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[Analysis] Bail out for negative offsets in isDereferenceableAndAlign…
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…edInLoop (llvm#99490)

This patch now bails out explicitly for negative offsets so that it's
more consistent with the unsigned remainder and add calculations,
and it fixes a genuine bug as shown with the new test.
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@david-arm
david-arm authored Jul 22, 2024
1 parent f406d83 commit 102d168
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Showing 2 changed files with 120 additions and 15 deletions.
7 changes: 7 additions & 0 deletions llvm/lib/Analysis/Loads.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -313,6 +313,13 @@ bool llvm::isDereferenceableAndAlignedInLoop(LoadInst *LI, Loop *L,
const auto *Offset = dyn_cast<SCEVConstant>(StartS->getOperand(0));
const auto *NewBase = dyn_cast<SCEVUnknown>(StartS->getOperand(1));
if (StartS->getNumOperands() == 2 && Offset && NewBase) {
// The following code below assumes the offset is unsigned, but GEP
// offsets are treated as signed so we can end up with a signed value
// here too. For example, suppose the initial PHI value is (i8 255),
// the offset will be treated as (i8 -1) and sign-extended to (i64 -1).
if (Offset->getAPInt().isNegative())
return false;

// For the moment, restrict ourselves to the case where the offset is a
// multiple of the requested alignment and the base is aligned.
// TODO: generalize if a case found which warrants
Expand Down
128 changes: 113 additions & 15 deletions llvm/test/Transforms/LoopVectorize/load-deref-pred-align.ll
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes=loop-vectorize -force-vector-width=2 -force-vector-interleave=1 -S %s | FileCheck %s

target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128-ni:1"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128-ni:1-p:16:16:16:16"

declare void @init(ptr nocapture nofree)

Expand All @@ -17,7 +17,7 @@ define i16 @test_access_size_not_multiple_of_align(i64 %len, ptr %test_base) {
; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[PRED_LOAD_CONTINUE2:%.*]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i16> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP16:%.*]], [[PRED_LOAD_CONTINUE2]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i16> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP15:%.*]], [[PRED_LOAD_CONTINUE2]] ]
; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[INDEX]], 0
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[TEST_BASE:%.*]], i64 [[TMP0]]
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds i8, ptr [[TMP1]], i32 0
Expand All @@ -43,16 +43,16 @@ define i16 @test_access_size_not_multiple_of_align(i64 %len, ptr %test_base) {
; CHECK: pred.load.continue2:
; CHECK-NEXT: [[TMP14:%.*]] = phi <2 x i16> [ [[TMP8]], [[PRED_LOAD_CONTINUE]] ], [ [[TMP13]], [[PRED_LOAD_IF1]] ]
; CHECK-NEXT: [[PREDPHI:%.*]] = select <2 x i1> [[TMP3]], <2 x i16> [[TMP14]], <2 x i16> zeroinitializer
; CHECK-NEXT: [[TMP16]] = add <2 x i16> [[VEC_PHI]], [[PREDPHI]]
; CHECK-NEXT: [[TMP15]] = add <2 x i16> [[VEC_PHI]], [[PREDPHI]]
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
; CHECK-NEXT: [[TMP17:%.*]] = icmp eq i64 [[INDEX_NEXT]], 4096
; CHECK-NEXT: br i1 [[TMP17]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK-NEXT: [[TMP16:%.*]] = icmp eq i64 [[INDEX_NEXT]], 4096
; CHECK-NEXT: br i1 [[TMP16]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK: middle.block:
; CHECK-NEXT: [[TMP18:%.*]] = call i16 @llvm.vector.reduce.add.v2i16(<2 x i16> [[TMP16]])
; CHECK-NEXT: [[TMP17:%.*]] = call i16 @llvm.vector.reduce.add.v2i16(<2 x i16> [[TMP15]])
; CHECK-NEXT: br i1 true, label [[LOOP_EXIT:%.*]], label [[SCALAR_PH]]
; CHECK: scalar.ph:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i64 [ 4096, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i16 [ [[TMP18]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i16 [ [[TMP17]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
Expand All @@ -72,7 +72,7 @@ define i16 @test_access_size_not_multiple_of_align(i64 %len, ptr %test_base) {
; CHECK-NEXT: [[EXIT:%.*]] = icmp eq i64 [[IV]], 4095
; CHECK-NEXT: br i1 [[EXIT]], label [[LOOP_EXIT]], label [[LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK: loop_exit:
; CHECK-NEXT: [[ACCUM_NEXT_LCSSA:%.*]] = phi i16 [ [[ACCUM_NEXT]], [[LATCH]] ], [ [[TMP18]], [[MIDDLE_BLOCK]] ]
; CHECK-NEXT: [[ACCUM_NEXT_LCSSA:%.*]] = phi i16 [ [[ACCUM_NEXT]], [[LATCH]] ], [ [[TMP17]], [[MIDDLE_BLOCK]] ]
; CHECK-NEXT: ret i16 [[ACCUM_NEXT_LCSSA]]
;
entry:
Expand Down Expand Up @@ -114,7 +114,7 @@ define i32 @test_access_size_multiple_of_align_but_offset_by_1(i64 %len, ptr %te
; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[PRED_LOAD_CONTINUE2:%.*]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP16:%.*]], [[PRED_LOAD_CONTINUE2]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP15:%.*]], [[PRED_LOAD_CONTINUE2]] ]
; CHECK-NEXT: [[TMP0:%.*]] = add i64 [[INDEX]], 0
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[TEST_BASE:%.*]], i64 [[TMP0]]
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds i8, ptr [[TMP1]], i32 0
Expand All @@ -140,16 +140,16 @@ define i32 @test_access_size_multiple_of_align_but_offset_by_1(i64 %len, ptr %te
; CHECK: pred.load.continue2:
; CHECK-NEXT: [[TMP14:%.*]] = phi <2 x i32> [ [[TMP8]], [[PRED_LOAD_CONTINUE]] ], [ [[TMP13]], [[PRED_LOAD_IF1]] ]
; CHECK-NEXT: [[PREDPHI:%.*]] = select <2 x i1> [[TMP3]], <2 x i32> [[TMP14]], <2 x i32> zeroinitializer
; CHECK-NEXT: [[TMP16]] = add <2 x i32> [[VEC_PHI]], [[PREDPHI]]
; CHECK-NEXT: [[TMP15]] = add <2 x i32> [[VEC_PHI]], [[PREDPHI]]
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
; CHECK-NEXT: [[TMP17:%.*]] = icmp eq i64 [[INDEX_NEXT]], 4096
; CHECK-NEXT: br i1 [[TMP17]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK-NEXT: [[TMP16:%.*]] = icmp eq i64 [[INDEX_NEXT]], 4096
; CHECK-NEXT: br i1 [[TMP16]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK: middle.block:
; CHECK-NEXT: [[TMP18:%.*]] = call i32 @llvm.vector.reduce.add.v2i32(<2 x i32> [[TMP16]])
; CHECK-NEXT: [[TMP17:%.*]] = call i32 @llvm.vector.reduce.add.v2i32(<2 x i32> [[TMP15]])
; CHECK-NEXT: br i1 true, label [[LOOP_EXIT:%.*]], label [[SCALAR_PH]]
; CHECK: scalar.ph:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i64 [ 4096, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP18]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP17]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
Expand All @@ -169,7 +169,7 @@ define i32 @test_access_size_multiple_of_align_but_offset_by_1(i64 %len, ptr %te
; CHECK-NEXT: [[EXIT:%.*]] = icmp eq i64 [[IV]], 4095
; CHECK-NEXT: br i1 [[EXIT]], label [[LOOP_EXIT]], label [[LOOP]], !llvm.loop [[LOOP5:![0-9]+]]
; CHECK: loop_exit:
; CHECK-NEXT: [[ACCUM_NEXT_LCSSA:%.*]] = phi i32 [ [[ACCUM_NEXT]], [[LATCH]] ], [ [[TMP18]], [[MIDDLE_BLOCK]] ]
; CHECK-NEXT: [[ACCUM_NEXT_LCSSA:%.*]] = phi i32 [ [[ACCUM_NEXT]], [[LATCH]] ], [ [[TMP17]], [[MIDDLE_BLOCK]] ]
; CHECK-NEXT: ret i32 [[ACCUM_NEXT_LCSSA]]
;
entry:
Expand Down Expand Up @@ -198,3 +198,101 @@ latch:
loop_exit:
ret i32 %accum.next
}


; Test where offset relative to alloca is negative and we shouldn't
; treat predicated loads as being always dereferenceable.
define i8 @test_negative_off(i16 %len, ptr %test_base) {
; CHECK-LABEL: @test_negative_off(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[ALLOCA:%.*]] = alloca [64638 x i8], align 1
; CHECK-NEXT: call void @init(ptr [[ALLOCA]])
; CHECK-NEXT: br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
; CHECK: vector.ph:
; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[PRED_LOAD_CONTINUE2:%.*]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i8> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP18:%.*]], [[PRED_LOAD_CONTINUE2]] ]
; CHECK-NEXT: [[DOTCAST:%.*]] = trunc i32 [[INDEX]] to i16
; CHECK-NEXT: [[OFFSET_IDX:%.*]] = add i16 -1000, [[DOTCAST]]
; CHECK-NEXT: [[TMP0:%.*]] = add i16 [[OFFSET_IDX]], 0
; CHECK-NEXT: [[TMP1:%.*]] = add i16 [[OFFSET_IDX]], 1
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds i1, ptr [[TEST_BASE:%.*]], i16 [[TMP0]]
; CHECK-NEXT: [[TMP3:%.*]] = getelementptr inbounds i1, ptr [[TEST_BASE]], i16 [[TMP1]]
; CHECK-NEXT: [[TMP4:%.*]] = load i1, ptr [[TMP2]], align 1
; CHECK-NEXT: [[TMP5:%.*]] = load i1, ptr [[TMP3]], align 1
; CHECK-NEXT: [[TMP6:%.*]] = insertelement <2 x i1> poison, i1 [[TMP4]], i32 0
; CHECK-NEXT: [[TMP7:%.*]] = insertelement <2 x i1> [[TMP6]], i1 [[TMP5]], i32 1
; CHECK-NEXT: [[TMP8:%.*]] = extractelement <2 x i1> [[TMP7]], i32 0
; CHECK-NEXT: br i1 [[TMP8]], label [[PRED_LOAD_IF:%.*]], label [[PRED_LOAD_CONTINUE:%.*]]
; CHECK: pred.load.if:
; CHECK-NEXT: [[TMP9:%.*]] = getelementptr i8, ptr [[ALLOCA]], i16 [[TMP0]]
; CHECK-NEXT: [[TMP10:%.*]] = load i8, ptr [[TMP9]], align 1
; CHECK-NEXT: [[TMP11:%.*]] = insertelement <2 x i8> poison, i8 [[TMP10]], i32 0
; CHECK-NEXT: br label [[PRED_LOAD_CONTINUE]]
; CHECK: pred.load.continue:
; CHECK-NEXT: [[TMP12:%.*]] = phi <2 x i8> [ poison, [[VECTOR_BODY]] ], [ [[TMP11]], [[PRED_LOAD_IF]] ]
; CHECK-NEXT: [[TMP13:%.*]] = extractelement <2 x i1> [[TMP7]], i32 1
; CHECK-NEXT: br i1 [[TMP13]], label [[PRED_LOAD_IF1:%.*]], label [[PRED_LOAD_CONTINUE2]]
; CHECK: pred.load.if1:
; CHECK-NEXT: [[TMP14:%.*]] = getelementptr i8, ptr [[ALLOCA]], i16 [[TMP1]]
; CHECK-NEXT: [[TMP15:%.*]] = load i8, ptr [[TMP14]], align 1
; CHECK-NEXT: [[TMP16:%.*]] = insertelement <2 x i8> [[TMP12]], i8 [[TMP15]], i32 1
; CHECK-NEXT: br label [[PRED_LOAD_CONTINUE2]]
; CHECK: pred.load.continue2:
; CHECK-NEXT: [[TMP17:%.*]] = phi <2 x i8> [ [[TMP12]], [[PRED_LOAD_CONTINUE]] ], [ [[TMP16]], [[PRED_LOAD_IF1]] ]
; CHECK-NEXT: [[PREDPHI:%.*]] = select <2 x i1> [[TMP7]], <2 x i8> [[TMP17]], <2 x i8> zeroinitializer
; CHECK-NEXT: [[TMP18]] = add <2 x i8> [[VEC_PHI]], [[PREDPHI]]
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 2
; CHECK-NEXT: [[TMP19:%.*]] = icmp eq i32 [[INDEX_NEXT]], 12
; CHECK-NEXT: br i1 [[TMP19]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK: middle.block:
; CHECK-NEXT: [[TMP20:%.*]] = call i8 @llvm.vector.reduce.add.v2i8(<2 x i8> [[TMP18]])
; CHECK-NEXT: br i1 true, label [[LOOP_EXIT:%.*]], label [[SCALAR_PH]]
; CHECK: scalar.ph:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i16 [ -988, [[MIDDLE_BLOCK]] ], [ -1000, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i8 [ [[TMP20]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i16 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LATCH:%.*]] ]
; CHECK-NEXT: [[ACCUM:%.*]] = phi i8 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[ACCUM_NEXT:%.*]], [[LATCH]] ]
; CHECK-NEXT: [[IV_NEXT]] = add i16 [[IV]], 1
; CHECK-NEXT: [[TEST_ADDR:%.*]] = getelementptr inbounds i1, ptr [[TEST_BASE]], i16 [[IV]]
; CHECK-NEXT: [[EARLYCND:%.*]] = load i1, ptr [[TEST_ADDR]], align 1
; CHECK-NEXT: br i1 [[EARLYCND]], label [[PRED:%.*]], label [[LATCH]]
; CHECK: pred:
; CHECK-NEXT: [[ADDR:%.*]] = getelementptr i8, ptr [[ALLOCA]], i16 [[IV]]
; CHECK-NEXT: [[VAL:%.*]] = load i8, ptr [[ADDR]], align 1
; CHECK-NEXT: br label [[LATCH]]
; CHECK: latch:
; CHECK-NEXT: [[VAL_PHI:%.*]] = phi i8 [ 0, [[LOOP]] ], [ [[VAL]], [[PRED]] ]
; CHECK-NEXT: [[ACCUM_NEXT]] = add i8 [[ACCUM]], [[VAL_PHI]]
; CHECK-NEXT: [[EXIT:%.*]] = icmp ugt i16 [[IV]], -990
; CHECK-NEXT: br i1 [[EXIT]], label [[LOOP_EXIT]], label [[LOOP]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK: loop_exit:
; CHECK-NEXT: [[ACCUM_NEXT_LCSSA:%.*]] = phi i8 [ [[ACCUM_NEXT]], [[LATCH]] ], [ [[TMP20]], [[MIDDLE_BLOCK]] ]
; CHECK-NEXT: ret i8 [[ACCUM_NEXT_LCSSA]]
;
entry:
%alloca = alloca [64638 x i8]
call void @init(ptr %alloca)
br label %loop
loop:
%iv = phi i16 [ -1000, %entry ], [ %iv.next, %latch ]
%accum = phi i8 [ 0, %entry ], [ %accum.next, %latch ]
%iv.next = add i16 %iv, 1
%test_addr = getelementptr inbounds i1, ptr %test_base, i16 %iv
%earlycnd = load i1, ptr %test_addr
br i1 %earlycnd, label %pred, label %latch
pred:
%addr = getelementptr i8, ptr %alloca, i16 %iv
%val = load i8, ptr %addr
br label %latch
latch:
%val.phi = phi i8 [ 0, %loop ], [ %val, %pred ]
%accum.next = add i8 %accum, %val.phi
%exit = icmp ugt i16 %iv, -990
br i1 %exit, label %loop_exit, label %loop
loop_exit:
ret i8 %accum.next
}

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