[llvm] r239849 - Reapply 239795 - [InstCombine] Propagate non-null facts to call parameters
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 25 16:54:51 PDT 2015
Pete,
I'm not really following why your example is problematic, even for an
non-zero address space. We're not changing anything about the
interpretation of the null pointer with this change. We're simply
propagating that the pointer *isn't* null, whatever meaning that might
have for the given address space. What I am missing in your
explanation? Where does this go wrong?
Are you possibly trying to say that we false concluded it was nonnull at
the call site? i.e. Did you find a bug in isKnownNonNull for non-zero
address space pointers?
Philip
On 08/25/2015 11:09 AM, Pete Cooper wrote:
> Hey Philip
>
> We just came across a case internally where this optimization applied not null to a pointer with an address space other than 0.
>
> Sorry, I reviewed this and really should have thought about that at the time.
>
> What are your thoughts on this? I believe we can only assume nullness on address space 0 and have to leave all others alone.
>
> I don’t think we have an optimization pipeline which will expose this, but lets assume that we have something like:
>
> foo(&g)
> ...
> foo(int *addresspace(1) p) {
> if (p != null) { bar(); }
> }
>
> then you could imagine us propagating the not null from the call to the callee (if all calls to the callee have not null), and so we have
>
> foo(&g __attribute__((not null)) )
> ...
> foo(int *addresspace(1) __attribute__((not null)) p) {
> if (p != null) { bar(); }
> }
>
> and then some optimization would constant fold the if to give us
>
> foo(int *addresspace(1) __attribute__((not null)) p) {
> bar();
> }
>
> which might be incorrect if 0 was a valid address on address space 1.
>
> Cheers,
> Pete
>> On Jun 16, 2015, at 1:24 PM, Philip Reames <listmail at philipreames.com> wrote:
>>
>> Author: reames
>> Date: Tue Jun 16 15:24:25 2015
>> New Revision: 239849
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=239849&view=rev
>> Log:
>> Reapply 239795 - [InstCombine] Propagate non-null facts to call parameters
>>
>> The original change broke clang side tests. I will be submitting those momentarily. This change includes post commit feedback on the original change from from Pete Cooper.
>>
>> Original Submission comments:
>> If a parameter to a function is known non-null, use the existing parameter attributes to record that fact at the call site. This has no optimization benefit by itself - that I know of - but is an enabling change for http://reviews.llvm.org/D9129.
>>
>> Differential Revision: http://reviews.llvm.org/D9132
>>
>>
>> Modified:
>> llvm/trunk/include/llvm/IR/CallSite.h
>> llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
>> llvm/trunk/test/CodeGen/NVPTX/intrin-nocapture.ll
>> llvm/trunk/test/Transforms/Inline/byval-tail-call.ll
>> llvm/trunk/test/Transforms/InstCombine/select.ll
>>
>> Modified: llvm/trunk/include/llvm/IR/CallSite.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/CallSite.h?rev=239849&r1=239848&r2=239849&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/IR/CallSite.h (original)
>> +++ llvm/trunk/include/llvm/IR/CallSite.h Tue Jun 16 15:24:25 2015
>> @@ -27,6 +27,7 @@
>> #define LLVM_IR_CALLSITE_H
>>
>> #include "llvm/ADT/PointerIntPair.h"
>> +#include "llvm/ADT/iterator_range.h"
>> #include "llvm/IR/Attributes.h"
>> #include "llvm/IR/CallingConv.h"
>> #include "llvm/IR/Instructions.h"
>> @@ -150,6 +151,9 @@ public:
>> }
>>
>> IterTy arg_end() const { return (*this)->op_end() - getArgumentEndOffset(); }
>> + iterator_range<IterTy> args() const {
>> + return iterator_range<IterTy>(arg_begin(), arg_end());
>> + }
>> bool arg_empty() const { return arg_end() == arg_begin(); }
>> unsigned arg_size() const { return unsigned(arg_end() - arg_begin()); }
>>
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=239849&r1=239848&r2=239849&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Tue Jun 16 15:24:25 2015
>> @@ -1391,11 +1391,29 @@ static IntrinsicInst *FindInitTrampoline
>> // visitCallSite - Improvements for call and invoke instructions.
>> //
>> Instruction *InstCombiner::visitCallSite(CallSite CS) {
>> +
>> if (isAllocLikeFn(CS.getInstruction(), TLI))
>> return visitAllocSite(*CS.getInstruction());
>>
>> bool Changed = false;
>>
>> + // Mark any parameters that are known to be non-null with the nonnull
>> + // attribute. This is helpful for inlining calls to functions with null
>> + // checks on their arguments.
>> + unsigned ArgNo = 0;
>> + for (Value *V : CS.args()) {
>> + if (!CS.paramHasAttr(ArgNo+1, Attribute::NonNull) &&
>> + isKnownNonNull(V)) {
>> + AttributeSet AS = CS.getAttributes();
>> + AS = AS.addAttribute(CS.getInstruction()->getContext(), ArgNo+1,
>> + Attribute::NonNull);
>> + CS.setAttributes(AS);
>> + Changed = true;
>> + }
>> + ArgNo++;
>> + }
>> + assert(ArgNo == CS.arg_size() && "sanity check");
>> +
>> // If the callee is a pointer to a function, attempt to move any casts to the
>> // arguments of the call/invoke.
>> Value *Callee = CS.getCalledValue();
>>
>> Modified: llvm/trunk/test/CodeGen/NVPTX/intrin-nocapture.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/NVPTX/intrin-nocapture.ll?rev=239849&r1=239848&r2=239849&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/CodeGen/NVPTX/intrin-nocapture.ll (original)
>> +++ llvm/trunk/test/CodeGen/NVPTX/intrin-nocapture.ll Tue Jun 16 15:24:25 2015
>> @@ -11,7 +11,7 @@ declare i32 addrspace(1)* @llvm.nvvm.ptr
>> ; CHECK: @bar
>> define void @bar() {
>> %t1 = alloca i32
>> -; CHECK: call i32 addrspace(1)* @llvm.nvvm.ptr.gen.to.global.p1i32.p0i32(i32* %t1)
>> +; CHECK: call i32 addrspace(1)* @llvm.nvvm.ptr.gen.to.global.p1i32.p0i32(i32* nonnull %t1)
>> ; CHECK-NEXT: store i32 10, i32* %t1
>> %t2 = call i32 addrspace(1)* @llvm.nvvm.ptr.gen.to.global.p1i32.p0i32(i32* %t1)
>> store i32 10, i32* %t1
>>
>> Modified: llvm/trunk/test/Transforms/Inline/byval-tail-call.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Inline/byval-tail-call.ll?rev=239849&r1=239848&r2=239849&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/Inline/byval-tail-call.ll (original)
>> +++ llvm/trunk/test/Transforms/Inline/byval-tail-call.ll Tue Jun 16 15:24:25 2015
>> @@ -33,7 +33,7 @@ define void @frob(i32* %x) {
>> ; CHECK: %[[POS:.*]] = alloca i32
>> ; CHECK: %[[VAL:.*]] = load i32, i32* %x
>> ; CHECK: store i32 %[[VAL]], i32* %[[POS]]
>> -; CHECK: {{^ *}}call void @ext(i32* %[[POS]]
>> +; CHECK: {{^ *}}call void @ext(i32* nonnull %[[POS]]
>> ; CHECK: tail call void @ext(i32* null)
>> ; CHECK: ret void
>> tail call void @qux(i32* byval %x)
>>
>> Modified: llvm/trunk/test/Transforms/InstCombine/select.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select.ll?rev=239849&r1=239848&r2=239849&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/InstCombine/select.ll (original)
>> +++ llvm/trunk/test/Transforms/InstCombine/select.ll Tue Jun 16 15:24:25 2015
>> @@ -1265,7 +1265,7 @@ define i32 @test77(i1 %flag, i32* %x) {
>> ; load does.
>> ; CHECK-LABEL: @test77(
>> ; CHECK: %[[A:.*]] = alloca i32, align 1
>> -; CHECK: call void @scribble_on_i32(i32* %[[A]])
>> +; CHECK: call void @scribble_on_i32(i32* nonnull %[[A]])
>> ; CHECK: store i32 0, i32* %x
>> ; CHECK: %[[P:.*]] = select i1 %flag, i32* %[[A]], i32* %x
>> ; CHECK: load i32, i32* %[[P]]
>>
>>
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