From 03bc2a070d14c4f99d12dc8de5b57f7067a7c6c6 Mon Sep 17 00:00:00 2001 From: zoecarver Date: Fri, 8 May 2020 12:22:39 -0700 Subject: [PATCH] Re-commit: Mark values as trivially dead when their only use is a start or end lifetime intrinsic. Summary: If the only use of a value is a start or end lifetime intrinsic then mark the intrinsic as trivially dead. This should allow for that value to then be removed as well. Currently, this only works for allocas, globals, and arguments. Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D79355 --- lib/Transforms/Utils/Local.cpp | 19 +++++- test/Analysis/BasicAA/modref.ll | 1 - .../Transforms/Attributor/memory_locations.ll | 6 +- test/Transforms/DCE/basic.ll | 58 +++++++++++++++++++ .../DeadStoreElimination/lifetime.ll | 4 +- test/Transforms/InstCombine/vararg.ll | 2 +- 6 files changed, 79 insertions(+), 11 deletions(-) diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp index 265d6d9337d..6d6e74c9d75 100644 --- a/lib/Transforms/Utils/Local.cpp +++ b/lib/Transforms/Utils/Local.cpp @@ -403,9 +403,22 @@ bool llvm::wouldInstructionBeTriviallyDead(Instruction *I, II->getIntrinsicID() == Intrinsic::launder_invariant_group) return true; - // Lifetime intrinsics are dead when their right-hand is undef. - if (II->isLifetimeStartOrEnd()) - return isa(II->getArgOperand(1)); + if (II->isLifetimeStartOrEnd()) { + auto *Arg = II->getArgOperand(1); + // Lifetime intrinsics are dead when their right-hand is undef. + if (isa(Arg)) + return true; + // If the right-hand is an alloc, global, or argument and the only uses + // are lifetime intrinsics then the intrinsics are dead. + if (isa(Arg) || isa(Arg) || isa(Arg)) + return llvm::all_of(Arg->uses(), [](Use &Use) { + if (IntrinsicInst *IntrinsicUse = + dyn_cast(Use.getUser())) + return IntrinsicUse->isLifetimeStartOrEnd(); + return false; + }); + return false; + } // Assumptions are dead if their condition is trivially true. Guards on // true are operationally no-ops. In the future we can consider more diff --git a/test/Analysis/BasicAA/modref.ll b/test/Analysis/BasicAA/modref.ll index a364a81a4e0..eb18f913fb9 100644 --- a/test/Analysis/BasicAA/modref.ll +++ b/test/Analysis/BasicAA/modref.ll @@ -80,7 +80,6 @@ define void @test3a(i8* %P, i8 %X) { %P2 = getelementptr i8, i8* %P, i32 2 store i8 %Y, i8* %P2 -; CHECK-NEXT: call void @llvm.lifetime.end call void @llvm.lifetime.end.p0i8(i64 10, i8* %P) ret void ; CHECK-NEXT: ret void diff --git a/test/Transforms/Attributor/memory_locations.ll b/test/Transforms/Attributor/memory_locations.ll index 1f0983047f7..6ca5cddd94d 100644 --- a/test/Transforms/Attributor/memory_locations.ll +++ b/test/Transforms/Attributor/memory_locations.ll @@ -386,11 +386,11 @@ define void @callerD2() { store i8 0, i8* %unknown ret void } -; CHECK: Function Attrs: argmemonly nounwind willreturn + +; CHECK: Function Attrs: nofree {{(norecurse )?}}nosync nounwind readnone willreturn define void @callerE(i8* %arg) { ; CHECK-LABEL: define {{[^@]+}}@callerE -; CHECK-SAME: (i8* nocapture [[ARG:%.*]]) -; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 4, i8* nocapture [[ARG]]) +; CHECK-SAME: (i8* nocapture nofree readnone [[ARG:%.*]]) ; CHECK-NEXT: ret void ; call void @llvm.lifetime.start.p0i8(i64 4, i8* %arg) diff --git a/test/Transforms/DCE/basic.ll b/test/Transforms/DCE/basic.ll index 6282ac78e75..0f70300ec0f 100644 --- a/test/Transforms/DCE/basic.ll +++ b/test/Transforms/DCE/basic.ll @@ -11,5 +11,63 @@ define void @test() { ret void } +declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) nounwind +declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture) nounwind + +; CHECK-LABEL: @test_lifetime_alloca +define i32 @test_lifetime_alloca() { +; Check that lifetime intrinsics are removed along with the pointer. +; CHECK-NEXT: @llvm.dbg.value +; CHECK-NEXT: ret i32 0 +; CHECK-NOT: llvm.lifetime.start +; CHECK-NOT: llvm.lifetime.end + %i = alloca i8, align 4 + call void @llvm.lifetime.start.p0i8(i64 -1, i8* %i) + call void @llvm.lifetime.end.p0i8(i64 -1, i8* %i) + ret i32 0 +} + +; CHECK-LABEL: @test_lifetime_arg +define i32 @test_lifetime_arg(i8*) { +; Check that lifetime intrinsics are removed along with the pointer. +; CHECK-NEXT: llvm.dbg.value +; CHECK-NEXT: ret i32 0 +; CHECK-NOT: llvm.lifetime.start +; CHECK-NOT: llvm.lifetime.end + call void @llvm.lifetime.start.p0i8(i64 -1, i8* %0) + call void @llvm.lifetime.end.p0i8(i64 -1, i8* %0) + ret i32 0 +} + +@glob = global i8 1 + +; CHECK-LABEL: @test_lifetime_global +define i32 @test_lifetime_global() { +; Check that lifetime intrinsics are removed along with the pointer. +; CHECK-NEXT: llvm.dbg.value +; CHECK-NEXT: ret i32 0 +; CHECK-NOT: llvm.lifetime.start +; CHECK-NOT: llvm.lifetime.end + call void @llvm.lifetime.start.p0i8(i64 -1, i8* @glob) + call void @llvm.lifetime.end.p0i8(i64 -1, i8* @glob) + ret i32 0 +} + +; CHECK-LABEL: @test_lifetime_bitcast +define i32 @test_lifetime_bitcast(i32*) { +; Check that lifetime intrinsics are NOT removed when the pointer is a bitcast. +; It's not uncommon for two bitcasts to be made: one for lifetime, one for use. +; TODO: Support the above case. +; CHECK-NEXT: bitcast +; CHECK-NEXT: llvm.dbg.value +; CHECK-NEXT: llvm.lifetime.start +; CHECK-NEXT: llvm.lifetime.end +; CHECK-NEXT: ret i32 0 + %2 = bitcast i32* %0 to i8* + call void @llvm.lifetime.start.p0i8(i64 -1, i8* %2) + call void @llvm.lifetime.end.p0i8(i64 -1, i8* %2) + ret i32 0 +} + ; CHECK: [[add]] = !DILocalVariable ; CHECK: [[sub]] = !DILocalVariable diff --git a/test/Transforms/DeadStoreElimination/lifetime.ll b/test/Transforms/DeadStoreElimination/lifetime.ll index 28a164cd8b5..c0cc2109c20 100644 --- a/test/Transforms/DeadStoreElimination/lifetime.ll +++ b/test/Transforms/DeadStoreElimination/lifetime.ll @@ -12,7 +12,7 @@ define void @test1() { store i8 0, i8* %A ;; Written to by memset call void @llvm.lifetime.end.p0i8(i64 1, i8* %A) -; CHECK: lifetime.end +; CHECK-NOT: lifetime.end call void @llvm.memset.p0i8.i8(i8* %A, i8 0, i8 -1, i1 false) ; CHECK-NOT: memset @@ -26,11 +26,9 @@ define void @test2(i32* %P) { %Q = getelementptr i32, i32* %P, i32 1 %R = bitcast i32* %Q to i8* call void @llvm.lifetime.start.p0i8(i64 4, i8* %R) -; CHECK: lifetime.start store i32 0, i32* %Q ;; This store is dead. ; CHECK-NOT: store call void @llvm.lifetime.end.p0i8(i64 4, i8* %R) -; CHECK: lifetime.end ret void } diff --git a/test/Transforms/InstCombine/vararg.ll b/test/Transforms/InstCombine/vararg.ll index 8fc9aafcdef..dd605fcc5c4 100644 --- a/test/Transforms/InstCombine/vararg.ll +++ b/test/Transforms/InstCombine/vararg.ll @@ -1,4 +1,4 @@ -; RUN: opt < %s -instcombine -instcombine-infinite-loop-threshold=2 -S | FileCheck %s +; RUN: opt < %s -instcombine -instcombine-infinite-loop-threshold=3 -S | FileCheck %s %struct.__va_list = type { i8*, i8*, i8*, i32, i32 }