[llvm] [ObjectSizeOffsetVisitor] Add a max recursion depth (PR #67479)
Arthur Eubanks via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 26 12:53:39 PDT 2023
https://github.com/aeubanks created https://github.com/llvm/llvm-project/pull/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.
>From 6e42937cc41cf1d2d5ff3d215253dbf4f6b08fc2 Mon Sep 17 00:00:00 2001
From: Arthur Eubanks <aeubanks at google.com>
Date: Tue, 26 Sep 2023 12:50:08 -0700
Subject: [PATCH] [ObjectSizeOffsetVisitor] Add a max recursion depth
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.
---
llvm/include/llvm/Analysis/MemoryBuiltins.h | 1 +
llvm/lib/Analysis/MemoryBuiltins.cpp | 25 ++++++--
...bject-size-offset-visitor-max-recursion.ll | 63 +++++++++++++++++++
3 files changed, 83 insertions(+), 6 deletions(-)
create mode 100644 llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-recursion.ll
diff --git a/llvm/include/llvm/Analysis/MemoryBuiltins.h b/llvm/include/llvm/Analysis/MemoryBuiltins.h
index 1d9831889f573ab..49e5b69898427d1 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 RecurseDepth = 0;
APInt align(APInt Size, MaybeAlign Align);
diff --git a/llvm/lib/Analysis/MemoryBuiltins.cpp b/llvm/lib/Analysis/MemoryBuiltins.cpp
index 9eab801c3ccbb97..d727e8214dc7938 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> ObjectSizeOffsetVisitorMaxRecurseDepth(
+ "object-size-offset-visitor-max-recurse-depth",
+ cl::desc(
+ "Maximum number of PHIs for ObjectSizeOffsetVisitor to look through"),
+ cl::init(100));
+
enum AllocType : uint8_t {
OpNewLike = 1<<0, // allocates; never returns null
MallocLike = 1<<1, // allocates; may return null
@@ -994,14 +1001,20 @@ SizeOffsetType ObjectSizeOffsetVisitor::combineSizeOffset(SizeOffsetType LHS,
}
SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode &PN) {
- if (PN.getNumIncomingValues() == 0)
+ if (PN.getNumIncomingValues() == 0 ||
+ RecurseDepth >= ObjectSizeOffsetVisitorMaxRecurseDepth)
return unknown();
+
+ ++RecurseDepth;
auto IncomingValues = PN.incoming_values();
- return std::accumulate(IncomingValues.begin() + 1, IncomingValues.end(),
- compute(*IncomingValues.begin()),
- [this](SizeOffsetType LHS, Value *VRHS) {
- return combineSizeOffset(LHS, compute(VRHS));
- });
+ SizeOffsetType Ret =
+ std::accumulate(IncomingValues.begin() + 1, IncomingValues.end(),
+ compute(*IncomingValues.begin()),
+ [this](SizeOffsetType LHS, Value *VRHS) {
+ return combineSizeOffset(LHS, compute(VRHS));
+ });
+ --RecurseDepth;
+ return Ret;
}
SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
diff --git a/llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-recursion.ll b/llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-recursion.ll
new file mode 100644
index 000000000000000..ee6db23f13581d4
--- /dev/null
+++ b/llvm/test/Transforms/DeadStoreElimination/object-size-offset-visitor-max-recursion.ll
@@ -0,0 +1,63 @@
+; 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-recurse-depth=1 < %s | FileCheck %s --check-prefix=NO
+; RUN: opt -passes=dse -S -object-size-offset-visitor-max-recurse-depth=2 < %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: [[A3:%.*]] = phi ptr [ [[A1]], [[B0:%.*]] ]
+; NO-NEXT: br label [[B3:%.*]]
+; NO: b2:
+; NO-NEXT: [[A4:%.*]] = phi ptr [ [[A2]], [[B0]] ]
+; NO-NEXT: br label [[B3]]
+; NO: b3:
+; NO-NEXT: [[A5:%.*]] = phi ptr [ [[A3]], [[B1]] ], [ [[A4]], [[B2]] ]
+; 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: [[A3:%.*]] = phi ptr [ [[A1]], [[B0:%.*]] ]
+; YES-NEXT: br label [[B3:%.*]]
+; YES: b2:
+; YES-NEXT: [[A4:%.*]] = phi ptr [ [[A2]], [[B0]] ]
+; YES-NEXT: br label [[B3]]
+; YES: b3:
+; YES-NEXT: [[A5:%.*]] = phi ptr [ [[A3]], [[B1]] ], [ [[A4]], [[B2]] ]
+; 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:
+ %a3 = phi ptr [ %a1, %b0 ]
+ br label %b3
+b2:
+ %a4 = phi ptr [ %a2, %b0 ]
+ br label %b3
+b3:
+ %a5 = phi ptr [ %a3, %b1 ], [ %a4, %b2 ]
+ %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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