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llvm-project/llvm/test/Transforms/MemCpyOpt/stack-move-offset.ll
Jameson Nash bc8302d52b Reapply "[MemCpyOpt] support offset slices for performStackMoveOptzn and processMemCpy" (#180002) 
In particular, support offset of src, since offset of dest will be a
followup change when dest is allowed to be not full-sized with copy.

Extracted from https://github.com/llvm/llvm-project/pull/150792

The miscomputation in the original version was due to incorrect
checking for ModRef, causing incorrect elimination of temporary
buffers: When checking for clobbering stores in performStackMoveOptzn,
use SrcPtr instead of SrcAlloca for the MemoryLocation. When SrcPtr is
offset into the alloca, but DstPtr is still not offset, we need to
check the actual copied region [SrcPtr, SrcPtr+Size) rather than
[SrcAlloca, SrcAlloca+Size) for ModRef. This check can become more
complex once DstOffset is non-zero or not-full-sized, as indicated in
the code comments.

Fixes https://github.com/llvm/llvm-project/issues/177185
Reverts https://github.com/llvm/llvm-project/pull/177482
Relands https://github.com/llvm/llvm-project/pull/176436

Co-authored-by: Gabriel Baraldi <baraldigabriel@gmail.com>
2026-02-24 09:33:16 -05:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
; RUN: opt < %s -passes=memcpyopt -verify-memoryssa -S | FileCheck %s
; Test that stack-move optimization works when src is a GEP into an alloca.
; For the optimization to trigger:
; - The copy must cover the entire dest alloca (Size == DestSize, DestOffset == 0)
; - SrcOffset must be a multiple of DestAlloca's alignment
; - SrcOffset must be non-negative
declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg)
declare void @llvm.lifetime.start.p0(ptr nocapture)
declare void @llvm.lifetime.end.p0(ptr nocapture)
declare void @use_nocapture(ptr nocapture)
; Basic test: memcpy from GEP(src) to dest alloca
; src = [16 x i8], dest = [8 x i8] align 8, copy 8 bytes
; SrcOffset(8) is a multiple of DestAlign(8), so optimization applies.
; After optimization: dest uses become src+8
define void @memcpy_src_gep_to_dest_alloca() {
; CHECK-LABEL: define void @memcpy_src_gep_to_dest_alloca() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [16 x i8], align 8
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 8
; CHECK-NEXT: [[SRC_GEP1:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 8
; CHECK-NEXT: store i64 42, ptr [[SRC_GEP1]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP1]])
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP]])
; CHECK-NEXT: ret void
;
%src = alloca [16 x i8], align 4
%dest = alloca [8 x i8], align 8
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
%src.gep = getelementptr inbounds i8, ptr %src, i64 8
store i64 42, ptr %src.gep
call void @use_nocapture(ptr nocapture %src.gep)
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %dest, ptr align 8 %src.gep, i64 8, i1 false)
call void @use_nocapture(ptr nocapture %dest)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Test: memcpy from GEP(src) to dest alloca with different offset
; src = [12 x i8], dest = [8 x i8] align 4, copy 8 bytes from src+4
; SrcOffset(4) is a multiple of DestAlign(4), so optimization applies.
; After optimization: dest uses become src+4
define void @memcpy_src_gep_offset4_to_dest_alloca() {
; CHECK-LABEL: define void @memcpy_src_gep_offset4_to_dest_alloca() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [12 x i8], align 4
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 4
; CHECK-NEXT: [[SRC_GEP1:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 4
; CHECK-NEXT: store i64 42, ptr [[SRC_GEP1]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP1]])
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP]])
; CHECK-NEXT: ret void
;
%src = alloca [12 x i8], align 4
%dest = alloca [8 x i8], align 4
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
%src.gep = getelementptr inbounds i8, ptr %src, i64 4
store i64 42, ptr %src.gep
call void @use_nocapture(ptr nocapture %src.gep)
call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dest, ptr align 4 %src.gep, i64 8, i1 false)
call void @use_nocapture(ptr nocapture %dest)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Test: load/store from GEP(src) to dest alloca
; src = [8 x i8], dest = [4 x i8] align 4, load/store 4 bytes from src+4
; SrcOffset(4) is a multiple of DestAlign(4), so optimization applies.
define void @load_store_src_gep_to_dest_alloca() {
; CHECK-LABEL: define void @load_store_src_gep_to_dest_alloca() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [8 x i8], align 4
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 4
; CHECK-NEXT: [[SRC_GEP1:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 4
; CHECK-NEXT: store i32 42, ptr [[SRC_GEP1]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP1]])
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP]])
; CHECK-NEXT: ret void
;
%src = alloca [8 x i8], align 4
%dest = alloca [4 x i8], align 4
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
%src.gep = getelementptr inbounds i8, ptr %src, i64 4
store i32 42, ptr %src.gep
call void @use_nocapture(ptr nocapture %src.gep)
%val = load i32, ptr %src.gep
store i32 %val, ptr %dest
call void @use_nocapture(ptr nocapture %dest)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Test: both src and dest are direct allocas (no offset), same size
; This is the basic stack-move case, included here for completeness.
define void @memcpy_both_direct_allocas() {
; CHECK-LABEL: define void @memcpy_both_direct_allocas() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [8 x i8], align 8
; CHECK-NEXT: store i64 42, ptr [[SRC]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC]])
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC]])
; CHECK-NEXT: ret void
;
%src = alloca [8 x i8], align 4
%dest = alloca [8 x i8], align 8
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
store i64 42, ptr %src
call void @use_nocapture(ptr nocapture %src)
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %dest, ptr align 4 %src, i64 8, i1 false)
call void @use_nocapture(ptr nocapture %dest)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Negative test: dest has offset (dest is GEP, not direct alloca)
; The optimization requires DestOffset == 0.
define void @no_optimize_dest_has_offset() {
; CHECK-LABEL: define void @no_optimize_dest_has_offset() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [16 x i8], align 4
; CHECK-NEXT: [[DEST:%.*]] = alloca [16 x i8], align 8
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[SRC]])
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[DEST]])
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 8
; CHECK-NEXT: [[DEST_GEP:%.*]] = getelementptr inbounds i8, ptr [[DEST]], i64 8
; CHECK-NEXT: store i64 42, ptr [[SRC_GEP]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP]])
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[DEST_GEP]], ptr align 4 [[SRC_GEP]], i64 8, i1 false)
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[DEST_GEP]])
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[SRC]])
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[DEST]])
; CHECK-NEXT: ret void
;
%src = alloca [16 x i8], align 4
%dest = alloca [16 x i8], align 8
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
%src.gep = getelementptr inbounds i8, ptr %src, i64 8
%dest.gep = getelementptr inbounds i8, ptr %dest, i64 8
store i64 42, ptr %src.gep
call void @use_nocapture(ptr nocapture %src.gep)
call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dest.gep, ptr align 4 %src.gep, i64 8, i1 false)
call void @use_nocapture(ptr nocapture %dest.gep)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Negative test: copy doesn't cover entire dest alloca (Size != DestSize)
; src = [12 x i8], dest = [16 x i8], copy only 8 bytes
define void @no_optimize_partial_dest_copy() {
; CHECK-LABEL: define void @no_optimize_partial_dest_copy() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [12 x i8], align 4
; CHECK-NEXT: [[DEST:%.*]] = alloca [16 x i8], align 4
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[SRC]])
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[DEST]])
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 4
; CHECK-NEXT: store i64 42, ptr [[SRC_GEP]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP]])
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[DEST]], ptr align 4 [[SRC_GEP]], i64 8, i1 false)
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[DEST]])
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[SRC]])
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[DEST]])
; CHECK-NEXT: ret void
;
%src = alloca [12 x i8], align 4
%dest = alloca [16 x i8], align 4
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
%src.gep = getelementptr inbounds i8, ptr %src, i64 4
store i64 42, ptr %src.gep
call void @use_nocapture(ptr nocapture %src.gep)
call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dest, ptr align 4 %src.gep, i64 8, i1 false)
call void @use_nocapture(ptr nocapture %dest)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Negative test: SrcOffset not a multiple of DestAlign
; src = [12 x i8] with offset 4, dest = [8 x i8] align 8
; SrcOffset(4) % DestAlign(8) = 4 != 0 -> rejected
define void @no_optimize_alignment_mismatch() {
; CHECK-LABEL: define void @no_optimize_alignment_mismatch() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [12 x i8], align 4
; CHECK-NEXT: [[DEST:%.*]] = alloca [8 x i8], align 8
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[SRC]])
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[DEST]])
; CHECK-NEXT: [[SRC_GEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i64 4
; CHECK-NEXT: store i64 42, ptr [[SRC_GEP]], align 4
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[SRC_GEP]])
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 [[DEST]], ptr align 4 [[SRC_GEP]], i64 8, i1 false)
; CHECK-NEXT: call void @use_nocapture(ptr captures(none) [[DEST]])
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[SRC]])
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[DEST]])
; CHECK-NEXT: ret void
;
%src = alloca [12 x i8], align 4
%dest = alloca [8 x i8], align 8
call void @llvm.lifetime.start.p0(ptr %src)
call void @llvm.lifetime.start.p0(ptr %dest)
%src.gep = getelementptr inbounds i8, ptr %src, i64 4
store i64 42, ptr %src.gep
call void @use_nocapture(ptr nocapture %src.gep)
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %dest, ptr align 4 %src.gep, i64 8, i1 false)
call void @use_nocapture(ptr nocapture %dest)
call void @llvm.lifetime.end.p0(ptr %src)
call void @llvm.lifetime.end.p0(ptr %dest)
ret void
}
; Negative test: Clobbering store to source offset between memcpy from source and memcpy to dest
; This is a minimal reproducer for the bug in LLVM PR #176436.
define void @no_optimize_clobbering_store_to_src_offset(ptr noalias %dst) {
; CHECK-LABEL: define void @no_optimize_clobbering_store_to_src_offset
; CHECK-SAME: (ptr noalias [[DST:%.*]]) {
; CHECK-NEXT: [[TEMP2:%.*]] = alloca { i64, i64 }, align 8
; CHECK-NEXT: [[TEMP1:%.*]] = alloca { i64, i64 }, align 8
; CHECK-NEXT: [[LOCAL:%.*]] = alloca { [48 x i8], { i64, i64 }, ptr }, align 8
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[TEMP1]])
; CHECK-NEXT: [[DST_BUF:%.*]] = getelementptr i8, ptr [[DST]], i64 48
; CHECK-NEXT: [[LOCAL_BUF:%.*]] = getelementptr inbounds i8, ptr [[LOCAL]], i64 48
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 [[LOCAL_BUF]], ptr align 8 [[DST_BUF]], i64 16, i1 false)
; CHECK-NEXT: store i8 0, ptr [[DST_BUF]], align 1
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[TEMP1]])
; CHECK-NEXT: call void @llvm.lifetime.start.p0(ptr [[TEMP2]])
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 [[TEMP2]], ptr align 8 [[LOCAL_BUF]], i64 16, i1 false)
; CHECK-NEXT: store i8 0, ptr [[LOCAL_BUF]], align 1
; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 [[DST_BUF]], ptr align 8 [[TEMP2]], i64 16, i1 false)
; CHECK-NEXT: call void @llvm.lifetime.end.p0(ptr [[TEMP2]])
; CHECK-NEXT: ret void
;
%temp2 = alloca { i64, i64 }, align 8
%temp1 = alloca { i64, i64 }, align 8
%local = alloca { [48 x i8], { i64, i64 }, ptr }, align 8
; First move: copy from dst+48 to local+48 via temp1
call void @llvm.lifetime.start.p0(ptr %temp1)
%dst_buf = getelementptr i8, ptr %dst, i64 48
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %temp1, ptr align 8 %dst_buf, i64 16, i1 false)
store i8 0, ptr %dst_buf, align 1
%local_buf = getelementptr inbounds i8, ptr %local, i64 48
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %local_buf, ptr align 8 %temp1, i64 16, i1 false)
call void @llvm.lifetime.end.p0(ptr %temp1)
; Second move: copy from local+48 back to dst+48 via temp2
; BUG: PR incorrectly eliminated temp2 but the store below clobbers part of local_buf first!
; The fix ensures we check the right portion of SrcAlloca for any clobbering.
call void @llvm.lifetime.start.p0(ptr %temp2)
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %temp2, ptr align 8 %local_buf, i64 16, i1 false)
store i8 0, ptr %local_buf, align 1 ; <-- clobbers byte 48 of %local
call void @llvm.memcpy.p0.p0.i64(ptr align 8 %dst_buf, ptr align 8 %temp2, i64 16, i1 false)
call void @llvm.lifetime.end.p0(ptr %temp2)
ret void
}
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