[llvm] cf7eac9 - [ObjectSizeOffsetVisitor] Bail after visiting 100 instructions (#67479)
via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 27 05:54:45 PDT 2023
Author: Arthur Eubanks
Date: 2023-09-27T14:54:41+02:00
New Revision: cf7eac9650f3ce40154e5e35734a147599495af4
URL: https://github.com/llvm/llvm-project/commit/cf7eac9650f3ce40154e5e35734a147599495af4
DIFF: https://github.com/llvm/llvm-project/commit/cf7eac9650f3ce40154e5e35734a147599495af4.diff
LOG: [ObjectSizeOffsetVisitor] Bail after visiting 100 instructions (#67479)
We're running into stack overflows for huge functions with lots of phis.
Even without the stack overflows, this is recursing >7000 in some
auto-generated code.
This fixes the stack overflow and brings down the compile time to
something reasonable.
Added:
llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-visit-instructions.ll
Modified:
llvm/include/llvm/Analysis/MemoryBuiltins.h
llvm/lib/Analysis/MemoryBuiltins.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/MemoryBuiltins.h b/llvm/include/llvm/Analysis/MemoryBuiltins.h
index 1d9831889f573ab..827b5081b2ce755 100644
--- a/llvm/include/llvm/Analysis/MemoryBuiltins.h
+++ b/llvm/include/llvm/Analysis/MemoryBuiltins.h
@@ -199,6 +199,7 @@ class ObjectSizeOffsetVisitor
unsigned IntTyBits;
APInt Zero;
SmallDenseMap<Instruction *, SizeOffsetType, 8> SeenInsts;
+ unsigned InstructionsVisited;
APInt align(APInt Size, MaybeAlign Align);
@@ -248,6 +249,7 @@ class ObjectSizeOffsetVisitor
unsigned &ScannedInstCount);
SizeOffsetType combineSizeOffset(SizeOffsetType LHS, SizeOffsetType RHS);
SizeOffsetType computeImpl(Value *V);
+ SizeOffsetType computeValue(Value *V);
bool CheckedZextOrTrunc(APInt &I);
};
diff --git a/llvm/lib/Analysis/MemoryBuiltins.cpp b/llvm/lib/Analysis/MemoryBuiltins.cpp
index 9eab801c3ccbb97..6ee1984f908b8a1 100644
--- a/llvm/lib/Analysis/MemoryBuiltins.cpp
+++ b/llvm/lib/Analysis/MemoryBuiltins.cpp
@@ -35,6 +35,7 @@
#include "llvm/IR/Type.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
@@ -50,6 +51,12 @@ using namespace llvm;
#define DEBUG_TYPE "memory-builtins"
+static cl::opt<unsigned> ObjectSizeOffsetVisitorMaxVisitInstructions(
+ "object-size-offset-visitor-max-visit-instructions",
+ cl::desc("Maximum number of instructions for ObjectSizeOffsetVisitor to "
+ "look at"),
+ cl::init(100));
+
enum AllocType : uint8_t {
OpNewLike = 1<<0, // allocates; never returns null
MallocLike = 1<<1, // allocates; may return null
@@ -694,6 +701,11 @@ ObjectSizeOffsetVisitor::ObjectSizeOffsetVisitor(const DataLayout &DL,
}
SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
+ InstructionsVisited = 0;
+ return computeImpl(V);
+}
+
+SizeOffsetType ObjectSizeOffsetVisitor::computeImpl(Value *V) {
unsigned InitialIntTyBits = DL.getIndexTypeSizeInBits(V->getType());
// Stripping pointer casts can strip address space casts which can change the
@@ -710,14 +722,15 @@ SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
IntTyBits = DL.getIndexTypeSizeInBits(V->getType());
Zero = APInt::getZero(IntTyBits);
+ SizeOffsetType SOT = computeValue(V);
+
bool IndexTypeSizeChanged = InitialIntTyBits != IntTyBits;
if (!IndexTypeSizeChanged && Offset.isZero())
- return computeImpl(V);
+ return SOT;
// We stripped an address space cast that changed the index type size or we
// accumulated some constant offset (or both). Readjust the bit width to match
// the argument index type size and apply the offset, as required.
- SizeOffsetType SOT = computeImpl(V);
if (IndexTypeSizeChanged) {
if (knownSize(SOT) && !::CheckedZextOrTrunc(SOT.first, InitialIntTyBits))
SOT.first = APInt();
@@ -729,13 +742,16 @@ SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
SOT.second.getBitWidth() > 1 ? SOT.second + Offset : SOT.second};
}
-SizeOffsetType ObjectSizeOffsetVisitor::computeImpl(Value *V) {
+SizeOffsetType ObjectSizeOffsetVisitor::computeValue(Value *V) {
if (Instruction *I = dyn_cast<Instruction>(V)) {
// If we have already seen this instruction, bail out. Cycles can happen in
// unreachable code after constant propagation.
auto P = SeenInsts.try_emplace(I, unknown());
if (!P.second)
return P.first->second;
+ ++InstructionsVisited;
+ if (InstructionsVisited > ObjectSizeOffsetVisitorMaxVisitInstructions)
+ return unknown();
SizeOffsetType Res = visit(*I);
// Cache the result for later visits. If we happened to visit this during
// the above recursion, we would consider it unknown until now.
@@ -830,7 +846,7 @@ ObjectSizeOffsetVisitor::visitExtractValueInst(ExtractValueInst&) {
SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalAlias(GlobalAlias &GA) {
if (GA.isInterposable())
return unknown();
- return compute(GA.getAliasee());
+ return computeImpl(GA.getAliasee());
}
SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalVariable(GlobalVariable &GV){
@@ -885,7 +901,7 @@ SizeOffsetType ObjectSizeOffsetVisitor::findLoadSizeOffset(
continue;
case AliasResult::MustAlias:
if (SI->getValueOperand()->getType()->isPointerTy())
- return Known(compute(SI->getValueOperand()));
+ return Known(computeImpl(SI->getValueOperand()));
else
return Unknown(); // No handling of non-pointer values by `compute`.
default:
@@ -998,15 +1014,15 @@ SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode &PN) {
return unknown();
auto IncomingValues = PN.incoming_values();
return std::accumulate(IncomingValues.begin() + 1, IncomingValues.end(),
- compute(*IncomingValues.begin()),
+ computeImpl(*IncomingValues.begin()),
[this](SizeOffsetType LHS, Value *VRHS) {
- return combineSizeOffset(LHS, compute(VRHS));
+ return combineSizeOffset(LHS, computeImpl(VRHS));
});
}
SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
- return combineSizeOffset(compute(I.getTrueValue()),
- compute(I.getFalseValue()));
+ return combineSizeOffset(computeImpl(I.getTrueValue()),
+ computeImpl(I.getFalseValue()));
}
SizeOffsetType ObjectSizeOffsetVisitor::visitUndefValue(UndefValue&) {
diff --git a/llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-visit-instructions.ll b/llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-visit-instructions.ll
new file mode 100644
index 000000000000000..b94ff6289588284
--- /dev/null
+++ b/llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-visit-instructions.ll
@@ -0,0 +1,51 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -passes=dse -S -object-size-offset-visitor-max-visit-instructions=2 < %s | FileCheck %s --check-prefix=NO
+; RUN: opt -passes=dse -S -object-size-offset-visitor-max-visit-instructions=3 < %s | FileCheck %s --check-prefix=YES
+
+declare void @use(ptr)
+
+define void @f(i32 %i, i1 %c) {
+; NO-LABEL: define void @f(
+; NO-SAME: i32 [[I:%.*]], i1 [[C:%.*]]) {
+; NO-NEXT: b0:
+; NO-NEXT: [[A1:%.*]] = alloca i32, align 4
+; NO-NEXT: [[A2:%.*]] = alloca i32, align 4
+; NO-NEXT: br i1 [[C]], label [[B1:%.*]], label [[B2:%.*]]
+; NO: b1:
+; NO-NEXT: br label [[B2]]
+; NO: b2:
+; NO-NEXT: [[A5:%.*]] = phi ptr [ [[A1]], [[B0:%.*]] ], [ [[A2]], [[B1]] ]
+; NO-NEXT: [[G:%.*]] = getelementptr i8, ptr [[A5]], i32 [[I]]
+; NO-NEXT: store i8 1, ptr [[G]], align 1
+; NO-NEXT: store i32 0, ptr [[A5]], align 4
+; NO-NEXT: call void @use(ptr [[A5]])
+; NO-NEXT: ret void
+;
+; YES-LABEL: define void @f(
+; YES-SAME: i32 [[I:%.*]], i1 [[C:%.*]]) {
+; YES-NEXT: b0:
+; YES-NEXT: [[A1:%.*]] = alloca i32, align 4
+; YES-NEXT: [[A2:%.*]] = alloca i32, align 4
+; YES-NEXT: br i1 [[C]], label [[B1:%.*]], label [[B2:%.*]]
+; YES: b1:
+; YES-NEXT: br label [[B2]]
+; YES: b2:
+; YES-NEXT: [[A5:%.*]] = phi ptr [ [[A1]], [[B0:%.*]] ], [ [[A2]], [[B1]] ]
+; YES-NEXT: store i32 0, ptr [[A5]], align 4
+; YES-NEXT: call void @use(ptr [[A5]])
+; YES-NEXT: ret void
+;
+b0:
+ %a1 = alloca i32
+ %a2 = alloca i32
+ br i1 %c, label %b1, label %b2
+b1:
+ br label %b2
+b2:
+ %a5 = phi ptr [ %a1, %b0 ], [ %a2, %b1 ]
+ %g = getelementptr i8, ptr %a5, i32 %i
+ store i8 1, ptr %g
+ store i32 0, ptr %a5
+ call void @use(ptr %a5)
+ ret void
+}
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