[llvm] [LoopVersioningLICM] Only mark pointers with generated checks as noalias (PR #135168)
John Brawn via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 10 05:03:44 PDT 2025
https://github.com/john-brawn-arm created https://github.com/llvm/llvm-project/pull/135168
Currently when we version a loop all loads and stores have the noalias metadata added to them. If there were some pointers that could not be analysed, and thus we could not generate runtime aliasing checks for, then we should not mark loads and stores using these pointers as noalias.
Currently this does nothing, as LoopAccessAnalysis discards all results if it couldn't analyse every pointer leading to no loop versioning happening, but an upcoming patch will change that and we need this first otherwise we incorrectly mark some pointers as noalias even when they aren't.
>From 8bbcb5d05ad042675bf4f41b3d4e01bfec7a28b6 Mon Sep 17 00:00:00 2001
From: John Brawn <john.brawn at arm.com>
Date: Tue, 1 Apr 2025 16:55:01 +0100
Subject: [PATCH] [LoopVersioningLICM] Only mark pointers with generated checks
as noalias
Currently when we version a loop all loads and stores have the noalias
metadata added to them. If there were some pointers that could not be
analyzed, and thus we could not generate runtime aliasing checks for,
then we should not mark loads and stores using these pointers as
noalias.
Currently this does nothing, as LoopAccessAnalysis discards all
results if it couldn't analyse every pointer leading to no loop
ersioning happening, but an upcoming patch will change that and we
need this first otherwise we incorrectly mark some pointers as noalias
even when they aren't.
---
.../Transforms/Scalar/LoopVersioningLICM.cpp | 30 +-
.../load-from-unknown-address.ll | 307 ++++++++++++++++++
2 files changed, 327 insertions(+), 10 deletions(-)
create mode 100644 llvm/test/Transforms/LoopVersioningLICM/load-from-unknown-address.ll
diff --git a/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp b/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp
index 6e91c4fa6e230..74b424655a9fa 100644
--- a/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopVersioningLICM.cpp
@@ -344,6 +344,13 @@ bool LoopVersioningLICM::instructionSafeForVersioning(Instruction *I) {
}
LoadAndStoreCounter++;
Value *Ptr = St->getPointerOperand();
+ // Don't allow stores that we don't have runtime checks for, as we won't be
+ // able to mark them noalias meaning they would prevent any code motion.
+ auto &Pointers = LAI->getRuntimePointerChecking()->Pointers;
+ if (!any_of(Pointers, [&](auto &P) { return P.PointerValue == Ptr; })) {
+ LLVM_DEBUG(dbgs() << " Found a store without a runtime check.\n");
+ return false;
+ }
// Check loop invariant.
if (SE->isLoopInvariant(SE->getSCEV(Ptr), CurLoop))
InvariantCounter++;
@@ -361,6 +368,13 @@ bool LoopVersioningLICM::legalLoopInstructions() {
InvariantCounter = 0;
IsReadOnlyLoop = true;
using namespace ore;
+ // Get LoopAccessInfo from current loop via the proxy.
+ LAI = &LAIs.getInfo(*CurLoop);
+ // Check LoopAccessInfo for need of runtime check.
+ if (LAI->getRuntimePointerChecking()->getChecks().empty()) {
+ LLVM_DEBUG(dbgs() << " LAA: Runtime check not found !!\n");
+ return false;
+ }
// Iterate over loop blocks and instructions of each block and check
// instruction safety.
for (auto *Block : CurLoop->getBlocks())
@@ -374,13 +388,6 @@ bool LoopVersioningLICM::legalLoopInstructions() {
return false;
}
}
- // Get LoopAccessInfo from current loop via the proxy.
- LAI = &LAIs.getInfo(*CurLoop);
- // Check LoopAccessInfo for need of runtime check.
- if (LAI->getRuntimePointerChecking()->getChecks().empty()) {
- LLVM_DEBUG(dbgs() << " LAA: Runtime check not found !!\n");
- return false;
- }
// Number of runtime-checks should be less then RuntimeMemoryCheckThreshold
if (LAI->getNumRuntimePointerChecks() >
VectorizerParams::RuntimeMemoryCheckThreshold) {
@@ -515,13 +522,16 @@ void LoopVersioningLICM::setNoAliasToLoop(Loop *VerLoop) {
StringRef Name = "LVAliasScope";
MDNode *NewScope = MDB.createAnonymousAliasScope(NewDomain, Name);
SmallVector<Metadata *, 4> Scopes{NewScope}, NoAliases{NewScope};
+ auto &Pointers = LAI->getRuntimePointerChecking()->Pointers;
+
// Iterate over each instruction of loop.
// set no-alias for all load & store instructions.
for (auto *Block : CurLoop->getBlocks()) {
for (auto &Inst : *Block) {
- // Only interested in instruction that may modify or read memory.
- if (!Inst.mayReadFromMemory() && !Inst.mayWriteToMemory())
- continue;
+ // We can only add noalias to pointers that we've inserted checks for
+ Value *V = getLoadStorePointerOperand(&Inst);
+ if (!V || !any_of(Pointers, [&](auto &P) { return P.PointerValue == V; }))
+ continue;
// Set no-alias for current instruction.
Inst.setMetadata(
LLVMContext::MD_noalias,
diff --git a/llvm/test/Transforms/LoopVersioningLICM/load-from-unknown-address.ll b/llvm/test/Transforms/LoopVersioningLICM/load-from-unknown-address.ll
new file mode 100644
index 0000000000000..e9b2954039198
--- /dev/null
+++ b/llvm/test/Transforms/LoopVersioningLICM/load-from-unknown-address.ll
@@ -0,0 +1,307 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals none --version 5
+; RUN: opt < %s -S -passes='function(loop-versioning-licm,loop-mssa(licm))' | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
+
+; In these tests we have a loop where we can calculate the bounds of some memory
+; accesses but not others.
+
+; Load from a gep whose bounds can't be calculated as the offset is loaded from memory
+; FIXME: Not knowing the bounds of the gep shouldn't stop us from hoisting the load of rval
+define void @gep_loaded_offset(ptr %p, ptr %q, ptr %r, i32 %n) {
+; CHECK-LABEL: define void @gep_loaded_offset(
+; CHECK-SAME: ptr [[P:%.*]], ptr [[Q:%.*]], ptr [[R:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_ADDR:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[P_ADDR:%.*]] = phi ptr [ [[INCDEC_PTR:%.*]], %[[WHILE_BODY]] ], [ [[P]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_ADDR]], -1
+; CHECK-NEXT: [[RVAL:%.*]] = load i64, ptr [[R]], align 4
+; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[Q]], i64 [[RVAL]]
+; CHECK-NEXT: [[VAL:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[INCDEC_PTR]] = getelementptr inbounds nuw i8, ptr [[P_ADDR]], i64 4
+; CHECK-NEXT: store i32 [[VAL]], ptr [[P_ADDR]], align 4
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n.addr = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %p.addr = phi ptr [ %incdec.ptr, %while.body ], [ %p, %entry ]
+ %dec = add nsw i32 %n.addr, -1
+ %rval = load i64, ptr %r, align 4
+ %arrayidx = getelementptr inbounds i32, ptr %q, i64 %rval
+ %val = load i32, ptr %arrayidx, align 4
+ %incdec.ptr = getelementptr inbounds nuw i8, ptr %p.addr, i64 4
+ store i32 %val, ptr %p.addr, align 4
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
+
+; As above but with a store to the loaded address. This should prevent the loop
+; from being versioned, as we wouldn't be able to do any code motion.
+define void @gep_loaded_offset_with_store(ptr %p, ptr %q, ptr %r, i32 %n) {
+; CHECK-LABEL: define void @gep_loaded_offset_with_store(
+; CHECK-SAME: ptr [[P:%.*]], ptr [[Q:%.*]], ptr [[R:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_ADDR:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[P_ADDR:%.*]] = phi ptr [ [[INCDEC_PTR:%.*]], %[[WHILE_BODY]] ], [ [[P]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_ADDR]], -1
+; CHECK-NEXT: [[RVAL:%.*]] = load i64, ptr [[R]], align 4
+; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[Q]], i64 [[RVAL]]
+; CHECK-NEXT: [[VAL:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: store i32 0, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[INCDEC_PTR]] = getelementptr inbounds nuw i8, ptr [[P_ADDR]], i64 4
+; CHECK-NEXT: store i32 [[VAL]], ptr [[P_ADDR]], align 4
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n.addr = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %p.addr = phi ptr [ %incdec.ptr, %while.body ], [ %p, %entry ]
+ %dec = add nsw i32 %n.addr, -1
+ %rval = load i64, ptr %r, align 4
+ %arrayidx = getelementptr inbounds i32, ptr %q, i64 %rval
+ %val = load i32, ptr %arrayidx, align 4
+ store i32 0, ptr %arrayidx, align 4
+ %incdec.ptr = getelementptr inbounds nuw i8, ptr %p.addr, i64 4
+ store i32 %val, ptr %p.addr, align 4
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
+
+; Load from a gep whose bounds can't be calculated as the pointer is loaded from memory
+; FIXME: Not knowing the bounds of the gep shouldn't stop us from hoisting the load of rval
+define void @gep_loaded_base(ptr %p, ptr %q, ptr %r, i32 %n) {
+; CHECK-LABEL: define void @gep_loaded_base(
+; CHECK-SAME: ptr [[P:%.*]], ptr [[Q:%.*]], ptr [[R:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_ADDR:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[P_ADDR:%.*]] = phi ptr [ [[INCDEC_PTR:%.*]], %[[WHILE_BODY]] ], [ [[P]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_ADDR]], -1
+; CHECK-NEXT: [[RVAL:%.*]] = load ptr, ptr [[R]], align 4
+; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[RVAL]], i64 0
+; CHECK-NEXT: [[VAL:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[INCDEC_PTR]] = getelementptr inbounds nuw i8, ptr [[P_ADDR]], i64 4
+; CHECK-NEXT: store i32 [[VAL]], ptr [[P_ADDR]], align 4
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n.addr = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %p.addr = phi ptr [ %incdec.ptr, %while.body ], [ %p, %entry ]
+ %dec = add nsw i32 %n.addr, -1
+ %rval = load ptr, ptr %r, align 4
+ %arrayidx = getelementptr inbounds i32, ptr %rval, i64 0
+ %val = load i32, ptr %arrayidx, align 4
+ %incdec.ptr = getelementptr inbounds nuw i8, ptr %p.addr, i64 4
+ store i32 %val, ptr %p.addr, align 4
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
+
+; Load from a gep with an offset that scalar evolution can't describe
+; FIXME: Not knowing the bounds of the gep shouldn't stop us from hoisting the load of qval
+define void @gep_strange_offset(ptr %p, ptr %q, ptr %r, i32 %n) {
+; CHECK-LABEL: define void @gep_strange_offset(
+; CHECK-SAME: ptr [[P:%.*]], ptr [[Q:%.*]], ptr [[R:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_ADDR:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[P_ADDR:%.*]] = phi ptr [ [[INCDEC_PTR:%.*]], %[[WHILE_BODY]] ], [ [[P]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_ADDR]], -1
+; CHECK-NEXT: [[QVAL:%.*]] = load i32, ptr [[Q]], align 4
+; CHECK-NEXT: [[REM:%.*]] = srem i32 [[DEC]], 2
+; CHECK-NEXT: [[IDXPROM:%.*]] = sext i32 [[REM]] to i64
+; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[R]], i64 [[IDXPROM]]
+; CHECK-NEXT: [[VAL:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT: [[ADD:%.*]] = add nsw i32 [[VAL]], [[QVAL]]
+; CHECK-NEXT: [[INCDEC_PTR]] = getelementptr inbounds nuw i8, ptr [[P_ADDR]], i64 4
+; CHECK-NEXT: store i32 [[ADD]], ptr [[P_ADDR]], align 4
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n.addr = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %p.addr = phi ptr [ %incdec.ptr, %while.body ], [ %p, %entry ]
+ %dec = add nsw i32 %n.addr, -1
+ %qval = load i32, ptr %q, align 4
+ %rem = srem i32 %dec, 2
+ %idxprom = sext i32 %rem to i64
+ %arrayidx = getelementptr inbounds i32, ptr %r, i64 %idxprom
+ %val = load i32, ptr %arrayidx, align 4
+ %add = add nsw i32 %val, %qval
+ %incdec.ptr = getelementptr inbounds nuw i8, ptr %p.addr, i64 4
+ store i32 %add, ptr %p.addr, align 4
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
+
+; A memcpy-like loop where the source address is loaded from a pointer
+; FIXME: We should be able to hoist the load of the source address pointer
+define void @memcpy_load_src(ptr %dst, ptr %src, i32 %n) {
+; CHECK-LABEL: define void @memcpy_load_src(
+; CHECK-SAME: ptr [[DST:%.*]], ptr [[SRC:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_VAL:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DST_VAL:%.*]] = phi ptr [ [[DST_VAL_NEXT:%.*]], %[[WHILE_BODY]] ], [ [[DST]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_VAL]], -1
+; CHECK-NEXT: [[SRC_VAL:%.*]] = load ptr, ptr [[SRC]], align 8
+; CHECK-NEXT: [[SRC_VAL_NEXT:%.*]] = getelementptr inbounds nuw i8, ptr [[SRC_VAL]], i64 1
+; CHECK-NEXT: [[DST_VAL_NEXT]] = getelementptr inbounds nuw i8, ptr [[DST_VAL]], i64 1
+; CHECK-NEXT: store ptr [[SRC_VAL_NEXT]], ptr [[SRC]], align 8
+; CHECK-NEXT: [[VAL:%.*]] = load i8, ptr [[SRC_VAL]], align 1
+; CHECK-NEXT: store i8 [[VAL]], ptr [[DST_VAL]], align 1
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n_val = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %dst_val = phi ptr [ %dst_val.next, %while.body ], [ %dst, %entry ]
+ %dec = add nsw i32 %n_val, -1
+ %src_val = load ptr, ptr %src, align 8
+ %src_val.next = getelementptr inbounds nuw i8, ptr %src_val, i64 1
+ %dst_val.next = getelementptr inbounds nuw i8, ptr %dst_val, i64 1
+ store ptr %src_val.next, ptr %src, align 8
+ %val = load i8, ptr %src_val, align 1
+ store i8 %val, ptr %dst_val, align 1
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
+
+; A memcpy-like loop where the destination address is loaded from a pointer
+; FIXME: We could hoist the load of the destination address, but doing the
+; bounds check of the store through that pointer itself requires using the
+; hoisted load.
+define void @memcpy_load_dst(ptr %dst, ptr %src, i32 %n) {
+; CHECK-LABEL: define void @memcpy_load_dst(
+; CHECK-SAME: ptr [[DST:%.*]], ptr [[SRC:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_VAL:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[SRC_VAL:%.*]] = phi ptr [ [[SRC_VAL_NEXT:%.*]], %[[WHILE_BODY]] ], [ [[SRC]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_VAL]], -1
+; CHECK-NEXT: [[DST_VAL:%.*]] = load ptr, ptr [[DST]], align 8
+; CHECK-NEXT: [[SRC_VAL_NEXT]] = getelementptr inbounds nuw i8, ptr [[SRC_VAL]], i64 1
+; CHECK-NEXT: [[DST_VAL_NEXT:%.*]] = getelementptr inbounds nuw i8, ptr [[DST_VAL]], i64 1
+; CHECK-NEXT: store ptr [[DST_VAL_NEXT]], ptr [[DST]], align 8
+; CHECK-NEXT: [[VAL:%.*]] = load i8, ptr [[SRC_VAL]], align 1
+; CHECK-NEXT: store i8 [[VAL]], ptr [[DST_VAL]], align 1
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n_val = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %src_val = phi ptr [ %src_val.next, %while.body ], [ %src, %entry ]
+ %dec = add nsw i32 %n_val, -1
+ %dst_val = load ptr, ptr %dst, align 8
+ %src_val.next = getelementptr inbounds nuw i8, ptr %src_val, i64 1
+ %dst_val.next = getelementptr inbounds nuw i8, ptr %dst_val, i64 1
+ store ptr %dst_val.next, ptr %dst, align 8
+ %val = load i8, ptr %src_val, align 1
+ store i8 %val, ptr %dst_val, align 1
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
+
+; A memcpy-like loop where both the source and destination pointers are loaded from pointers
+; FIXME: We could hoist the loads of both addresses, but doing the bounds check
+; of the store through the destination address itself requires using the hoisted
+; load.
+define void @memcpy_load_src_dst(ptr %dst, ptr %src, i32 %n) {
+; CHECK-LABEL: define void @memcpy_load_src_dst(
+; CHECK-SAME: ptr [[DST:%.*]], ptr [[SRC:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[WHILE_BODY:.*]]
+; CHECK: [[WHILE_BODY]]:
+; CHECK-NEXT: [[N_VAL:%.*]] = phi i32 [ [[DEC:%.*]], %[[WHILE_BODY]] ], [ [[N]], %[[ENTRY]] ]
+; CHECK-NEXT: [[DEC]] = add nsw i32 [[N_VAL]], -1
+; CHECK-NEXT: [[SRC_VAL:%.*]] = load ptr, ptr [[SRC]], align 8
+; CHECK-NEXT: [[DST_VAL:%.*]] = load ptr, ptr [[DST]], align 8
+; CHECK-NEXT: [[SRC_VAL_NEXT:%.*]] = getelementptr inbounds nuw i8, ptr [[SRC_VAL]], i64 1
+; CHECK-NEXT: [[DST_VAL_NEXT:%.*]] = getelementptr inbounds nuw i8, ptr [[DST_VAL]], i64 1
+; CHECK-NEXT: store ptr [[SRC_VAL_NEXT]], ptr [[SRC]], align 8
+; CHECK-NEXT: store ptr [[DST_VAL_NEXT]], ptr [[DST]], align 8
+; CHECK-NEXT: [[VAL:%.*]] = load i8, ptr [[SRC_VAL]], align 1
+; CHECK-NEXT: store i8 [[VAL]], ptr [[DST_VAL]], align 1
+; CHECK-NEXT: [[TOBOOL_NOT:%.*]] = icmp eq i32 [[DEC]], 0
+; CHECK-NEXT: br i1 [[TOBOOL_NOT]], label %[[WHILE_END:.*]], label %[[WHILE_BODY]]
+; CHECK: [[WHILE_END]]:
+; CHECK-NEXT: ret void
+;
+entry:
+ br label %while.body
+
+while.body:
+ %n_val = phi i32 [ %dec, %while.body ], [ %n, %entry ]
+ %dec = add nsw i32 %n_val, -1
+ %src_val = load ptr, ptr %src, align 8
+ %dst_val = load ptr, ptr %dst, align 8
+ %src_val.next = getelementptr inbounds nuw i8, ptr %src_val, i64 1
+ %dst_val.next = getelementptr inbounds nuw i8, ptr %dst_val, i64 1
+ store ptr %src_val.next, ptr %src, align 8
+ store ptr %dst_val.next, ptr %dst, align 8
+ %val = load i8, ptr %src_val, align 1
+ store i8 %val, ptr %dst_val, align 1
+ %tobool.not = icmp eq i32 %dec, 0
+ br i1 %tobool.not, label %while.end, label %while.body
+
+while.end:
+ ret void
+}
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