[llvm] r288381 - [GVN, OptDiag] Print the interesting instructions involved in missed load-elimination
Adam Nemet via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 1 09:34:50 PST 2016
Author: anemet
Date: Thu Dec 1 11:34:50 2016
New Revision: 288381
URL: http://llvm.org/viewvc/llvm-project?rev=288381&view=rev
Log:
[GVN, OptDiag] Print the interesting instructions involved in missed load-elimination
[recommitting after the fix in r288307]
This includes the intervening store and the load/store that we're trying
to forward from in the optimization remark for the missed load
elimination.
This is hooked up under a new mode in ORE that allows for compile-time
budget for a bit more analysis to print more insightful messages. This
mode is currently enabled for -fsave-optimization-record (-Rpass is
trickier since it is controlled in the front-end).
With this we can now print the red remark in http://lab.llvm.org:8080/artifacts/opt-view_test-suite/build/SingleSource/Benchmarks/Dhrystone/CMakeFiles/dry.dir/html/_org_test-suite_SingleSource_Benchmarks_Dhrystone_dry.c.html#L446
Differential Revision: https://reviews.llvm.org/D26490
Modified:
llvm/trunk/include/llvm/Analysis/OptimizationDiagnosticInfo.h
llvm/trunk/lib/Transforms/Scalar/GVN.cpp
llvm/trunk/test/Transforms/GVN/opt-remarks.ll
Modified: llvm/trunk/include/llvm/Analysis/OptimizationDiagnosticInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/OptimizationDiagnosticInfo.h?rev=288381&r1=288380&r2=288381&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/OptimizationDiagnosticInfo.h (original)
+++ llvm/trunk/include/llvm/Analysis/OptimizationDiagnosticInfo.h Thu Dec 1 11:34:50 2016
@@ -18,12 +18,12 @@
#include "llvm/ADT/Optional.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Function.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
namespace llvm {
class DebugLoc;
-class Function;
class LLVMContext;
class Loop;
class Pass;
@@ -194,6 +194,19 @@ public:
void emitOptimizationRemarkAnalysisAliasing(const char *PassName, Loop *L,
const Twine &Msg);
+ /// \brief Whether we allow for extra compile-time budget to perform more
+ /// analysis to produce fewer false positives.
+ ///
+ /// This is useful when reporting missed optimizations. In this case we can
+ /// use the extra analysis (1) to filter trivial false positives or (2) to
+ /// provide more context so that non-trivial false positives can be quickly
+ /// detected by the user.
+ bool allowExtraAnalysis() const {
+ // For now, only allow this with -fsave-optimization-record since the -Rpass
+ // options are handled in the front-end.
+ return F->getContext().getDiagnosticsOutputFile();
+ }
+
private:
Function *F;
Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=288381&r1=288380&r2=288381&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Thu Dec 1 11:34:50 2016
@@ -1209,6 +1209,38 @@ static bool isLifetimeStart(const Instru
return false;
}
+/// \brief Try to locate the three instruction involved in a missed
+/// load-elimination case that is due to an intervening store.
+static void reportMayClobberedLoad(LoadInst *LI, MemDepResult DepInfo,
+ DominatorTree *DT,
+ OptimizationRemarkEmitter *ORE) {
+ using namespace ore;
+ User *OtherAccess = nullptr;
+
+ OptimizationRemarkMissed R(DEBUG_TYPE, "LoadClobbered", LI);
+ R << "load of type " << NV("Type", LI->getType()) << " not eliminated"
+ << setExtraArgs();
+
+ for (auto *U : LI->getPointerOperand()->users())
+ if (U != LI && (isa<LoadInst>(U) || isa<StoreInst>(U)) &&
+ DT->dominates(cast<Instruction>(U), LI)) {
+ // FIXME: for now give up if there are multiple memory accesses that
+ // dominate the load. We need further analysis to decide which one is
+ // that we're forwarding from.
+ if (OtherAccess)
+ OtherAccess = nullptr;
+ else
+ OtherAccess = U;
+ }
+
+ if (OtherAccess)
+ R << " in favor of " << NV("OtherAccess", OtherAccess);
+
+ R << " because it is clobbered by " << NV("ClobberedBy", DepInfo.getInst());
+
+ ORE->emit(R);
+}
+
bool GVN::AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
Value *Address, AvailableValue &Res) {
@@ -1273,6 +1305,10 @@ bool GVN::AnalyzeLoadAvailability(LoadIn
Instruction *I = DepInfo.getInst();
dbgs() << " is clobbered by " << *I << '\n';
);
+
+ if (ORE->allowExtraAnalysis())
+ reportMayClobberedLoad(LI, DepInfo, DT, ORE);
+
return false;
}
assert(DepInfo.isDef() && "follows from above");
Modified: llvm/trunk/test/Transforms/GVN/opt-remarks.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/opt-remarks.ll?rev=288381&r1=288380&r2=288381&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GVN/opt-remarks.ll (original)
+++ llvm/trunk/test/Transforms/GVN/opt-remarks.ll Thu Dec 1 11:34:50 2016
@@ -40,7 +40,22 @@
; YAML-NEXT: - String: ' in favor of '
; YAML-NEXT: - InfavorOfValue: load
; YAML-NEXT: ...
-
+; YAML-NEXT: --- !Missed
+; YAML-NEXT: Pass: gvn
+; YAML-NEXT: Name: LoadClobbered
+; YAML-NEXT: DebugLoc: { File: /tmp/s.c, Line: 3, Column: 3 }
+; YAML-NEXT: Function: may_alias
+; YAML-NEXT: Args:
+; YAML-NEXT: - String: 'load of type '
+; YAML-NEXT: - Type: i32
+; YAML-NEXT: - String: ' not eliminated'
+; YAML-NEXT: - String: ' in favor of '
+; YAML-NEXT: - OtherAccess: load
+; YAML-NEXT: DebugLoc: { File: /tmp/s.c, Line: 1, Column: 13 }
+; YAML-NEXT: - String: ' because it is clobbered by '
+; YAML-NEXT: - ClobberedBy: store
+; YAML-NEXT: DebugLoc: { File: /tmp/s.c, Line: 2, Column: 10 }
+; YAML-NEXT: ...
define i32 @arg(i32* %p, i32 %i) {
entry:
@@ -63,3 +78,31 @@ entry:
%add = add i32 %load1, %load
ret i32 %add
}
+
+define i32 @may_alias(i32* %p, i32* %r) !dbg !7 {
+entry:
+ %load1 = load i32, i32* %p, !tbaa !13, !dbg !9
+ store i32 4, i32* %r, !tbaa !13, !dbg !10
+ %load = load i32, i32* %p, !tbaa !13, !dbg !11
+ %add = add i32 %load1, %load
+ ret i32 %add
+}
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 4.0.0 (trunk 282540) (llvm/trunk 282542)", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "/tmp/s.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"PIC Level", i32 2}
+!6 = !{!"clang version 4.0.0 (trunk 282540) (llvm/trunk 282542)"}
+!7 = distinct !DISubprogram(name: "may_alias", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: true, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 1, column: 13, scope: !7)
+!10 = !DILocation(line: 2, column: 10, scope: !7)
+!11 = !DILocation(line: 3, column: 3, scope: !7)
+
+!12 = !{ !"tbaa root" }
+!13 = !{ !"int", !12 }
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