[llvm] r344558 - [hot-cold-split] fix static analysis of cold regions
Lang Hames via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 15 15:31:54 PDT 2018
Hi Sebastian,
I have changed the TermianatorInst* to an Instruction* in r344566 to get
the tree building again.
I think this is the right fix, but wanted to double check with you.
Cheers,
Lang.
On Mon, Oct 15, 2018 at 3:14 PM Lang Hames <lhames at gmail.com> wrote:
> Looks like this might be incompatible with Chandler's change in r344504.
> On Top-of-tree I am seeing:
>
> /path/to/llvm/lib/Transforms/IPO/HotColdSplitting.cpp:153:25: error:
> cannot initialize a variable of type 'const llvm::TerminatorInst *' with an
> rvalue of type 'const llvm::Instruction *'
> const TerminatorInst *I = BB.getTerminator();
>
> Cheers,
> Lang.
>
>
>
>
> On Mon, Oct 15, 2018 at 2:45 PM Sebastian Pop via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: spop
>> Date: Mon Oct 15 14:43:11 2018
>> New Revision: 344558
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=344558&view=rev
>> Log:
>> [hot-cold-split] fix static analysis of cold regions
>>
>> Make the code of blockEndsInUnreachable to match the function
>> blockEndsInUnreachable in CodeGen/BranchFolding.cpp. I also have
>> added a note to make sure the code of this function will not be
>> modified unless the back-end version is also modified.
>>
>> An early return before outlining has been added to avoid
>> outlining the full function body when the first block in the
>> function is marked cold.
>>
>> The static analysis of cold code has been amended to avoid
>> marking the whole function as cold by back-propagation
>> because the back-propagation would mark blocks with return
>> statements as cold.
>>
>> The patch adds debug statements to help discover these problems.
>>
>> Differential Revision: https://reviews.llvm.org/D52904
>>
>> Modified:
>> llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp
>> llvm/trunk/test/Transforms/HotColdSplit/split-cold-1.ll
>> llvm/trunk/test/Transforms/HotColdSplit/split-cold-2.ll
>>
>> Modified: llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp?rev=344558&r1=344557&r2=344558&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp (original)
>> +++ llvm/trunk/lib/Transforms/IPO/HotColdSplitting.cpp Mon Oct 15
>> 14:43:11 2018
>> @@ -101,14 +101,19 @@ static bool isSingleEntrySingleExit(Basi
>> return true;
>> }
>>
>> +// Same as blockEndsInUnreachable in CodeGen/BranchFolding.cpp. Do not
>> modify
>> +// this function unless you modify the MBB version as well.
>> +//
>> +/// A no successor, non-return block probably ends in unreachable and is
>> cold.
>> +/// Also consider a block that ends in an indirect branch to be a return
>> block,
>> +/// since many targets use plain indirect branches to return.
>> bool blockEndsInUnreachable(const BasicBlock &BB) {
>> + if (!succ_empty(&BB))
>> + return false;
>> if (BB.empty())
>> return true;
>> const Instruction *I = BB.getTerminator();
>> - if (isa<ReturnInst>(I) || isa<IndirectBrInst>(I))
>> - return true;
>> - // Unreachable blocks do not have any successor.
>> - return succ_empty(&BB);
>> + return !(isa<ReturnInst>(I) || isa<IndirectBrInst>(I));
>> }
>>
>> static bool exceptionHandlingFunctions(const CallInst *CI) {
>> @@ -123,8 +128,7 @@ static bool exceptionHandlingFunctions(c
>> FName == "__cxa_end_catch";
>> }
>>
>> -static
>> -bool unlikelyExecuted(const BasicBlock &BB) {
>> +static bool unlikelyExecuted(const BasicBlock &BB) {
>> if (blockEndsInUnreachable(BB))
>> return true;
>> // Exception handling blocks are unlikely executed.
>> @@ -145,13 +149,32 @@ bool unlikelyExecuted(const BasicBlock &
>> return false;
>> }
>>
>> +static bool returnsOrHasSideEffects(const BasicBlock &BB) {
>> + const TerminatorInst *I = BB.getTerminator();
>> + if (isa<ReturnInst>(I) || isa<IndirectBrInst>(I) || isa<InvokeInst>(I))
>> + return true;
>> +
>> + for (const Instruction &I : BB)
>> + if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
>> + if (CI->hasFnAttr(Attribute::NoReturn))
>> + return true;
>> +
>> + if (isa<InlineAsm>(CI->getCalledValue()))
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> static DenseSetBB getHotBlocks(Function &F) {
>>
>> // Mark all cold basic blocks.
>> DenseSetBB ColdBlocks;
>> for (BasicBlock &BB : F)
>> - if (unlikelyExecuted(BB))
>> + if (unlikelyExecuted(BB)) {
>> + LLVM_DEBUG(llvm::dbgs() << "\nForward propagation marks cold: " <<
>> BB);
>> ColdBlocks.insert((const BasicBlock *)&BB);
>> + }
>>
>> // Forward propagation: basic blocks are hot when they are reachable
>> from the
>> // beginning of the function through a path that does not contain cold
>> blocks.
>> @@ -203,7 +226,12 @@ static DenseSetBB getHotBlocks(Function
>> if (ColdBlocks.count(It))
>> continue;
>>
>> + // Do not back-propagate to blocks that return or have side effects.
>> + if (returnsOrHasSideEffects(*It))
>> + continue;
>> +
>> // Move the block from HotBlocks to ColdBlocks.
>> + LLVM_DEBUG(llvm::dbgs() << "\nBack propagation marks cold: " << *It);
>> HotBlocks.erase(It);
>> ColdBlocks.insert(It);
>>
>> @@ -353,6 +381,12 @@ const Function *HotColdSplitting::outlin
>> // Walking the dominator tree allows us to find the largest
>> // cold region.
>> BasicBlock *Begin = DT->getRootNode()->getBlock();
>> +
>> + // Early return if the beginning of the function has been marked cold,
>> + // otherwise all the function gets outlined.
>> + if (PSI->isColdBB(Begin, BFI) || !HotBlocks.count(Begin))
>> + return nullptr;
>> +
>> for (auto I = df_begin(Begin), E = df_end(Begin); I != E; ++I) {
>> BasicBlock *BB = *I;
>> if (PSI->isColdBB(BB, BFI) || !HotBlocks.count(BB)) {
>>
>> Modified: llvm/trunk/test/Transforms/HotColdSplit/split-cold-1.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/HotColdSplit/split-cold-1.ll?rev=344558&r1=344557&r2=344558&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/HotColdSplit/split-cold-1.ll (original)
>> +++ llvm/trunk/test/Transforms/HotColdSplit/split-cold-1.ll Mon Oct 15
>> 14:43:11 2018
>> @@ -1,9 +1,11 @@
>> ; RUN: opt -hotcoldsplit -S < %s | FileCheck %s
>> ; RUN: opt -passes=hotcoldsplit -S < %s | FileCheck %s
>>
>> -; Outlined function is called from a basic block named codeRepl
>> -; CHECK: codeRepl:
>> -; CHECK-NEXT: call void @foo
>> +; Check that the function is not split. Outlined function is called from
>> a
>> +; basic block named codeRepl.
>> +
>> +; CHECK-LABEL: @foo
>> +; CHECK-NOT: codeRepl
>> define void @foo() {
>> entry:
>> br i1 undef, label %if.then, label %if.end
>> @@ -23,3 +25,19 @@ cleanup40:
>> return: ; preds = %cleanup40
>> ret void
>> }
>> +
>> +; Check that the function is not split. We used to outline the full
>> function.
>> +
>> +; CHECK-LABEL: @fun
>> +; CHECK-NOT: codeRepl
>> +
>> +define void @fun() {
>> +entry:
>> + br i1 undef, label %if.then, label %if.end
>> +
>> +if.then: ; preds = %entry
>> + br label %if.end
>> +
>> +if.end: ; preds = %entry
>> + ret void
>> +}
>>
>> Modified: llvm/trunk/test/Transforms/HotColdSplit/split-cold-2.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/HotColdSplit/split-cold-2.ll?rev=344558&r1=344557&r2=344558&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/HotColdSplit/split-cold-2.ll (original)
>> +++ llvm/trunk/test/Transforms/HotColdSplit/split-cold-2.ll Mon Oct 15
>> 14:43:11 2018
>> @@ -4,6 +4,10 @@
>> ; Make sure this compiles. This test used to fail with an invalid phi
>> node: the
>> ; two predecessors were outlined and the SSA representation was invalid.
>>
>> +; CHECK-LABEL: @fun
>> +; CHECK: codeRepl:
>> +; CHECK-NEXT: call void @fun_if.else
>> +
>> define void @fun() {
>> entry:
>> br i1 undef, label %if.then, label %if.else
>>
>>
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>> llvm-commits at lists.llvm.org
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>>
>
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