[HardwareLoops] Optimisation remarks
This adds the initial plumbing to support optimisation remarks in
the IR hardware-loop pass.
I have left a todo in a comment where we can improve the reporting,
and will iterate on that now that we have this initial support in.
Differential Revision: https://reviews.llvm.org/D68579
llvm-svn: 374980
diff --git a/llvm/lib/CodeGen/HardwareLoops.cpp b/llvm/lib/CodeGen/HardwareLoops.cpp
index 6a0f98d..968177c 100644
--- a/llvm/lib/CodeGen/HardwareLoops.cpp
+++ b/llvm/lib/CodeGen/HardwareLoops.cpp
@@ -21,6 +21,7 @@
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/TargetTransformInfo.h"
@@ -75,8 +76,44 @@
STATISTIC(NumHWLoops, "Number of loops converted to hardware loops");
+#ifndef NDEBUG
+static void debugHWLoopFailure(const StringRef DebugMsg,
+ Instruction *I) {
+ dbgs() << "HWLoops: " << DebugMsg;
+ if (I)
+ dbgs() << ' ' << *I;
+ else
+ dbgs() << '.';
+ dbgs() << '\n';
+}
+#endif
+
+static OptimizationRemarkAnalysis
+createHWLoopAnalysis(StringRef RemarkName, Loop *L, Instruction *I) {
+ Value *CodeRegion = L->getHeader();
+ DebugLoc DL = L->getStartLoc();
+
+ if (I) {
+ CodeRegion = I->getParent();
+ // If there is no debug location attached to the instruction, revert back to
+ // using the loop's.
+ if (I->getDebugLoc())
+ DL = I->getDebugLoc();
+ }
+
+ OptimizationRemarkAnalysis R(DEBUG_TYPE, RemarkName, DL, CodeRegion);
+ R << "hardware-loop not created: ";
+ return R;
+}
+
namespace {
+ void reportHWLoopFailure(const StringRef Msg, const StringRef ORETag,
+ OptimizationRemarkEmitter *ORE, Loop *TheLoop, Instruction *I = nullptr) {
+ LLVM_DEBUG(debugHWLoopFailure(Msg, I));
+ ORE->emit(createHWLoopAnalysis(ORETag, TheLoop, I) << Msg);
+ }
+
using TTI = TargetTransformInfo;
class HardwareLoops : public FunctionPass {
@@ -97,6 +134,7 @@
AU.addRequired<ScalarEvolutionWrapperPass>();
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetTransformInfoWrapperPass>();
+ AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
}
// Try to convert the given Loop into a hardware loop.
@@ -110,6 +148,7 @@
ScalarEvolution *SE = nullptr;
LoopInfo *LI = nullptr;
const DataLayout *DL = nullptr;
+ OptimizationRemarkEmitter *ORE = nullptr;
const TargetTransformInfo *TTI = nullptr;
DominatorTree *DT = nullptr;
bool PreserveLCSSA = false;
@@ -143,8 +182,9 @@
public:
HardwareLoop(HardwareLoopInfo &Info, ScalarEvolution &SE,
- const DataLayout &DL) :
- SE(SE), DL(DL), L(Info.L), M(L->getHeader()->getModule()),
+ const DataLayout &DL,
+ OptimizationRemarkEmitter *ORE) :
+ SE(SE), DL(DL), ORE(ORE), L(Info.L), M(L->getHeader()->getModule()),
ExitCount(Info.ExitCount),
CountType(Info.CountType),
ExitBranch(Info.ExitBranch),
@@ -157,6 +197,7 @@
private:
ScalarEvolution &SE;
const DataLayout &DL;
+ OptimizationRemarkEmitter *ORE = nullptr;
Loop *L = nullptr;
Module *M = nullptr;
const SCEV *ExitCount = nullptr;
@@ -182,6 +223,7 @@
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
DL = &F.getParent()->getDataLayout();
+ ORE = &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
LibInfo = TLIP ? &TLIP->getTLI(F) : nullptr;
PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
@@ -201,31 +243,39 @@
// converted and the parent loop doesn't support containing a hardware loop.
bool HardwareLoops::TryConvertLoop(Loop *L) {
// Process nested loops first.
- for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
- if (TryConvertLoop(*I))
+ for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) {
+ if (TryConvertLoop(*I)) {
+ reportHWLoopFailure("nested hardware-loops not supported", "HWLoopNested",
+ ORE, L);
return true; // Stop search.
-
- HardwareLoopInfo HWLoopInfo(L);
- if (!HWLoopInfo.canAnalyze(*LI))
- return false;
-
- if (TTI->isHardwareLoopProfitable(L, *SE, *AC, LibInfo, HWLoopInfo) ||
- ForceHardwareLoops) {
-
- // Allow overriding of the counter width and loop decrement value.
- if (CounterBitWidth.getNumOccurrences())
- HWLoopInfo.CountType =
- IntegerType::get(M->getContext(), CounterBitWidth);
-
- if (LoopDecrement.getNumOccurrences())
- HWLoopInfo.LoopDecrement =
- ConstantInt::get(HWLoopInfo.CountType, LoopDecrement);
-
- MadeChange |= TryConvertLoop(HWLoopInfo);
- return MadeChange && (!HWLoopInfo.IsNestingLegal && !ForceNestedLoop);
+ }
}
- return false;
+ HardwareLoopInfo HWLoopInfo(L);
+ if (!HWLoopInfo.canAnalyze(*LI)) {
+ reportHWLoopFailure("cannot analyze loop, irreducible control flow",
+ "HWLoopCannotAnalyze", ORE, L);
+ return false;
+ }
+
+ if (!ForceHardwareLoops &&
+ !TTI->isHardwareLoopProfitable(L, *SE, *AC, LibInfo, HWLoopInfo)) {
+ reportHWLoopFailure("it's not profitable to create a hardware-loop",
+ "HWLoopNotProfitable", ORE, L);
+ return false;
+ }
+
+ // Allow overriding of the counter width and loop decrement value.
+ if (CounterBitWidth.getNumOccurrences())
+ HWLoopInfo.CountType =
+ IntegerType::get(M->getContext(), CounterBitWidth);
+
+ if (LoopDecrement.getNumOccurrences())
+ HWLoopInfo.LoopDecrement =
+ ConstantInt::get(HWLoopInfo.CountType, LoopDecrement);
+
+ MadeChange |= TryConvertLoop(HWLoopInfo);
+ return MadeChange && (!HWLoopInfo.IsNestingLegal && !ForceNestedLoop);
}
bool HardwareLoops::TryConvertLoop(HardwareLoopInfo &HWLoopInfo) {
@@ -234,8 +284,13 @@
LLVM_DEBUG(dbgs() << "HWLoops: Try to convert profitable loop: " << *L);
if (!HWLoopInfo.isHardwareLoopCandidate(*SE, *LI, *DT, ForceNestedLoop,
- ForceHardwareLoopPHI))
+ ForceHardwareLoopPHI)) {
+ // TODO: there can be many reasons a loop is not considered a
+ // candidate, so we should let isHardwareLoopCandidate fill in the
+ // reason and then report a better message here.
+ reportHWLoopFailure("loop is not a candidate", "HWLoopNoCandidate", ORE, L);
return false;
+ }
assert(
(HWLoopInfo.ExitBlock && HWLoopInfo.ExitBranch && HWLoopInfo.ExitCount) &&
@@ -249,7 +304,7 @@
if (!Preheader)
return false;
- HardwareLoop HWLoop(HWLoopInfo, *SE, *DL);
+ HardwareLoop HWLoop(HWLoopInfo, *SE, *DL, ORE);
HWLoop.Create();
++NumHWLoops;
return true;
@@ -257,10 +312,13 @@
void HardwareLoop::Create() {
LLVM_DEBUG(dbgs() << "HWLoops: Converting loop..\n");
-
+
Value *LoopCountInit = InitLoopCount();
- if (!LoopCountInit)
+ if (!LoopCountInit) {
+ reportHWLoopFailure("could not safely create a loop count expression",
+ "HWLoopNotSafe", ORE, L);
return;
+ }
InsertIterationSetup(LoopCountInit);