[llvm] [MemCpyOpt] No need to create `memcpy(a <- a)` (PR #98321)
via llvm-commits
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Wed Jul 10 06:56:56 PDT 2024
https://github.com/DianQK created https://github.com/llvm/llvm-project/pull/98321
When forwarding `memcpy`, we don't need to create `memcpy(a, a)`.
>From 4e61f5d6b69d8a64c50f1bfd3864b88635dc1ff7 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Wed, 10 Jul 2024 21:19:51 +0800
Subject: [PATCH 1/2] Pre-commit test cases
---
llvm/test/Transforms/MemCpyOpt/memcpy.ll | 54 ++++++++++++++++++++++++
1 file changed, 54 insertions(+)
diff --git a/llvm/test/Transforms/MemCpyOpt/memcpy.ll b/llvm/test/Transforms/MemCpyOpt/memcpy.ll
index 48698f25174e7..22faff1fdd1ae 100644
--- a/llvm/test/Transforms/MemCpyOpt/memcpy.ll
+++ b/llvm/test/Transforms/MemCpyOpt/memcpy.ll
@@ -139,6 +139,60 @@ define void @test6_memcpy(ptr %src, ptr %dest) nounwind {
ret void
}
+; FIXME: When forwarding to memcpy(arg+1, arg+1), we don't need to create this memcpy.
+define void @test6_memcpy_forward_back(ptr %arg) nounwind {
+; CHECK-LABEL: @test6_memcpy_forward_back(
+; CHECK-NEXT: [[TMP:%.*]] = alloca [16 x i8], align 1
+; CHECK-NEXT: [[SRC:%.*]] = getelementptr inbounds i8, ptr [[ARG:%.*]], i64 1
+; CHECK-NEXT: [[DEST:%.*]] = getelementptr inbounds i8, ptr [[ARG]], i64 1
+; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[TMP]], ptr align 1 [[SRC]], i32 16, i1 false)
+; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[DEST]], ptr align 1 [[TMP]], i32 16, i1 false)
+; CHECK-NEXT: ret void
+;
+ %tmp = alloca [16 x i8], align 1
+ %src = getelementptr inbounds i8, ptr %arg, i64 1
+ %dest = getelementptr inbounds i8, ptr %arg, i64 1
+ call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 %tmp, ptr align 1 %src, i32 16, i1 false)
+ call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 %dest, ptr align 1 %tmp, i32 16, i1 false)
+ ret void
+}
+
+; We have to retain this `memcpy(arg+2, arg+1)` forwarding.
+define void @test6_memcpy_forward_not_back(ptr %arg) nounwind {
+; CHECK-LABEL: @test6_memcpy_forward_not_back(
+; CHECK-NEXT: [[TMP:%.*]] = alloca [16 x i8], align 1
+; CHECK-NEXT: [[SRC:%.*]] = getelementptr inbounds i8, ptr [[ARG:%.*]], i64 1
+; CHECK-NEXT: [[DEST:%.*]] = getelementptr inbounds i8, ptr [[ARG]], i64 2
+; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[TMP]], ptr align 1 [[SRC]], i32 16, i1 false)
+; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[DEST]], ptr align 1 [[TMP]], i32 16, i1 false)
+; CHECK-NEXT: ret void
+;
+ %tmp = alloca [16 x i8], align 1
+ %src = getelementptr inbounds i8, ptr %arg, i64 1
+ %dest = getelementptr inbounds i8, ptr %arg, i64 2
+ call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 %tmp, ptr align 1 %src, i32 16, i1 false)
+ call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 %dest, ptr align 1 %tmp, i32 16, i1 false)
+ ret void
+}
+
+; There is data writing between the two memcpy operations.
+define void @test6_memcpy_forward_back_failed(ptr %arg) nounwind {
+; CHECK-LABEL: @test6_memcpy_forward_back_failed(
+; CHECK-NEXT: [[TMP:%.*]] = alloca [16 x i8], align 1
+; CHECK-NEXT: [[SRC:%.*]] = getelementptr inbounds i8, ptr [[ARG:%.*]], i64 1
+; CHECK-NEXT: [[DEST:%.*]] = getelementptr inbounds i8, ptr [[ARG]], i64 1
+; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[TMP]], ptr align 1 [[SRC]], i32 16, i1 false)
+; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[DEST]], ptr align 1 [[TMP]], i32 16, i1 false)
+; CHECK-NEXT: ret void
+;
+ %tmp = alloca [16 x i8], align 1
+ %src = getelementptr inbounds i8, ptr %arg, i64 1
+ %dest = getelementptr inbounds i8, ptr %arg, i64 1
+ call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 %tmp, ptr align 1 %src, i32 16, i1 false)
+ store i8 1, ptr %dest, align 1
+ call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 %dest, ptr align 1 %tmp, i32 16, i1 false)
+ ret void
+}
@x = external global %0
>From ec1ab1cd3cfb7e9775bdbc8294d9522832a68de8 Mon Sep 17 00:00:00 2001
From: DianQK <dianqk at dianqk.net>
Date: Wed, 10 Jul 2024 13:47:07 +0800
Subject: [PATCH 2/2] [MemCpyOpt] No need to create `memcpy(a <- a)`
---
llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp | 8 ++++++++
llvm/test/Transforms/MemCpyOpt/memcpy.ll | 6 +-----
2 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index b9efd9aaa28c5..1a4b3657cedae 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1161,6 +1161,14 @@ bool MemCpyOptPass::processMemCpyMemCpyDependence(MemCpyInst *M,
MSSA->getMemoryAccess(MDep), MSSA->getMemoryAccess(M)))
return false;
+ // No need to create `memcpy(a <- a)`.
+ if (BAA.isMustAlias(M->getDest(), MDep->getRawSource())) {
+ // Remove the instruction we're replacing.
+ eraseInstruction(M);
+ ++NumMemCpyInstr;
+ return true;
+ }
+
// If the dest of the second might alias the source of the first, then the
// source and dest might overlap. In addition, if the source of the first
// points to constant memory, they won't overlap by definition. Otherwise, we
diff --git a/llvm/test/Transforms/MemCpyOpt/memcpy.ll b/llvm/test/Transforms/MemCpyOpt/memcpy.ll
index 22faff1fdd1ae..a19cfe6e75b70 100644
--- a/llvm/test/Transforms/MemCpyOpt/memcpy.ll
+++ b/llvm/test/Transforms/MemCpyOpt/memcpy.ll
@@ -142,11 +142,7 @@ define void @test6_memcpy(ptr %src, ptr %dest) nounwind {
; FIXME: When forwarding to memcpy(arg+1, arg+1), we don't need to create this memcpy.
define void @test6_memcpy_forward_back(ptr %arg) nounwind {
; CHECK-LABEL: @test6_memcpy_forward_back(
-; CHECK-NEXT: [[TMP:%.*]] = alloca [16 x i8], align 1
-; CHECK-NEXT: [[SRC:%.*]] = getelementptr inbounds i8, ptr [[ARG:%.*]], i64 1
-; CHECK-NEXT: [[DEST:%.*]] = getelementptr inbounds i8, ptr [[ARG]], i64 1
-; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[TMP]], ptr align 1 [[SRC]], i32 16, i1 false)
-; CHECK-NEXT: call void @llvm.memcpy.inline.p0.p0.i32(ptr align 1 [[DEST]], ptr align 1 [[TMP]], i32 16, i1 false)
+; CHECK-NEXT: [[DEST:%.*]] = getelementptr inbounds i8, ptr [[ARG:%.*]], i64 1
; CHECK-NEXT: ret void
;
%tmp = alloca [16 x i8], align 1
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