From 89d480ff228395ad0b67cb2373c56a81ea44e78e Mon Sep 17 00:00:00 2001 From: Florian Hahn Date: Thu, 13 Feb 2025 20:41:23 +0100 Subject: [PATCH] [AssumeBundles] Dereferenceable used in bundle only applies at assume. (#126117) Update LangRef and code using `Dereferenceable` in assume bundles to only use the information if it is safe at the point of use. `Dereferenceable` in an assume bundle is only guaranteed at the point of the assumption, but may not be guaranteed at later points, because the pointer may have been freed. Update code using `Dereferenceable` to only use it if the pointer cannot be freed. This can further be refined to check if the pointer could be freed between assume and use. This follows up on https://github.com/llvm/llvm-project/pull/123196. With that change, it should be safe to expose dereferenceable assumptions more widely as in https://github.com/llvm/llvm-project/pull/121789 PR: https://github.com/llvm/llvm-project/pull/126117 --- llvm/docs/LangRef.rst | 9 +- llvm/lib/Analysis/Loads.cpp | 9 +- .../ValueTracking/assume-queries-counter.ll | 2 +- llvm/test/Analysis/ValueTracking/assume.ll | 4 +- .../LICM/hoist-speculatable-load.ll | 110 +++++++++++++++++- ...able-info-from-assumption-constant-size.ll | 4 +- .../SimplifyCFG/speculate-derefable-load.ll | 68 ++++++++++- 7 files changed, 191 insertions(+), 15 deletions(-) diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index b9f681f2feed8..8ea5d35cb63e9 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -1474,7 +1474,9 @@ Currently, only the following parameter attributes are defined: ``null_pointer_is_valid`` function attribute is present. ``n`` should be a positive number. The pointer should be well defined, otherwise it is undefined behavior. This means ``dereferenceable()`` - implies ``noundef``. + implies ``noundef``. When used in an assume operand bundle, more restricted + semantics apply. See :ref:`assume operand bundles ` for + more details. ``dereferenceable_or_null()`` This indicates that the parameter or return value isn't both @@ -2929,6 +2931,11 @@ the behavior is undefined, unless one of the following exceptions applies: (including a zero alignment). If this is the case, then the pointer value must be a null pointer, otherwise the behavior is undefined. +* ``dereferenceable()`` operand bundles only guarantee the pointer is + dereferenceable at the point of the assumption. The pointer may not be + dereferenceable at later pointers, e.g. because it could have been + freed. + In addition to allowing operand bundles encoding function and parameter attributes, an assume operand bundle my also encode a ``separate_storage`` operand bundle. This has the form: diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp index 733a7988e5a73..b461c41d29e84 100644 --- a/llvm/lib/Analysis/Loads.cpp +++ b/llvm/lib/Analysis/Loads.cpp @@ -26,8 +26,6 @@ using namespace llvm; -extern cl::opt UseDerefAtPointSemantics; - static bool isAligned(const Value *Base, Align Alignment, const DataLayout &DL) { return Base->getPointerAlignment(DL) >= Alignment; @@ -171,7 +169,12 @@ static bool isDereferenceableAndAlignedPointer( Size, DL, CtxI, AC, DT, TLI, Visited, MaxDepth); - if (CtxI && (!UseDerefAtPointSemantics || !V->canBeFreed())) { + // 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 && !V->canBeFreed()) { /// Look through assumes to see if both dereferencability and alignment can /// be proven by an assume if needed. RetainedKnowledge AlignRK; diff --git a/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll b/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll index a53b90b7b448a..0223ab8c4b677 100644 --- a/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll +++ b/llvm/test/Analysis/ValueTracking/assume-queries-counter.ll @@ -47,7 +47,7 @@ define dso_local i1 @test2(ptr readonly %0) { ret i1 %2 } -define dso_local i32 @test4(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4(ptr readonly %0, i1 %cond) nofree nosync { ; COUNTER1-LABEL: @test4( ; COUNTER1-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4) ] ; COUNTER1-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] diff --git a/llvm/test/Analysis/ValueTracking/assume.ll b/llvm/test/Analysis/ValueTracking/assume.ll index 4c4b46c419968..298facfa3aa9d 100644 --- a/llvm/test/Analysis/ValueTracking/assume.ll +++ b/llvm/test/Analysis/ValueTracking/assume.ll @@ -57,7 +57,7 @@ define dso_local i1 @test2(ptr readonly %0) { ret i1 %2 } -define dso_local i32 @test4(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4(ptr readonly %0, i1 %cond) nofree nosync { ; CHECK-LABEL: @test4( ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4) ] ; CHECK-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] @@ -91,7 +91,7 @@ A: ret i32 %6 } -define dso_local i32 @test4a(ptr readonly %0, i1 %cond) { +define dso_local i32 @test4a(ptr readonly %0, i1 %cond) nofree nosync { ; CHECK-LABEL: @test4a( ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[TMP0:%.*]], i32 4), "align"(ptr [[TMP0]], i32 8) ] ; CHECK-NEXT: br i1 [[COND:%.*]], label [[A:%.*]], label [[B:%.*]] diff --git a/llvm/test/Transforms/LICM/hoist-speculatable-load.ll b/llvm/test/Transforms/LICM/hoist-speculatable-load.ll index 752cf3e99cbf5..85411428a402f 100644 --- a/llvm/test/Transforms/LICM/hoist-speculatable-load.ll +++ b/llvm/test/Transforms/LICM/hoist-speculatable-load.ll @@ -11,12 +11,12 @@ define void @f(i32 %ptr_i, ptr %ptr2, i1 %cond) { ; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 ; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] ; CHECK: for.body.lr.ph: -; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4 ; CHECK-NEXT: br label [[FOR_BODY:%.*]] ; CHECK: for.body: ; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] ; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] ; CHECK: if: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4, !invariant.load [[META0:![0-9]+]] ; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 ; CHECK-NEXT: br label [[IF_END]] ; CHECK: if.end: @@ -56,4 +56,112 @@ exit: ; preds = %if.end, %entry ret void } +define void @f_nofree_nosync(i32 %ptr_i, ptr %ptr2, i1 %cond) nofree nosync { +; CHECK-LABEL: @f_nofree_nosync( +; CHECK-NEXT: entry: +; CHECK-NEXT: [[PTR:%.*]] = inttoptr i32 [[PTR_I:%.*]] to ptr +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[PTR]], i32 16), "dereferenceable"(ptr [[PTR]], i32 16) ] +; CHECK-NEXT: br i1 [[COND:%.*]], label [[FOR_BODY_LR_PH:%.*]], label [[IF0:%.*]] +; CHECK: if0: +; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 +; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] +; CHECK: for.body.lr.ph: +; CHECK-NEXT: br label [[FOR_BODY:%.*]] +; CHECK: for.body: +; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] +; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] +; CHECK: if: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4, !invariant.load [[META0]] +; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 +; CHECK-NEXT: br label [[IF_END]] +; CHECK: if.end: +; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[I_08]], 1 +; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[INC]], 2 +; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[EXIT:%.*]] +; CHECK: exit: +; CHECK-NEXT: ret void +; +entry: + %ptr = inttoptr i32 %ptr_i to ptr + call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i32 16), "dereferenceable"(ptr %ptr, i32 16) ] + br i1 %cond, label %for.body.lr.ph, label %if0 + +if0: + store i32 0, ptr %ptr2, align 4 + br label %for.body.lr.ph + +for.body.lr.ph: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.lr.ph, %if.end + %i.08 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %if.end ] + br i1 %cond, label %if.end, label %if + +if: + %0 = load i32, ptr %ptr, align 4, !invariant.load !{} + store i32 %0, ptr %ptr2, align 4 + br label %if.end + +if.end: ; preds = %for.body + %inc = add nuw nsw i32 %i.08, 1 + %cmp = icmp slt i32 %inc, 2 + br i1 %cmp, label %for.body, label %exit + +exit: ; preds = %if.end, %entry + ret void +} + +define void @f_without_ptrtoint_and_with_nofree_nosync(ptr %ptr, ptr %ptr2, i1 %cond) nofree nosync { +; CHECK-LABEL: @f_without_ptrtoint_and_with_nofree_nosync( +; CHECK-NEXT: entry: +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[PTR:%.*]], i32 16), "dereferenceable"(ptr [[PTR]], i32 16) ] +; CHECK-NEXT: br i1 [[COND:%.*]], label [[FOR_BODY_LR_PH:%.*]], label [[IF0:%.*]] +; CHECK: if0: +; CHECK-NEXT: store i32 0, ptr [[PTR2:%.*]], align 4 +; CHECK-NEXT: br label [[FOR_BODY_LR_PH]] +; CHECK: for.body.lr.ph: +; CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr [[PTR]], align 4 +; CHECK-NEXT: br label [[FOR_BODY:%.*]] +; CHECK: for.body: +; CHECK-NEXT: [[I_08:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[INC:%.*]], [[IF_END:%.*]] ] +; CHECK-NEXT: br i1 [[COND]], label [[IF_END]], label [[IF:%.*]] +; CHECK: if: +; CHECK-NEXT: store i32 [[TMP0]], ptr [[PTR2]], align 4 +; CHECK-NEXT: br label [[IF_END]] +; CHECK: if.end: +; CHECK-NEXT: [[INC]] = add nuw nsw i32 [[I_08]], 1 +; CHECK-NEXT: [[CMP:%.*]] = icmp slt i32 [[INC]], 2 +; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[EXIT:%.*]] +; CHECK: exit: +; CHECK-NEXT: ret void +; +entry: + call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i32 16), "dereferenceable"(ptr %ptr, i32 16) ] + br i1 %cond, label %for.body.lr.ph, label %if0 + +if0: + store i32 0, ptr %ptr2, align 4 + br label %for.body.lr.ph + +for.body.lr.ph: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.lr.ph, %if.end + %i.08 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %if.end ] + br i1 %cond, label %if.end, label %if + +if: + %0 = load i32, ptr %ptr, align 4, !invariant.load !{} + store i32 %0, ptr %ptr2, align 4 + br label %if.end + +if.end: ; preds = %for.body + %inc = add nuw nsw i32 %i.08, 1 + %cmp = icmp slt i32 %inc, 2 + br i1 %cmp, label %for.body, label %exit + +exit: ; preds = %if.end, %entry + ret void +} + declare void @llvm.assume(i1 noundef) 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 90671689f1dce..13780a684f9ce 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 @@ -1,5 +1,5 @@ ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 -; RUN: opt -p loop-vectorize -force-vector-width=2 -use-dereferenceable-at-point-semantics -S %s | FileCheck %s +; RUN: opt -p loop-vectorize -force-vector-width=2 -S %s | FileCheck %s declare void @llvm.assume(i1) @@ -1411,7 +1411,6 @@ exit: } ; %a may be freed between the dereferenceable assumption and accesses. -; It is not safe to use with -use-dereferenceable-at-point-semantics. define void @may_free_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr(ptr noalias %a, ptr noalias %b, ptr noalias %c) { ; CHECK-LABEL: define void @may_free_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr( ; CHECK-SAME: ptr noalias [[A:%.*]], ptr noalias [[B:%.*]], ptr noalias [[C:%.*]]) { @@ -1505,7 +1504,6 @@ exit: } ; %a may be freed between the dereferenceable assumption and accesses. -; It is not safe to use with -use-dereferenceable-at-point-semantics. define void @may_free_local_ptr_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr(ptr noalias %b, ptr noalias %c) nofree nosync { ; CHECK-LABEL: define void @may_free_local_ptr_align_deref_assumption_in_header_constant_trip_count_loop_invariant_ptr( ; CHECK-SAME: ptr noalias [[B:%.*]], ptr noalias [[C:%.*]]) #[[ATTR1]] { diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll b/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll index 0138433312ed8..b8c999d700aa7 100644 --- a/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll +++ b/llvm/test/Transforms/SimplifyCFG/speculate-derefable-load.ll @@ -4,10 +4,14 @@ define i64 @align_deref_align(i1 %c, ptr %p) { ; CHECK-LABEL: define i64 @align_deref_align( ; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) { -; CHECK-NEXT: [[ENTRY:.*:]] +; CHECK-NEXT: [[ENTRY:.*]]: ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]] +; CHECK: [[IF]]: ; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 -; CHECK-NEXT: [[RES:%.*]] = select i1 [[C]], i64 [[V]], i64 0 +; CHECK-NEXT: br label %[[EXIT]] +; CHECK: [[EXIT]]: +; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF]] ], [ 0, %[[ENTRY]] ] ; CHECK-NEXT: ret i64 [[RES]] ; entry: @@ -23,9 +27,64 @@ exit: ret i64 %res } +define i64 @align_deref_align_nofree_nosync(i1 %c, ptr %p) nofree nosync { +; CHECK-LABEL: define i64 @align_deref_align_nofree_nosync( +; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) #[[ATTR0:[0-9]+]] { +; CHECK-NEXT: [[ENTRY:.*:]] +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 +; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[C]], i64 [[V]], i64 0 +; CHECK-NEXT: ret i64 [[SPEC_SELECT]] +; +entry: + call void @llvm.assume(i1 true) [ "dereferenceable"(ptr %p, i64 8), "align"(ptr %p, i64 8) ] + br i1 %c, label %if, label %exit + +if: + %v = load i64, ptr %p, align 8 + br label %exit + +exit: + %res = phi i64 [ %v, %if ], [ 0, %entry ] + ret i64 %res +} + define i64 @assume_deref_align2(i1 %c1, i32 %x, ptr %p) { ; CHECK-LABEL: define i64 @assume_deref_align2( ; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) { +; CHECK-NEXT: [[ENTRY:.*]]: +; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] +; CHECK-NEXT: br i1 [[C1]], label %[[IF1:.*]], label %[[EXIT:.*]] +; CHECK: [[IF1]]: +; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10 +; CHECK-NEXT: br i1 [[C2]], label %[[IF2:.*]], label %[[EXIT]] +; CHECK: [[IF2]]: +; CHECK-NEXT: [[V:%.*]] = load i64, ptr [[P]], align 8 +; CHECK-NEXT: br label %[[EXIT]] +; CHECK: [[EXIT]]: +; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[V]], %[[IF2]] ], [ 1, %[[IF1]] ], [ 0, %[[ENTRY]] ] +; CHECK-NEXT: ret i64 [[RES]] +; +entry: + call void @llvm.assume(i1 true) [ "dereferenceable"(ptr %p, i64 8), "align"(ptr %p, i64 8) ] + br i1 %c1, label %if1, label %exit + +if1: + %c2 = icmp ugt i32 %x, 10 + br i1 %c2, label %if2, label %exit + +if2: + %v = load i64, ptr %p, align 8 + br label %exit + +exit: + %res = phi i64 [ %v, %if2 ], [ 1, %if1 ], [ 0, %entry ] + ret i64 %res +} + +define i64 @assume_deref_align2_nofree_nosync(i1 %c1, i32 %x, ptr %p) nofree nosync { +; CHECK-LABEL: define i64 @assume_deref_align2_nofree_nosync( +; CHECK-SAME: i1 [[C1:%.*]], i32 [[X:%.*]], ptr [[P:%.*]]) #[[ATTR0]] { ; CHECK-NEXT: [[ENTRY:.*:]] ; CHECK-NEXT: call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 8), "align"(ptr [[P]], i64 8) ] ; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[X]], 10 @@ -51,9 +110,10 @@ exit: ret i64 %res } -define i64 @assume_deref_align_not_dominating(i1 %c, ptr %p) { + +define i64 @assume_deref_align_not_dominating(i1 %c, ptr %p) nofree nosync { ; CHECK-LABEL: define i64 @assume_deref_align_not_dominating( -; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) { +; CHECK-SAME: i1 [[C:%.*]], ptr [[P:%.*]]) #[[ATTR0]] { ; CHECK-NEXT: [[ENTRY:.*]]: ; CHECK-NEXT: br i1 [[C]], label %[[IF:.*]], label %[[EXIT:.*]] ; CHECK: [[IF]]: