[llvm] 4e89d11 - [InstCombine] Convert mem intrinsic with null into a noop (#100388)
via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 1 07:46:11 PDT 2024
Author: Yingwei Zheng
Date: 2024-08-01T22:46:07+08:00
New Revision: 4e89d1199c180fd384486ba2796368ec800180ee
URL: https://github.com/llvm/llvm-project/commit/4e89d1199c180fd384486ba2796368ec800180ee
DIFF: https://github.com/llvm/llvm-project/commit/4e89d1199c180fd384486ba2796368ec800180ee.diff
LOG: [InstCombine] Convert mem intrinsic with null into a noop (#100388)
When src/dest passed into memset/memcpy is null:
```
len == 0: this call is a noop.
len != 0: the behavior is undefined.
```
See also https://llvm.org/docs/LangRef.html#llvm-memset-intrinsics
Alive2: https://alive2.llvm.org/ce/z/tJeRNL
This patch converts these mem intrinsic calls into an assumption `len ==
0` to mitigate code-size bloat caused by JumpThreading.
Added:
llvm/test/Transforms/InstCombine/mem-intrinsics.ll
Modified:
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
llvm/test/Transforms/InstCombine/mempcpy.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index deb8e3cb6fabc..cc68fd4cf1c1b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1584,16 +1584,30 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
return eraseInstFromFunction(CI);
}
+ auto IsPointerUndefined = [MI](Value *Ptr) {
+ return isa<ConstantPointerNull>(Ptr) &&
+ !NullPointerIsDefined(
+ MI->getFunction(),
+ cast<PointerType>(Ptr->getType())->getAddressSpace());
+ };
+ bool SrcIsUndefined = false;
// If we can determine a pointer alignment that is bigger than currently
// set, update the alignment.
if (auto *MTI = dyn_cast<AnyMemTransferInst>(MI)) {
if (Instruction *I = SimplifyAnyMemTransfer(MTI))
return I;
+ SrcIsUndefined = IsPointerUndefined(MTI->getRawSource());
} else if (auto *MSI = dyn_cast<AnyMemSetInst>(MI)) {
if (Instruction *I = SimplifyAnyMemSet(MSI))
return I;
}
+ // If src/dest is null, this memory intrinsic must be a noop.
+ if (SrcIsUndefined || IsPointerUndefined(MI->getRawDest())) {
+ Builder.CreateAssumption(Builder.CreateIsNull(MI->getLength()));
+ return eraseInstFromFunction(CI);
+ }
+
if (Changed) return II;
}
diff --git a/llvm/test/Transforms/InstCombine/mem-intrinsics.ll b/llvm/test/Transforms/InstCombine/mem-intrinsics.ll
new file mode 100644
index 0000000000000..5448d3c20fb12
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/mem-intrinsics.ll
@@ -0,0 +1,77 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+define void @memset_null(i64 %len) {
+; CHECK-LABEL: define void @memset_null(
+; CHECK-SAME: i64 [[LEN:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]])
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memset.p0.i64(ptr null, i8 0, i64 %len, i1 false)
+ ret void
+}
+
+define void @memset_null_ub() {
+; CHECK-LABEL: define void @memset_null_ub() {
+; CHECK-NEXT: store i64 poison, ptr null, align 4294967296
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memset.p0.i64(ptr null, i8 0, i64 8, i1 false)
+ ret void
+}
+
+define void @memcpy_null_src(ptr %dst, i64 %len) {
+; CHECK-LABEL: define void @memcpy_null_src(
+; CHECK-SAME: ptr [[DST:%.*]], i64 [[LEN:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]])
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memcpy.p0.i64(ptr %dst, ptr null, i64 %len, i1 false)
+ ret void
+}
+
+define void @memmove_null_src(ptr %dst, i64 %len) {
+; CHECK-LABEL: define void @memmove_null_src(
+; CHECK-SAME: ptr [[DST:%.*]], i64 [[LEN:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]])
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memmove.p0.i64(ptr %dst, ptr null, i64 %len, i1 false)
+ ret void
+}
+
+define void @memset_element_atomic(i64 %len) {
+; CHECK-LABEL: define void @memset_element_atomic(
+; CHECK-SAME: i64 [[LEN:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i64 [[LEN]], 0
+; CHECK-NEXT: call void @llvm.assume(i1 [[TMP1]])
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memset.element.unordered.atomic.p0.i64(ptr align 1 null, i8 0, i64 %len, i32 1)
+ ret void
+}
+
+; negative tests
+
+define void @memset_null_volatile(i64 %len) {
+; CHECK-LABEL: define void @memset_null_volatile(
+; CHECK-SAME: i64 [[LEN:%.*]]) {
+; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr null, i8 0, i64 [[LEN]], i1 true)
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memset.p0.i64(ptr null, i8 0, i64 %len, i1 true)
+ ret void
+}
+
+define void @memset_null_is_defined(i64 %len) null_pointer_is_valid {
+; CHECK-LABEL: define void @memset_null_is_defined(
+; CHECK-SAME: i64 [[LEN:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 4294967296 null, i8 0, i64 [[LEN]], i1 false)
+; CHECK-NEXT: ret void
+;
+ call void @llvm.memset.p0.i64(ptr null, i8 0, i64 %len, i1 false)
+ ret void
+}
diff --git a/llvm/test/Transforms/InstCombine/mempcpy.ll b/llvm/test/Transforms/InstCombine/mempcpy.ll
index c996758a919d9..82c34f8a864ce 100644
--- a/llvm/test/Transforms/InstCombine/mempcpy.ll
+++ b/llvm/test/Transforms/InstCombine/mempcpy.ll
@@ -55,7 +55,7 @@ define ptr @memcpy_big_const_n(ptr %d, ptr nocapture readonly %s) {
define i32 @PR48810() {
; CHECK-LABEL: @PR48810(
-; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 1 undef, ptr align 4294967296 null, i64 undef, i1 false)
+; CHECK-NEXT: store i1 true, ptr poison, align 1
; CHECK-NEXT: ret i32 undef
;
%r = call dereferenceable(1) ptr @mempcpy(ptr undef, ptr null, i64 undef)
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