From d63a2bb35fb25ca17b3cb6e82bcb2050179381b0 Mon Sep 17 00:00:00 2001 From: Bjorn Pettersson Date: Fri, 24 May 2019 08:32:02 +0000 Subject: [PATCH] [DSE] Bugfix to avoid PartialStoreMerging involving non byte-sized stores Summary: The DeadStoreElimination pass now skips doing PartialStoreMerging when stores overlap according to OW_PartialEarlierWithFullLater and at least one of the stores is having a store size that is different from the size of the type being stored. This solves problems seen in https://bugs.llvm.org/show_bug.cgi?id=41949 for which we in the past could end up with mis-compiles or assertions. The content and location of the padding bits is not formally described (or undefined) in the LangRef at the moment. So the solution is chosen based on that we cannot assume anything about the padding bits when having a store that clobbers more memory than indicated by the type of the value that is stored (such as storing an i6 using an 8-bit store instruction). Fixes: https://bugs.llvm.org/show_bug.cgi?id=41949 Reviewers: spatel, efriedma, fhahn Reviewed By: efriedma Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D62250 llvm-svn: 361605 --- llvm/include/llvm/IR/DataLayout.h | 8 ++++ .../lib/Transforms/Scalar/DeadStoreElimination.cpp | 5 ++ .../DeadStoreElimination/PartialStore2.ll | 55 ++++++++++++++++++++++ 3 files changed, 68 insertions(+) create mode 100644 llvm/test/Transforms/DeadStoreElimination/PartialStore2.ll diff --git a/llvm/include/llvm/IR/DataLayout.h b/llvm/include/llvm/IR/DataLayout.h index 05c72f1..ac9770a 100644 --- a/llvm/include/llvm/IR/DataLayout.h +++ b/llvm/include/llvm/IR/DataLayout.h @@ -453,6 +453,14 @@ public: return 8 * getTypeStoreSize(Ty); } + /// Returns true if no extra padding bits are needed when storing the + /// specified type. + /// + /// For example, returns false for i19 that has a 24-bit store size. + bool typeSizeEqualsStoreSize(Type *Ty) const { + return getTypeSizeInBits(Ty) == getTypeStoreSizeInBits(Ty); + } + /// Returns the offset in bytes between successive objects of the /// specified type, including alignment padding. /// diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp index 75206c2..a816457 100644 --- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp +++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp @@ -1211,12 +1211,17 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA, auto *Earlier = dyn_cast(DepWrite); auto *Later = dyn_cast(Inst); if (Earlier && isa(Earlier->getValueOperand()) && + DL.typeSizeEqualsStoreSize( + Earlier->getValueOperand()->getType()) && Later && isa(Later->getValueOperand()) && + DL.typeSizeEqualsStoreSize( + Later->getValueOperand()->getType()) && memoryIsNotModifiedBetween(Earlier, Later, AA)) { // If the store we find is: // a) partially overwritten by the store to 'Loc' // b) the later store is fully contained in the earlier one and // c) they both have a constant value + // d) none of the two stores need padding // Merge the two stores, replacing the earlier store's value with a // merge of both values. // TODO: Deal with other constant types (vectors, etc), and probably diff --git a/llvm/test/Transforms/DeadStoreElimination/PartialStore2.ll b/llvm/test/Transforms/DeadStoreElimination/PartialStore2.ll new file mode 100644 index 0000000..ebcb0c3 --- /dev/null +++ b/llvm/test/Transforms/DeadStoreElimination/PartialStore2.ll @@ -0,0 +1,55 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py +; RUN: opt < %s --data-layout "e" -dse -enable-dse-partial-store-merging=true -S | FileCheck --check-prefix CHECK --check-prefix CHECK-LE %s +; RUN: opt < %s --data-layout "E" -dse -enable-dse-partial-store-merging=true -S | FileCheck --check-prefix CHECK --check-prefix CHECK-BE %s + +; This test used to hit an assertion (see PR41949). +; +; Better safe than sorry, do not assume anything about the padding for the +; i28 store that has 32 bits as store size. +define void @test1(i32* %p) { +; CHECK-LABEL: @test1( +; CHECK-NEXT: [[A:%.*]] = alloca i32 +; CHECK-NEXT: [[B:%.*]] = bitcast i32* [[A]] to i28* +; CHECK-NEXT: [[C:%.*]] = bitcast i32* [[A]] to { i16, i16 }* +; CHECK-NEXT: [[C1:%.*]] = getelementptr inbounds { i16, i16 }, { i16, i16 }* [[C]], i32 0, i32 1 +; CHECK-NEXT: store i28 10, i28* [[B]] +; CHECK-NEXT: store i16 20, i16* [[C1]] +; CHECK-NEXT: call void @test1(i32* [[A]]) +; CHECK-NEXT: ret void +; + %a = alloca i32 + %b = bitcast i32* %a to i28* + %c = bitcast i32* %a to { i16, i16 }* + %c1 = getelementptr inbounds { i16, i16 }, { i16, i16 }* %c, i32 0, i32 1 + store i28 10, i28* %b + store i16 20, i16* %c1 + + call void @test1(i32* %a) + ret void +} + + +; This test used to mis-compile (see PR41949). +; +; Better safe than sorry, do not assume anything about the padding for the +; i12 store that has 16 bits as store size. +define void @test2(i32* %p) { +; CHECK-LABEL: @test2( +; CHECK-NEXT: [[U:%.*]] = alloca i32 +; CHECK-NEXT: [[A:%.*]] = bitcast i32* [[U]] to i32* +; CHECK-NEXT: [[B:%.*]] = bitcast i32* [[U]] to i12* +; CHECK-NEXT: store i32 -1, i32* [[A]] +; CHECK-NEXT: store i12 20, i12* [[B]] +; CHECK-NEXT: call void @test2(i32* [[U]]) +; CHECK-NEXT: ret void +; + %u = alloca i32 + %a = bitcast i32* %u to i32* + %b = bitcast i32* %u to i12* + store i32 -1, i32* %a + store i12 20, i12* %b + + call void @test2(i32* %u) + ret void +} + -- 2.7.4