nonnull %nt, i8 [[PREVHINTHOT]])
%call2 = call ptr @_ZnamRKSt9nothrow_t12__hot_cold_t(i64 10, ptr %nt, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_ZnamRKSt9nothrow_t12__hot_cold_t(i64 10, ptr nonnull %nt, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_ZnamRKSt9nothrow_t12__hot_cold_t(i64 10, ptr %nt, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -337,6 +397,10 @@ define void @array_new_align_nothrow_hot_cold() {
; HOTCOLD: @_ZnamSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr nonnull %nt, i8 [[PREVHINTHOT]])
%call2 = call ptr @_ZnamSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr %nt, i8 7) #2
call void @dummy(ptr %call2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @_ZnamSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr nonnull %nt, i8 [[PREVHINTCOLD]])
%call3 = call ptr @_ZnamSt11align_val_tRKSt9nothrow_t12__hot_cold_t(i64 10, i64 8, ptr %nt, i8 7) #6
call void @dummy(ptr %call3)
ret void
}

Expand All @@ -359,6 +423,11 @@ define void @size_returning_test() {
%call2 = call {ptr, i64} @__size_returning_new(i64 10) #5
%p2 = extractvalue {ptr, i64} %call2, 0
call void @dummy(ptr %p2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @__size_returning_new(i64 10)
%call3 = call {ptr, i64} @__size_returning_new(i64 10) #6
%p3 = extractvalue {ptr, i64} %call3, 0
call void @dummy(ptr %p3)
ret void
}

Expand All @@ -381,6 +450,11 @@ define void @size_returning_aligned_test() {
%call2 = call {ptr, i64} @__size_returning_new_aligned(i64 10, i64 8) #5
%p2 = extractvalue {ptr, i64} %call2, 0
call void @dummy(ptr %p2)
;; Attribute cold on a nobuiltin call has no effect.
; HOTCOLD: @__size_returning_new_aligned(i64 10, i64 8)
%call3 = call {ptr, i64} @__size_returning_new_aligned(i64 10, i64 8) #6
%p3 = extractvalue {ptr, i64} %call3, 0
call void @dummy(ptr %p3)
ret void
}

Expand All @@ -403,6 +477,11 @@ define void @size_returning_update_test() {
%call2 = call {ptr, i64} @__size_returning_new_hot_cold(i64 10, i8 7) #5
%p2 = extractvalue {ptr, i64} %call2, 0
call void @dummy(ptr %p2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @__size_returning_new_hot_cold(i64 10, i8 [[PREVHINTCOLD]])
%call3 = call {ptr, i64} @__size_returning_new_hot_cold(i64 10, i8 7) #6
%p3 = extractvalue {ptr, i64} %call3, 0
call void @dummy(ptr %p3)
ret void
}

Expand All @@ -425,6 +504,11 @@ define void @size_returning_aligned_update_test() {
%call2 = call {ptr, i64} @__size_returning_new_aligned_hot_cold(i64 10, i64 8, i8 7) #5
%p2 = extractvalue {ptr, i64} %call2, 0
call void @dummy(ptr %p2)
;; Attribute cold on a nobuiltin existing hot/cold call updates the hint.
; HOTCOLD: @__size_returning_new_aligned_hot_cold(i64 10, i64 8, i8 [[PREVHINTCOLD]])
%call3 = call {ptr, i64} @__size_returning_new_aligned_hot_cold(i64 10, i64 8, i8 7) #6
%p3 = extractvalue {ptr, i64} %call3, 0
call void @dummy(ptr %p3)
ret void
}

Expand Down Expand Up @@ -463,3 +547,5 @@ attributes #2 = { builtin allocsize(0) "memprof"="hot" }
attributes #3 = { "memprof" = "cold" }
attributes #4 = { "memprof" = "notcold" }
attributes #5 = { "memprof" = "hot" }

attributes #6 = { nobuiltin allocsize(0) "memprof"="cold" }
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