From 4e89d1199c180fd384486ba2796368ec800180ee Mon Sep 17 00:00:00 2001 From: Yingwei Zheng Date: Thu, 1 Aug 2024 22:46:07 +0800 Subject: [PATCH] [InstCombine] Convert mem intrinsic with null into a noop (#100388) When src/dest passed into memset/memcpy is null: ``` len == 0: this call is a noop. len != 0: the behavior is undefined. ``` See also https://llvm.org/docs/LangRef.html#llvm-memset-intrinsics Alive2: https://alive2.llvm.org/ce/z/tJeRNL This patch converts these mem intrinsic calls into an assumption `len == 0` to mitigate code-size bloat caused by JumpThreading. --- .../InstCombine/InstCombineCalls.cpp | 14 ++++ .../Transforms/InstCombine/mem-intrinsics.ll | 77 +++++++++++++++++++ llvm/test/Transforms/InstCombine/mempcpy.ll | 2 +- 3 files changed, 92 insertions(+), 1 deletion(-) create mode 100644 llvm/test/Transforms/InstCombine/mem-intrinsics.ll diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp index deb8e3cb6fabc9..cc68fd4cf1c1b6 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp @@ -1584,16 +1584,30 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) { return eraseInstFromFunction(CI); } + auto IsPointerUndefined = [MI](Value *Ptr) { + return isa(Ptr) && + !NullPointerIsDefined( + MI->getFunction(), + cast(Ptr->getType())->getAddressSpace()); + }; + bool SrcIsUndefined = false; // If we can determine a pointer alignment that is bigger than currently // set, update the alignment. if (auto *MTI = dyn_cast(MI)) { if (Instruction *I = SimplifyAnyMemTransfer(MTI)) return I; + SrcIsUndefined = IsPointerUndefined(MTI->getRawSource()); } else if (auto *MSI = dyn_cast(MI)) { if (Instruction *I = SimplifyAnyMemSet(MSI)) return I; } + // If src/dest is null, this memory intrinsic must be a noop. + if (SrcIsUndefined || IsPointerUndefined(MI->getRawDest())) { + Builder.CreateAssumption(Builder.CreateIsNull(MI->getLength())); + return eraseInstFromFunction(CI); + } + if (Changed) return II; } diff --git a/llvm/test/Transforms/InstCombine/mem-intrinsics.ll b/llvm/test/Transforms/InstCombine/mem-intrinsics.ll new file mode 100644 index 00000000000000..5448d3c20fb126 --- /dev/null +++ b/llvm/test/Transforms/InstCombine/mem-intrinsics.ll @@ -0,0 +1,77 @@ +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 +; RUN: opt -S -passes=instcombine < %s | FileCheck %s + +define void @memset_null(i64 %len) { +; CHECK-LABEL: define void @memset_null( +; CHECK-SAME: i64 [[LEN:%.*]]) { +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0 +; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]]) +; CHECK-NEXT: ret void +; + call void @llvm.memset.p0.i64(ptr null, i8 0, i64 %len, i1 false) + ret void +} + +define void @memset_null_ub() { +; CHECK-LABEL: define void @memset_null_ub() { +; CHECK-NEXT: store i64 poison, ptr null, align 4294967296 +; CHECK-NEXT: ret void +; + call void @llvm.memset.p0.i64(ptr null, i8 0, i64 8, i1 false) + ret void +} + +define void @memcpy_null_src(ptr %dst, i64 %len) { +; CHECK-LABEL: define void @memcpy_null_src( +; CHECK-SAME: ptr [[DST:%.*]], i64 [[LEN:%.*]]) { +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0 +; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]]) +; CHECK-NEXT: ret void +; + call void @llvm.memcpy.p0.i64(ptr %dst, ptr null, i64 %len, i1 false) + ret void +} + +define void @memmove_null_src(ptr %dst, i64 %len) { +; CHECK-LABEL: define void @memmove_null_src( +; CHECK-SAME: ptr [[DST:%.*]], i64 [[LEN:%.*]]) { +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0 +; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]]) +; CHECK-NEXT: ret void +; + call void @llvm.memmove.p0.i64(ptr %dst, ptr null, i64 %len, i1 false) + ret void +} + +define void @memset_element_atomic(i64 %len) { +; CHECK-LABEL: define void @memset_element_atomic( +; CHECK-SAME: i64 [[LEN:%.*]]) { +; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0 +; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]]) +; CHECK-NEXT: ret void +; + call void @llvm.memset.element.unordered.atomic.p0.i64(ptr align 1 null, i8 0, i64 %len, i32 1) + ret void +} + +; negative tests + +define void @memset_null_volatile(i64 %len) { +; CHECK-LABEL: define void @memset_null_volatile( +; CHECK-SAME: i64 [[LEN:%.*]]) { +; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr null, i8 0, i64 [[LEN]], i1 true) +; CHECK-NEXT: ret void +; + call void @llvm.memset.p0.i64(ptr null, i8 0, i64 %len, i1 true) + ret void +} + +define void @memset_null_is_defined(i64 %len) null_pointer_is_valid { +; CHECK-LABEL: define void @memset_null_is_defined( +; CHECK-SAME: i64 [[LEN:%.*]]) #[[ATTR0:[0-9]+]] { +; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 4294967296 null, i8 0, i64 [[LEN]], i1 false) +; CHECK-NEXT: ret void +; + call void @llvm.memset.p0.i64(ptr null, i8 0, i64 %len, i1 false) + ret void +} diff --git a/llvm/test/Transforms/InstCombine/mempcpy.ll b/llvm/test/Transforms/InstCombine/mempcpy.ll index c996758a919d9a..82c34f8a864ce7 100644 --- a/llvm/test/Transforms/InstCombine/mempcpy.ll +++ b/llvm/test/Transforms/InstCombine/mempcpy.ll @@ -55,7 +55,7 @@ define ptr @memcpy_big_const_n(ptr %d, ptr nocapture readonly %s) { define i32 @PR48810() { ; CHECK-LABEL: @PR48810( -; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 1 undef, ptr align 4294967296 null, i64 undef, i1 false) +; CHECK-NEXT: store i1 true, ptr poison, align 1 ; CHECK-NEXT: ret i32 undef ; %r = call dereferenceable(1) ptr @mempcpy(ptr undef, ptr null, i64 undef)