[llvm] [Loads] Check if Ptr can be freed between Assume and CtxI. (PR #161255)
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Fri Oct 3 07:22:04 PDT 2025
https://github.com/fhahn updated https://github.com/llvm/llvm-project/pull/161255
>From b76915ba6ec4e800ab39b3b768ebffdd1dbf06f5 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Mon, 29 Sep 2025 19:21:10 +0100
Subject: [PATCH] [Loads] Check if Ptr can be freed between Assume and CtxI.
When using information from dereferenceable assumptions, we need to make
sure that the memory is not freed between the assume and the specified
context instruction. Instead of just checking canBeFreed, check if there
any calls that may free between the assume and the context instruction.
Note that this also adjusts the context instruction to be the terminator
in the loop predecessor, if there is one and it is a branch (to avoid
things like invoke).
---
llvm/lib/Analysis/Loads.cpp | 18 +++++----
...able-info-from-assumption-constant-size.ll | 28 +++-----------
.../single-early-exit-deref-assumptions.ll | 37 ++++++++++++-------
3 files changed, 40 insertions(+), 43 deletions(-)
diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
index 0c4e3a2e3b233..ef26f81fef1d1 100644
--- a/llvm/lib/Analysis/Loads.cpp
+++ b/llvm/lib/Analysis/Loads.cpp
@@ -37,17 +37,13 @@ static bool isDereferenceableAndAlignedPointerViaAssumption(
function_ref<bool(const RetainedKnowledge &RK)> CheckSize,
const DataLayout &DL, const Instruction *CtxI, AssumptionCache *AC,
const DominatorTree *DT) {
- // Dereferenceable information from assumptions is only valid if the value
- // cannot be freed between the assumption and use. For now just use the
- // information for values that cannot be freed in the function.
- // TODO: More precisely check if the pointer can be freed between assumption
- // and use.
- if (!CtxI || Ptr->canBeFreed())
+ if (!CtxI)
return false;
/// Look through assumes to see if both dereferencability and alignment can
/// be proven by an assume if needed.
RetainedKnowledge AlignRK;
RetainedKnowledge DerefRK;
+ bool PtrCanBeFreed = Ptr->canBeFreed();
bool IsAligned = Ptr->getPointerAlignment(DL) >= Alignment;
return getKnowledgeForValue(
Ptr, {Attribute::Dereferenceable, Attribute::Alignment}, *AC,
@@ -56,7 +52,11 @@ static bool isDereferenceableAndAlignedPointerViaAssumption(
return false;
if (RK.AttrKind == Attribute::Alignment)
AlignRK = std::max(AlignRK, RK);
- if (RK.AttrKind == Attribute::Dereferenceable)
+
+ // Dereferenceable information from assumptions is only valid if the
+ // value cannot be freed between the assumption and use.
+ if ((!PtrCanBeFreed || willNotFreeBetween(Assume, CtxI)) &&
+ RK.AttrKind == Attribute::Dereferenceable)
DerefRK = std::max(DerefRK, RK);
IsAligned |= AlignRK && AlignRK.ArgValue >= Alignment.value();
if (IsAligned && DerefRK && CheckSize(DerefRK))
@@ -391,6 +391,10 @@ bool llvm::isDereferenceableAndAlignedInLoop(
return false;
Instruction *HeaderFirstNonPHI = &*L->getHeader()->getFirstNonPHIIt();
+ if (BasicBlock *LoopPred = L->getLoopPredecessor()) {
+ if (isa<BranchInst>(LoopPred->getTerminator()))
+ HeaderFirstNonPHI = LoopPred->getTerminator();
+ }
return isDereferenceableAndAlignedPointerViaAssumption(
Base, Alignment,
[&SE, AccessSizeSCEV, &LoopGuards](const RetainedKnowledge &RK) {
diff --git a/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll b/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll
index 75420d40f2aad..bcea03a6b9ba8 100644
--- a/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll
+++ b/llvm/test/Transforms/LoopVectorize/dereferenceable-info-from-assumption-constant-size.ll
@@ -1182,31 +1182,13 @@ define void @deref_assumption_in_header_constant_trip_count_nofree_via_context(p
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
-; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[PRED_LOAD_CONTINUE2:.*]] ]
+; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i32, ptr [[A]], i64 [[INDEX]]
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr inbounds i32, ptr [[B]], i64 [[INDEX]]
; CHECK-NEXT: [[WIDE_LOAD1:%.*]] = load <2 x i32>, ptr [[TMP0]], align 4
-; CHECK-NEXT: [[TMP2:%.*]] = icmp slt <2 x i32> [[WIDE_LOAD1]], zeroinitializer
-; CHECK-NEXT: [[TMP13:%.*]] = extractelement <2 x i1> [[TMP2]], i32 0
-; CHECK-NEXT: br i1 [[TMP13]], label %[[PRED_LOAD_IF:.*]], label %[[PRED_LOAD_CONTINUE:.*]]
-; CHECK: [[PRED_LOAD_IF]]:
-; CHECK-NEXT: [[TMP3:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT: [[TMP4:%.*]] = getelementptr i32, ptr [[A]], i64 [[TMP3]]
-; CHECK-NEXT: [[TMP5:%.*]] = load i32, ptr [[TMP4]], align 4
-; CHECK-NEXT: [[TMP6:%.*]] = insertelement <2 x i32> poison, i32 [[TMP5]], i32 0
-; CHECK-NEXT: br label %[[PRED_LOAD_CONTINUE]]
-; CHECK: [[PRED_LOAD_CONTINUE]]:
-; CHECK-NEXT: [[TMP7:%.*]] = phi <2 x i32> [ poison, %[[VECTOR_BODY]] ], [ [[TMP6]], %[[PRED_LOAD_IF]] ]
-; CHECK-NEXT: [[TMP8:%.*]] = extractelement <2 x i1> [[TMP2]], i32 1
-; CHECK-NEXT: br i1 [[TMP8]], label %[[PRED_LOAD_IF1:.*]], label %[[PRED_LOAD_CONTINUE2]]
-; CHECK: [[PRED_LOAD_IF1]]:
-; CHECK-NEXT: [[TMP9:%.*]] = add i64 [[INDEX]], 1
-; CHECK-NEXT: [[TMP10:%.*]] = getelementptr i32, ptr [[A]], i64 [[TMP9]]
-; CHECK-NEXT: [[TMP11:%.*]] = load i32, ptr [[TMP10]], align 4
-; CHECK-NEXT: [[TMP12:%.*]] = insertelement <2 x i32> [[TMP7]], i32 [[TMP11]], i32 1
-; CHECK-NEXT: br label %[[PRED_LOAD_CONTINUE2]]
-; CHECK: [[PRED_LOAD_CONTINUE2]]:
-; CHECK-NEXT: [[WIDE_LOAD:%.*]] = phi <2 x i32> [ [[TMP7]], %[[PRED_LOAD_CONTINUE]] ], [ [[TMP12]], %[[PRED_LOAD_IF1]] ]
-; CHECK-NEXT: [[PREDPHI:%.*]] = select <2 x i1> [[TMP2]], <2 x i32> [[WIDE_LOAD]], <2 x i32> [[WIDE_LOAD1]]
+; CHECK-NEXT: [[TMP2:%.*]] = icmp sge <2 x i32> [[WIDE_LOAD1]], zeroinitializer
+; CHECK-NEXT: [[WIDE_LOAD2:%.*]] = load <2 x i32>, ptr [[TMP1]], align 4
+; CHECK-NEXT: [[PREDPHI:%.*]] = select <2 x i1> [[TMP2]], <2 x i32> [[WIDE_LOAD1]], <2 x i32> [[WIDE_LOAD2]]
; CHECK-NEXT: [[TMP14:%.*]] = getelementptr inbounds i32, ptr [[C]], i64 [[INDEX]]
; CHECK-NEXT: store <2 x i32> [[PREDPHI]], ptr [[TMP14]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
diff --git a/llvm/test/Transforms/LoopVectorize/single-early-exit-deref-assumptions.ll b/llvm/test/Transforms/LoopVectorize/single-early-exit-deref-assumptions.ll
index f7946206931c2..cc3bda4a7f43b 100644
--- a/llvm/test/Transforms/LoopVectorize/single-early-exit-deref-assumptions.ll
+++ b/llvm/test/Transforms/LoopVectorize/single-early-exit-deref-assumptions.ll
@@ -504,24 +504,35 @@ exit:
define i64 @early_exit_alignment_and_deref_known_via_assumption_with_constant_size_nofree_via_context(ptr noalias %p1, ptr noalias %p2) nosync {
; CHECK-LABEL: define i64 @early_exit_alignment_and_deref_known_via_assumption_with_constant_size_nofree_via_context(
; CHECK-SAME: ptr noalias [[P1:%.*]], ptr noalias [[P2:%.*]]) #[[ATTR1:[0-9]+]] {
-; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[P1]], i64 4), "dereferenceable"(ptr [[P1]], i64 1024) ]
; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[P2]], i64 4), "dereferenceable"(ptr [[P2]], i64 1024) ]
-; CHECK-NEXT: br label %[[LOOP:.*]]
-; CHECK: [[LOOP]]:
-; CHECK-NEXT: [[INDEX1:%.*]] = phi i64 [ [[INDEX_NEXT:%.*]], %[[LOOP_INC:.*]] ], [ 0, %[[ENTRY]] ]
+; CHECK-NEXT: br label %[[VECTOR_PH:.*]]
+; CHECK: [[VECTOR_PH]]:
+; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
+; CHECK: [[VECTOR_BODY]]:
+; CHECK-NEXT: [[INDEX1:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT3:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[ARRAYIDX2:%.*]] = getelementptr inbounds i8, ptr [[P1]], i64 [[INDEX1]]
-; CHECK-NEXT: [[LD1:%.*]] = load i8, ptr [[ARRAYIDX2]], align 1
+; CHECK-NEXT: [[WIDE_LOAD:%.*]] = load <4 x i8>, ptr [[ARRAYIDX2]], align 1
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[P2]], i64 [[INDEX1]]
-; CHECK-NEXT: [[LD2:%.*]] = load i8, ptr [[TMP1]], align 1
-; CHECK-NEXT: [[CMP3:%.*]] = icmp eq i8 [[LD1]], [[LD2]]
-; CHECK-NEXT: br i1 [[CMP3]], label %[[LOOP_INC]], label %[[LOOP_END:.*]]
-; CHECK: [[LOOP_INC]]:
-; CHECK-NEXT: [[INDEX_NEXT]] = add i64 [[INDEX1]], 1
-; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[INDEX_NEXT]], 1024
-; CHECK-NEXT: br i1 [[EXITCOND]], label %[[LOOP]], label %[[LOOP_END]]
+; CHECK-NEXT: [[WIDE_LOAD2:%.*]] = load <4 x i8>, ptr [[TMP1]], align 1
+; CHECK-NEXT: [[TMP2:%.*]] = icmp ne <4 x i8> [[WIDE_LOAD]], [[WIDE_LOAD2]]
+; CHECK-NEXT: [[INDEX_NEXT3]] = add nuw i64 [[INDEX1]], 4
+; CHECK-NEXT: [[TMP3:%.*]] = freeze <4 x i1> [[TMP2]]
+; CHECK-NEXT: [[TMP4:%.*]] = call i1 @llvm.vector.reduce.or.v4i1(<4 x i1> [[TMP3]])
+; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i64 [[INDEX_NEXT3]], 1024
+; CHECK-NEXT: [[TMP6:%.*]] = or i1 [[TMP4]], [[TMP5]]
+; CHECK-NEXT: br i1 [[TMP6]], label %[[MIDDLE_SPLIT:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
+; CHECK: [[MIDDLE_SPLIT]]:
+; CHECK-NEXT: br i1 [[TMP4]], label %[[VECTOR_EARLY_EXIT:.*]], label %[[MIDDLE_BLOCK:.*]]
+; CHECK: [[MIDDLE_BLOCK]]:
+; CHECK-NEXT: br label %[[LOOP_END:.*]]
+; CHECK: [[VECTOR_EARLY_EXIT]]:
+; CHECK-NEXT: [[TMP7:%.*]] = call i64 @llvm.experimental.cttz.elts.i64.v4i1(<4 x i1> [[TMP2]], i1 true)
+; CHECK-NEXT: [[TMP8:%.*]] = add i64 [[INDEX1]], [[TMP7]]
+; CHECK-NEXT: br label %[[LOOP_END]]
; CHECK: [[LOOP_END]]:
-; CHECK-NEXT: [[RETVAL:%.*]] = phi i64 [ [[INDEX1]], %[[LOOP]] ], [ -1, %[[LOOP_INC]] ]
+; CHECK-NEXT: [[RETVAL:%.*]] = phi i64 [ -1, %[[MIDDLE_BLOCK]] ], [ [[TMP8]], %[[VECTOR_EARLY_EXIT]] ]
; CHECK-NEXT: ret i64 [[RETVAL]]
;
entry:
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