[llvm] [MemCpyOpt] move SrcAlloca to the entry if transformation is performed (PR #67226)
Kohei Asano via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 25 01:24:46 PDT 2023
https://github.com/khei4 updated https://github.com/llvm/llvm-project/pull/67226
>From 5bde6fa98da40ea6fded2a8a790cf313fdd979c3 Mon Sep 17 00:00:00 2001
From: khei4 <kk.asano.luxy at gmail.com>
Date: Sun, 24 Sep 2023 01:20:25 +0900
Subject: [PATCH 1/2] [MemCpyOpt] move SrcAlloca to the entry if transformation
is performed
move test to the success zone
---
.../lib/Transforms/Scalar/MemCpyOptimizer.cpp | 22 +++++----
llvm/test/Transforms/MemCpyOpt/stack-move.ll | 47 ++++++++-----------
2 files changed, 32 insertions(+), 37 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index d87f2fb59814edf..44cfc80134ca18e 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1463,6 +1463,7 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
SmallVector<Instruction *, 4> LifetimeMarkers;
SmallSet<Instruction *, 4> NoAliasInstrs;
+ bool SrcNotDom = false;
// Recursively track the user and check whether modified alias exist.
auto IsDereferenceableOrNull = [](Value *V, const DataLayout &DL) -> bool {
@@ -1483,14 +1484,11 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
Worklist.pop_back();
for (const Use &U : I->uses()) {
auto *UI = cast<Instruction>(U.getUser());
- // TODO: We can perform the transformation if we move src alloca to
- // before the dominator of all uses. If any use that isn't dominated by
- // SrcAlloca exists, non-dominating uses will be produced.
- if (!DT->dominates(SrcAlloca, UI)) {
- LLVM_DEBUG(dbgs() << "Stack Move: SrcAlloca doesn't dominate all "
- "uses for the location, bailing\n");
- return false;
- }
+ // If any use that isn't dominated by SrcAlloca exists, we move src
+ // alloca to the entry before the transformation.
+ if (!DT->dominates(SrcAlloca, UI))
+ SrcNotDom = true;
+
if (Visited.size() >= MaxUsesToExplore) {
LLVM_DEBUG(
dbgs()
@@ -1600,7 +1598,13 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
if (!CaptureTrackingWithModRef(SrcAlloca, SrcModRefCallback))
return false;
- // We can do the transformation. First, align the allocas appropriately.
+ // We can do the transformation. First, move the SrcAlloca to the entry point
+ // if it's not dominator for all uses. After that SrcAlloca becomes the
+ // dominator, because it's in the entry BB.
+ if (SrcNotDom)
+ SrcAlloca->moveBefore(*SrcAlloca->getParent(),
+ SrcAlloca->getParent()->getFirstInsertionPt());
+ // Align the allocas appropriately.
SrcAlloca->setAlignment(
std::max(SrcAlloca->getAlign(), DestAlloca->getAlign()));
diff --git a/llvm/test/Transforms/MemCpyOpt/stack-move.ll b/llvm/test/Transforms/MemCpyOpt/stack-move.ll
index f6be486dce8ac1e..dee630f470d0053 100644
--- a/llvm/test/Transforms/MemCpyOpt/stack-move.ll
+++ b/llvm/test/Transforms/MemCpyOpt/stack-move.ll
@@ -45,6 +45,25 @@ define void @basic_memcpy() {
ret void
}
+define i32 @use_not_dominated_by_src_alloca() {
+; CHECK-LABEL: define i32 @use_not_dominated_by_src_alloca() {
+; CHECK-NEXT: [[SRC:%.*]] = alloca i8, align 4
+; CHECK-NEXT: [[DEST_GEP:%.*]] = getelementptr i64, ptr [[SRC]], i64 -1
+; CHECK-NEXT: [[DEST_USE:%.*]] = load i8, ptr [[DEST_GEP]], align 1
+; CHECK-NEXT: ret i32 0
+;
+ %dest = alloca i1, align 1
+ ; Replacing the use of dest with src causes no domination uses.
+ %dest.gep = getelementptr i64, ptr %dest, i64 -1
+ %dest.use = load i8, ptr %dest.gep, align 1
+ %src = alloca i8, align 4
+ %src.val = load i1, ptr %src, align 4
+
+ store i1 %src.val, ptr %dest, align 1
+
+ ret i32 0
+}
+
define void @basic_memmove() {
; CHECK-LABEL: define void @basic_memmove() {
; CHECK-NEXT: [[SRC:%.*]] = alloca [[STRUCT_FOO:%.*]], align 4
@@ -346,7 +365,6 @@ define void @avoid_memory_use_last_user_crash() {
ret void
}
-; TODO: if the last user is terminator, we won't insert lifetime.end.
; For multi-bb patch, we will insert it for next immediate post dominator block.
define void @terminator_lastuse() personality i32 0 {
; CHECK-LABEL: define void @terminator_lastuse() personality i32 0 {
@@ -718,7 +736,6 @@ unr2:
}
-; TODO: merge allocas for multi basicblock loop case.
define void @multi_bb_loop(i32 %n) {
; CHECK-LABEL: define void @multi_bb_loop
; CHECK-SAME: (i32 [[N:%.*]]) {
@@ -981,32 +998,6 @@ bb2:
; Optimization failures follow:
-; TODO: we can merge those alloca if we move src alloca to the start of the BB.
-; Tests that a the optimization isn't performed,
-; when any use that isn't dominated by SrcAlloca exists.
-define i32 @use_not_dominated_by_src_alloca() {
-; CHECK-LABEL: define i32 @use_not_dominated_by_src_alloca() {
-; CHECK-NEXT: [[DEST:%.*]] = alloca i1, align 1
-; CHECK-NEXT: [[DEST_GEP:%.*]] = getelementptr i64, ptr [[DEST]], i64 -1
-; CHECK-NEXT: [[DEST_USE:%.*]] = load i8, ptr [[DEST_GEP]], align 1
-; CHECK-NEXT: [[SRC:%.*]] = alloca i8, align 4
-; CHECK-NEXT: [[SRC_VAL:%.*]] = load i1, ptr [[SRC]], align 4
-; CHECK-NEXT: store i1 [[SRC_VAL]], ptr [[DEST]], align 1
-; CHECK-NEXT: ret i32 0
-;
- %dest = alloca i1, align 1
- ; Replacing the use of dest with src causes no domination uses.
- %dest.gep = getelementptr i64, ptr %dest, i64 -1
- %dest.use = load i8, ptr %dest.gep, align 1
- %src = alloca i8, align 4
- %src.val = load i1, ptr %src, align 4
-
- store i1 %src.val, ptr %dest, align 1
-
- ret i32 0
-}
-
-
; Tests that a memcpy that doesn't completely overwrite a stack value is a use
; for the purposes of liveness analysis, not a definition.
define void @incomplete_memcpy() {
>From 560f80d75f7e6f9bd67f8e14be435b1f0612942c Mon Sep 17 00:00:00 2001
From: Kohei Asano <32860920+khei4 at users.noreply.github.com>
Date: Mon, 25 Sep 2023 17:24:38 +0900
Subject: [PATCH 2/2] update: comments on the alloca move up
---
llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 44cfc80134ca18e..ccb8eadab48704f 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1598,9 +1598,7 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
if (!CaptureTrackingWithModRef(SrcAlloca, SrcModRefCallback))
return false;
- // We can do the transformation. First, move the SrcAlloca to the entry point
- // if it's not dominator for all uses. After that SrcAlloca becomes the
- // dominator, because it's in the entry BB.
+ // We can do the transformation. First, move the SrcAlloca to the start of the BB.
if (SrcNotDom)
SrcAlloca->moveBefore(*SrcAlloca->getParent(),
SrcAlloca->getParent()->getFirstInsertionPt());
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