<div dir="ltr"><br><br><div class="gmail_quote"><div dir="ltr">On Tue, Mar 20, 2018 at 10:11 AM Philip Reames via llvm-commits <<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: reames<br>
Date: Tue Mar 20 10:09:21 2018<br>
New Revision: 328004<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=328004&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=328004&view=rev</a><br>
Log:<br>
Add an analysis printer for must execute reasoning<br>
<br>
Many of our loop passes make use of so called "must execute" or "guaranteed to execute" facts to prove the legality of code motion. The basic notion is that we know (by assumption) an instruction didn't fault at it's original location, so if the location we move it to is strictly post dominated by the original, then we can't have introduced a new fault.<br>
<br>
At the moment, the testing for this logic is somewhat adhoc and done mostly through LICM. Since I'm working on that code, I want to improve the testing. This patch is the first step in that direction. It doesn't actually test the variant used by the loop passes - I need to move that to the Analysis library first - but instead exercises an alternate implementation used by SCEV. (I plan on merging both implementations.)<br>
<br>
Note: I'll be replacing the printing logic within this with an annotation based version in the near future. Anna suggested this in review, and it seems like a strictly better format.<br>
<br>
Differential Revision: <a href="https://reviews.llvm.org/D44524" rel="noreferrer" target="_blank">https://reviews.llvm.org/D44524</a><br>
<br>
<br>
Added:<br>
llvm/trunk/lib/Analysis/MustExecute.cpp<br>
llvm/trunk/test/Analysis/MustExecute/<br>
llvm/trunk/test/Analysis/MustExecute/loop-header.ll<br>
Modified:<br>
llvm/trunk/include/llvm/Analysis/Passes.h<br>
llvm/trunk/include/llvm/InitializePasses.h<br>
llvm/trunk/include/llvm/LinkAllPasses.h<br>
llvm/trunk/lib/Analysis/Analysis.cpp<br>
llvm/trunk/lib/Analysis/CMakeLists.txt<br>
<br>
Modified: llvm/trunk/include/llvm/Analysis/Passes.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/Passes.h?rev=328004&r1=328003&r2=328004&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/Passes.h?rev=328004&r1=328003&r2=328004&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/include/llvm/Analysis/Passes.h (original)<br>
+++ llvm/trunk/include/llvm/Analysis/Passes.h Tue Mar 20 10:09:21 2018<br>
@@ -96,6 +96,14 @@ namespace llvm {<br>
//<br>
FunctionPass *createMemDerefPrinter();<br>
<br>
+ //===--------------------------------------------------------------------===//<br>
+ //<br>
+ // createMustExecutePrinter - This pass collects information about which<br>
+ // instructions within a loop are guaranteed to execute if the loop header is<br>
+ // entered and prints it with -analyze.<br>
+ //<br>
+ FunctionPass *createMustExecutePrinter();<br>
+<br>
}<br>
<br>
#endif<br>
<br>
Modified: llvm/trunk/include/llvm/InitializePasses.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=328004&r1=328003&r2=328004&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/InitializePasses.h?rev=328004&r1=328003&r2=328004&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/include/llvm/InitializePasses.h (original)<br>
+++ llvm/trunk/include/llvm/InitializePasses.h Tue Mar 20 10:09:21 2018<br>
@@ -268,6 +268,7 @@ void initializeMergedLoadStoreMotionLega<br>
void initializeMetaRenamerPass(PassRegistry&);<br>
void initializeModuleDebugInfoPrinterPass(PassRegistry&);<br>
void initializeModuleSummaryIndexWrapperPassPass(PassRegistry&);<br>
+void initializeMustExecutePrinterPass(PassRegistry&);<br>
void initializeNameAnonGlobalLegacyPassPass(PassRegistry&);<br>
void initializeNaryReassociateLegacyPassPass(PassRegistry&);<br>
void initializeNewGVNLegacyPassPass(PassRegistry&);<br>
<br>
Modified: llvm/trunk/include/llvm/LinkAllPasses.h<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=328004&r1=328003&r2=328004&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/LinkAllPasses.h?rev=328004&r1=328003&r2=328004&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/include/llvm/LinkAllPasses.h (original)<br>
+++ llvm/trunk/include/llvm/LinkAllPasses.h Tue Mar 20 10:09:21 2018<br>
@@ -207,6 +207,7 @@ namespace {<br>
(void) llvm::createRewriteSymbolsPass();<br>
(void) llvm::createStraightLineStrengthReducePass();<br>
(void) llvm::createMemDerefPrinter();<br>
+ (void) llvm::createMustExecutePrinter();<br>
(void) llvm::createFloat2IntPass();<br>
(void) llvm::createEliminateAvailableExternallyPass();<br>
(void) llvm::createScalarizeMaskedMemIntrinPass();<br>
<br>
Modified: llvm/trunk/lib/Analysis/Analysis.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/Analysis.cpp?rev=328004&r1=328003&r2=328004&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/Analysis.cpp?rev=328004&r1=328003&r2=328004&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/Analysis/Analysis.cpp (original)<br>
+++ llvm/trunk/lib/Analysis/Analysis.cpp Tue Mar 20 10:09:21 2018<br>
@@ -65,6 +65,7 @@ void llvm::initializeAnalysis(PassRegist<br>
initializeMemoryDependenceWrapperPassPass(Registry);<br>
initializeModuleDebugInfoPrinterPass(Registry);<br>
initializeModuleSummaryIndexWrapperPassPass(Registry);<br>
+ initializeMustExecutePrinterPass(Registry);<br>
initializeObjCARCAAWrapperPassPass(Registry);<br>
initializeOptimizationRemarkEmitterWrapperPassPass(Registry);<br>
initializePostDominatorTreeWrapperPassPass(Registry);<br>
<br>
Modified: llvm/trunk/lib/Analysis/CMakeLists.txt<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/CMakeLists.txt?rev=328004&r1=328003&r2=328004&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/CMakeLists.txt?rev=328004&r1=328003&r2=328004&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/Analysis/CMakeLists.txt (original)<br>
+++ llvm/trunk/lib/Analysis/CMakeLists.txt Tue Mar 20 10:09:21 2018<br>
@@ -58,6 +58,7 @@ add_llvm_library(LLVMAnalysis<br>
MemorySSAUpdater.cpp<br>
ModuleDebugInfoPrinter.cpp<br>
ModuleSummaryAnalysis.cpp<br>
+ MustExecute.cpp<br>
ObjCARCAliasAnalysis.cpp<br>
ObjCARCAnalysisUtils.cpp<br>
ObjCARCInstKind.cpp<br>
<br>
Added: llvm/trunk/lib/Analysis/MustExecute.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MustExecute.cpp?rev=328004&view=auto" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MustExecute.cpp?rev=328004&view=auto</a><br>
==============================================================================<br>
--- llvm/trunk/lib/Analysis/MustExecute.cpp (added)<br>
+++ llvm/trunk/lib/Analysis/MustExecute.cpp Tue Mar 20 10:09:21 2018<br>
@@ -0,0 +1,102 @@<br>
+//===- MustExecute.cpp - Printer for isGuaranteedToExecute ----------------===//<br>
+//<br>
+// The LLVM Compiler Infrastructure<br>
+//<br>
+// This file is distributed under the University of Illinois Open Source<br>
+// License. See LICENSE.TXT for details.<br>
+//<br>
+//===----------------------------------------------------------------------===//<br>
+<br>
+#include "llvm/Analysis/LoopInfo.h"<br>
+#include "llvm/Analysis/Passes.h"<br>
+#include "llvm/Analysis/ValueTracking.h"<br>
+#include "llvm/IR/DataLayout.h"<br>
+#include "llvm/IR/InstIterator.h"<br>
+#include "llvm/IR/LLVMContext.h"<br>
+#include "llvm/IR/Module.h"<br>
+#include "llvm/Support/ErrorHandling.h"<br>
+#include "llvm/Support/raw_ostream.h"<br>
+#include "llvm/Transforms/Utils/LoopUtils.h"<br></blockquote><div><br>This looks like a circular/invalid dependency? Transforms depend on Analysis, not the other way around?<br><br>Would be great to get this fixed - happy to help, if you've some ideas.<br><br>Moving the whole LoopUtils isn't immediately possible, its implementation depends on BasicBlockUtils. (& also many of these utilities seem more for mutation, which isn't relevant to Analysis - so maybe it needs to be split up?)<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
+using namespace llvm;<br>
+<br>
+namespace {<br>
+ struct MustExecutePrinter : public FunctionPass {<br>
+ DenseMap<Value*, SmallVector<Loop*, 4> > MustExec;<br>
+ SmallVector<Value *, 4> Ordering;<br>
+<br>
+ static char ID; // Pass identification, replacement for typeid<br>
+ MustExecutePrinter() : FunctionPass(ID) {<br>
+ initializeMustExecutePrinterPass(*PassRegistry::getPassRegistry());<br>
+ }<br>
+ void getAnalysisUsage(AnalysisUsage &AU) const override {<br>
+ AU.setPreservesAll();<br>
+ AU.addRequired<DominatorTreeWrapperPass>();<br>
+ AU.addRequired<LoopInfoWrapperPass>();<br>
+ }<br>
+ bool runOnFunction(Function &F) override;<br>
+ void print(raw_ostream &OS, const Module * = nullptr) const override;<br>
+ void releaseMemory() override {<br>
+ MustExec.clear();<br>
+ Ordering.clear();<br>
+ }<br>
+ };<br>
+}<br>
+<br>
+char MustExecutePrinter::ID = 0;<br>
+INITIALIZE_PASS_BEGIN(MustExecutePrinter, "print-mustexecute",<br>
+ "Instructions which execute on loop entry", false, true)<br>
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)<br>
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)<br>
+INITIALIZE_PASS_END(MustExecutePrinter, "print-mustexecute",<br>
+ "Instructions which execute on loop entry", false, true)<br>
+<br>
+FunctionPass *llvm::createMustExecutePrinter() {<br>
+ return new MustExecutePrinter();<br>
+}<br>
+<br>
+bool isMustExecuteIn(Instruction &I, Loop *L, DominatorTree *DT) {<br>
+ // TODO: move loop specific code to analysis<br>
+ //LoopSafetyInfo LSI;<br>
+ //computeLoopSafetyInfo(&LSI, L);<br>
+ //return isGuaranteedToExecute(I, DT, L, &LSI);<br>
+ return isGuaranteedToExecuteForEveryIteration(&I, L);<br>
+}<br>
+<br>
+bool MustExecutePrinter::runOnFunction(Function &F) {<br>
+ auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();<br>
+ auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();<br>
+ for (auto &I: instructions(F)) {<br>
+ Loop *L = LI.getLoopFor(I.getParent());<br>
+ while (L) {<br>
+ if (isMustExecuteIn(I, L, &DT)) {<br>
+ if (!MustExec.count(&I))<br>
+ Ordering.push_back(&I);<br>
+ MustExec[&I].push_back(L);<br>
+ }<br>
+ L = L->getParentLoop();<br>
+ };<br>
+ }<br>
+ return false;<br>
+}<br>
+<br>
+void MustExecutePrinter::print(raw_ostream &OS, const Module *M) const {<br>
+ OS << "The following are guaranteed to execute (for the respective loops):\n";<br>
+ for (Value *V: Ordering) {<br>
+ V->printAsOperand(OS);<br>
+ auto NumLoops = MustExec.lookup(V).size();<br>
+ if (NumLoops > 1)<br>
+ OS << "\t(mustexec in " << NumLoops << " loops: ";<br>
+ else<br>
+ OS << "\t(mustexec in: ";<br>
+<br>
+ bool first = true;<br>
+ for (const Loop *L : MustExec.lookup(V)) {<br>
+ if (!first)<br>
+ OS << ", ";<br>
+ first = false;<br>
+ OS << L->getHeader()->getName();<br>
+ }<br>
+ OS << ")\n";<br>
+ }<br>
+ OS << "\n";<br>
+}<br>
<br>
Added: llvm/trunk/test/Analysis/MustExecute/loop-header.ll<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/MustExecute/loop-header.ll?rev=328004&view=auto" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/MustExecute/loop-header.ll?rev=328004&view=auto</a><br>
==============================================================================<br>
--- llvm/trunk/test/Analysis/MustExecute/loop-header.ll (added)<br>
+++ llvm/trunk/test/Analysis/MustExecute/loop-header.ll Tue Mar 20 10:09:21 2018<br>
@@ -0,0 +1,80 @@<br>
+; RUN: opt -analyze -print-mustexecute %s<br>
+<br>
+; CHECK: Printing analysis 'Instructions which execute on loop entry' for function 'header_with_icf':<br>
+; CHECK: The following are guaranteed to execute (for the respective loops):<br>
+; CHECK: %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ] (mustexec in: loop)<br>
+; CHECK: %v = load i32, i32* %p (mustexec in: loop)<br>
+; CHECK: call void @maythrow_and_use(i32 %v) (mustexec in: loop)<br>
+; CHECK-NOT: add<br>
+define i1 @header_with_icf(i32* noalias %p, i32 %high) {<br>
+entry:<br>
+ br label %loop<br>
+<br>
+loop:<br>
+ %iv = phi i32 [0, %entry], [%iv.next, %loop]<br>
+ %v = load i32, i32* %p<br>
+ call void @maythrow_and_use(i32 %v)<br>
+ %iv.next = add nsw nuw i32 %iv, 1<br>
+ %exit.test = icmp slt i32 %iv, %high<br>
+ br i1 %exit.test, label %exit, label %loop<br>
+<br>
+exit:<br>
+ ret i1 false<br>
+}<br>
+<br>
+; CHECK: Printing analysis 'Instructions which execute on loop entry' for function 'test':<br>
+; CHECK: The following are guaranteed to execute (for the respective loops):<br>
+; CHECK: %iv = phi i32 [ 0, %entry ], [ %iv.next, %next ] (mustexec in: loop)<br>
+; CHECK: %v = load i32, i32* %p (mustexec in: loop)<br>
+; CHECK: br label %next (mustexec in: loop)<br>
+define i1 @test(i32* noalias %p, i32 %high) {<br>
+entry:<br>
+ br label %loop<br>
+<br>
+loop:<br>
+ %iv = phi i32 [0, %entry], [%iv.next, %next]<br>
+ %v = load i32, i32* %p<br>
+ br label %next<br>
+next:<br>
+ call void @maythrow_and_use(i32 %v)<br>
+ %iv.next = add nsw nuw i32 %iv, 1<br>
+ %exit.test = icmp slt i32 %iv, %high<br>
+ br i1 %exit.test, label %exit, label %loop<br>
+<br>
+exit:<br>
+ ret i1 false<br>
+}<br>
+<br>
+; CHECK: Printing analysis 'Instructions which execute on loop entry' for function 'nested':<br>
+; CHECK: The following are guaranteed to execute (for the respective loops):<br>
+; CHECK: %iv = phi i32 [ 0, %entry ], [ %iv.next, %next ] (mustexec in: loop)<br>
+; CHECK: br label %inner_loop (mustexec in: loop)<br>
+; FIXME: These three are also must execute for the outer loop.<br>
+; CHECK: %v = load i32, i32* %p (mustexec in: inner_loop)<br>
+; CHECK: %inner.test = icmp eq i32 %v, 0 (mustexec in: inner_loop)<br>
+; CHECK: br i1 %inner.test, label %inner_loop, label %next (mustexec in: inner_loop)<br>
+define i1 @nested(i32* noalias %p, i32 %high) {<br>
+entry:<br>
+ br label %loop<br>
+<br>
+loop:<br>
+ %iv = phi i32 [0, %entry], [%iv.next, %next]<br>
+ br label %inner_loop<br>
+<br>
+inner_loop:<br>
+ %v = load i32, i32* %p<br>
+ %inner.test = icmp eq i32 %v, 0<br>
+ br i1 %inner.test, label %inner_loop, label %next<br>
+<br>
+next:<br>
+ call void @maythrow_and_use(i32 %v)<br>
+ %iv.next = add nsw nuw i32 %iv, 1<br>
+ %exit.test = icmp slt i32 %iv, %high<br>
+ br i1 %exit.test, label %exit, label %loop<br>
+<br>
+exit:<br>
+ ret i1 false<br>
+}<br>
+<br>
+<br>
+declare void @maythrow_and_use(i32)<br>
<br>
<br>
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</blockquote></div></div>