<div dir="ltr">I'm relatively certain that the test is bad wrt the C++ standard. The compiler is allowed to elide new even if it is user-defined. The standard's escape hatch is calling "::operator new(size)" instead of using a new expression. Building with -fno-builtin should also work. Or feed the pointer into an __asm__ barrier to prevent the compiler from removing it.</div><br><br><div class="gmail_quote"><div dir="ltr">On Wed, Feb 21, 2018 at 2:49 AM Sam Clegg <<a href="mailto:sbc@google.com">sbc@google.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">We have some test code on the WebAssembly waterfall the broke as a<br>
result of this. Perhaps the test is bad but I've distilled to the<br>
following:<br>
<br>
```<br>
#include <stdio.h><br>
#include <stdlib.h><br>
<br>
void* operator new(size_t s) {<br>
static int n = 1;<br>
printf("new %zu\n", s);<br>
return &n;<br>
}<br>
<br>
int main() {<br>
int* foo = new int;<br>
printf("%p\n", foo);<br>
return 0;<br>
}<br>
```<br>
<br>
Before this change the above program will always print "new ...".<br>
After this change it only prints this O0. In O1 and O2 the call to<br>
new is elided. Is this intended?<br>
<br>
On Tue, Feb 20, 2018 at 2:00 PM, Benjamin Kramer via llvm-commits<br>
<<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>> wrote:<br>
> Author: d0k<br>
> Date: Tue Feb 20 14:00:33 2018<br>
> New Revision: 325630<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=325630&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=325630&view=rev</a><br>
> Log:<br>
> [MemoryBuiltins] Check nobuiltin status when identifying calls to free.<br>
><br>
> This is usually not a problem because this code's main purpose is<br>
> eliminating unused new/delete pairs. We got deletes of nullptr or<br>
> nobuiltin deletes of builtin new wrong though.<br>
><br>
> Modified:<br>
> llvm/trunk/lib/Analysis/MemoryBuiltins.cpp<br>
> llvm/trunk/test/Transforms/InstCombine/malloc-free-delete.ll<br>
><br>
> Modified: llvm/trunk/lib/Analysis/MemoryBuiltins.cpp<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=325630&r1=325629&r2=325630&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=325630&r1=325629&r2=325630&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/lib/Analysis/MemoryBuiltins.cpp (original)<br>
> +++ llvm/trunk/lib/Analysis/MemoryBuiltins.cpp Tue Feb 20 14:00:33 2018<br>
> @@ -112,10 +112,9 @@ static const Function *getCalledFunction<br>
><br>
> IsNoBuiltin = CS.isNoBuiltin();<br>
><br>
> - const Function *Callee = CS.getCalledFunction();<br>
> - if (!Callee || !Callee->isDeclaration())<br>
> - return nullptr;<br>
> - return Callee;<br>
> + if (const Function *Callee = CS.getCalledFunction())<br>
> + return Callee;<br>
> + return nullptr;<br>
> }<br>
><br>
> /// Returns the allocation data for the given value if it's either a call to a<br>
> @@ -350,11 +349,10 @@ const CallInst *llvm::extractCallocCall(<br>
><br>
> /// isFreeCall - Returns non-null if the value is a call to the builtin free()<br>
> const CallInst *llvm::isFreeCall(const Value *I, const TargetLibraryInfo *TLI) {<br>
> - const CallInst *CI = dyn_cast<CallInst>(I);<br>
> - if (!CI || isa<IntrinsicInst>(CI))<br>
> - return nullptr;<br>
> - Function *Callee = CI->getCalledFunction();<br>
> - if (Callee == nullptr)<br>
> + bool IsNoBuiltinCall;<br>
> + const Function *Callee =<br>
> + getCalledFunction(I, /*LookThroughBitCast=*/false, IsNoBuiltinCall);<br>
> + if (Callee == nullptr || IsNoBuiltinCall)<br>
> return nullptr;<br>
><br>
> StringRef FnName = Callee->getName();<br>
> @@ -400,7 +398,7 @@ const CallInst *llvm::isFreeCall(const V<br>
> if (FTy->getParamType(0) != Type::getInt8PtrTy(Callee->getContext()))<br>
> return nullptr;<br>
><br>
> - return CI;<br>
> + return dyn_cast<CallInst>(I);<br>
> }<br>
><br>
> //===----------------------------------------------------------------------===//<br>
><br>
> Modified: llvm/trunk/test/Transforms/InstCombine/malloc-free-delete.ll<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/malloc-free-delete.ll?rev=325630&r1=325629&r2=325630&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/malloc-free-delete.ll?rev=325630&r1=325629&r2=325630&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/test/Transforms/InstCombine/malloc-free-delete.ll (original)<br>
> +++ llvm/trunk/test/Transforms/InstCombine/malloc-free-delete.ll Tue Feb 20 14:00:33 2018<br>
> @@ -146,7 +146,11 @@ lpad.i:<br>
> }<br>
><br>
> declare i8* @_Znwm(i64) nobuiltin<br>
> -declare i8* @_Znwj(i32) nobuiltin<br>
> +define i8* @_Znwj(i32 %n) nobuiltin {<br>
> + %z = zext i32 %n to i64<br>
> + call i8* @_Znwm(i64 %z)<br>
> + ret i8* %m<br>
> +}<br>
> declare i8* @_Znam(i64) nobuiltin<br>
> declare i8* @_Znaj(i32) nobuiltin<br>
> declare void @_ZdlPv(i8*) nobuiltin<br>
> @@ -197,3 +201,19 @@ define void @test9() {<br>
> call void @"\01??3@YAXPEAX@Z"(i8* %new_long_long) builtin<br>
> ret void<br>
> }<br>
> +<br>
> +define void @test10() {<br>
> +; CHECK-LABEL: @test10<br>
> +; CHECK: call void @_ZdlPv<br>
> + call void @_ZdlPv(i8* null)<br>
> + ret void<br>
> +}<br>
> +<br>
> +define void @test11() {<br>
> +; CHECK-LABEL: @test11<br>
> +; CHECK: call i8* @_Znwm<br>
> +; CHECK: call void @_ZdlPv<br>
> + %call = call i8* @_Znwm(i64 8) builtin<br>
> + call void @_ZdlPv(i8* %call)<br>
> + ret void<br>
> +}<br>
><br>
><br>
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</blockquote></div>