[llvm] [DSE] Update dereferenceable attributes when adjusting memintrinsic ptr (PR #125073)
Björn Pettersson via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 30 07:41:45 PST 2025
https://github.com/bjope updated https://github.com/llvm/llvm-project/pull/125073
>From 6b014c5c66d79ef99e3a7b4ddd6f6be99c781627 Mon Sep 17 00:00:00 2001
From: Bjorn Pettersson <bjorn.a.pettersson at ericsson.com>
Date: Thu, 30 Jan 2025 16:32:04 +0100
Subject: [PATCH 1/2] [DSE] Update dereferenceable attributes when adjusting
memintrinsic ptr
Consider IR like this
call void @llvm.memset.p0.i64(ptr dereferenceable(28) %p, i8 0, i64 28, i1 false)
store i32 1, ptr %p
It has been optimized like this:
%p2 = getelementptr inbounds i8, ptr %p, i64 4
call void @llvm.memset.p0.i64(ptr dereferenceable(28) %p2, i8 0, i64 24, i1 false)
store i32 1, ptr %p
As the input IR doesn't guarantee that it is OK to deref 28 bytes
starting at the adjusted pointer %p2 the transformation has been
a bit flawed.
With this patch we make sure to also adjust the size of any
dereferenceable/dereferenceable_or_null attributes when doing the
transform in tryToShorten (when adjusting the start pointer). So now
we will get dereferenceable(24) in the example above.
---
llvm/include/llvm/IR/InstrTypes.h | 5 ++++
.../Scalar/DeadStoreElimination.cpp | 18 +++++++++++
.../OverwriteStoreBegin.ll | 30 +++++++++++++++++++
3 files changed, 53 insertions(+)
diff --git a/llvm/include/llvm/IR/InstrTypes.h b/llvm/include/llvm/IR/InstrTypes.h
index 47ddc7555594c5..f26aafbe3f0ef8 100644
--- a/llvm/include/llvm/IR/InstrTypes.h
+++ b/llvm/include/llvm/IR/InstrTypes.h
@@ -1559,6 +1559,11 @@ class CallBase : public Instruction {
Attrs = Attrs.addDereferenceableParamAttr(getContext(), i, Bytes);
}
+ /// adds the dereferenceable attribute to the list of attributes.
+ void addDereferenceableOrNullParamAttr(unsigned i, uint64_t Bytes) {
+ Attrs = Attrs.addDereferenceableOrNullParamAttr(getContext(), i, Bytes);
+ }
+
/// adds the dereferenceable attribute to the list of attributes.
void addDereferenceableRetAttr(uint64_t Bytes) {
Attrs = Attrs.addDereferenceableRetAttr(getContext(), Bytes);
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 13f3de07c3c44d..c16134e3f01598 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -563,6 +563,23 @@ static void shortenAssignment(Instruction *Inst, Value *OriginalDest,
for_each(LinkedDVRAssigns, InsertAssignForOverlap);
}
+// Helper to trim or drop any dereferencable/dereferencable_or_null attributes
+// for a given argument, based on the new access being restricted to derefence
+// bytes in the range [Offset, Offset+Size).
+static void trimDereferencableAttrs(AnyMemIntrinsic *Intrinsic, unsigned Arg,
+ uint64_t Offset, uint64_t Size) {
+ uint64_t End = Offset + Size;
+ if (Intrinsic->getParamDereferenceableBytes(Arg) >= End)
+ Intrinsic->addDereferenceableParamAttr(Arg, Size);
+ else
+ Intrinsic->removeParamAttr(Arg, Attribute::Dereferenceable);
+ if (Intrinsic->getParamDereferenceableOrNullBytes(Arg) >= End)
+ Intrinsic->addDereferenceableOrNullParamAttr(Arg, Size);
+ else
+ Intrinsic->removeParamAttr(Arg, Attribute::DereferenceableOrNull);
+}
+
+
static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
uint64_t &DeadSize, int64_t KillingStart,
uint64_t KillingSize, bool IsOverwriteEnd) {
@@ -644,6 +661,7 @@ static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
DeadI->getIterator());
NewDestGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
DeadIntrinsic->setDest(NewDestGEP);
+ trimDereferencableAttrs(DeadIntrinsic, 0, ToRemoveSize, NewSize);
}
// Update attached dbg.assign intrinsics. Assume 8-bit byte.
diff --git a/llvm/test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll b/llvm/test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll
index bc1756f6ca9d1b..6c42d8e2c98338 100644
--- a/llvm/test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll
@@ -402,3 +402,33 @@ entry:
store i64 1, ptr %p, align 1
ret void
}
+
+; Verify that we adjust the dereferenceable attribute.
+define void @dereferenceable(ptr nocapture %p) {
+; CHECK-LABEL: @dereferenceable(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 4
+; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 4 dereferenceable(24) [[TMP0]], i8 0, i64 24, i1 false)
+; CHECK-NEXT: store i32 1, ptr [[P]], align 4
+; CHECK-NEXT: ret void
+;
+entry:
+ call void @llvm.memset.p0.i64(ptr dereferenceable(28) align 4 %p, i8 0, i64 28, i1 false)
+ store i32 1, ptr %p, align 4
+ ret void
+}
+
+; Verify that we adjust the dereferenceable_or_null attribute.
+define void @dereferenceable_or_null(ptr nocapture %p) {
+; CHECK-LABEL: @dereferenceable_or_null(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 8
+; CHECK-NEXT: call void @llvm.memset.p0.i64(ptr align 4 dereferenceable_or_null(20) [[TMP0]], i8 0, i64 20, i1 false)
+; CHECK-NEXT: store i64 1, ptr [[P]], align 4
+; CHECK-NEXT: ret void
+;
+entry:
+ call void @llvm.memset.p0.i64(ptr dereferenceable_or_null(28) align 4 %p, i8 0, i64 28, i1 false)
+ store i64 1, ptr %p, align 4
+ ret void
+}
>From f6f70258b0d5377324f884a6e03ea75d5d8a2db2 Mon Sep 17 00:00:00 2001
From: Bjorn Pettersson <bjorn.a.pettersson at ericsson.com>
Date: Thu, 30 Jan 2025 16:41:20 +0100
Subject: [PATCH 2/2] fixup formatting
---
llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp | 1 -
1 file changed, 1 deletion(-)
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index c16134e3f01598..50f964411aba80 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -579,7 +579,6 @@ static void trimDereferencableAttrs(AnyMemIntrinsic *Intrinsic, unsigned Arg,
Intrinsic->removeParamAttr(Arg, Attribute::DereferenceableOrNull);
}
-
static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
uint64_t &DeadSize, int64_t KillingStart,
uint64_t KillingSize, bool IsOverwriteEnd) {
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