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[InstCombine] Canonicalize gep T, (gep i8, base, C1), (Index + C2) …
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…into `gep T, (gep i8, base, C1 + C2 * sizeof(T)), Index` (#76177)

This patch tries to canonicalize `gep T, (gep i8, base, C1), (Index +
C2)` into `gep T, (gep i8, base, C1 + C2 * sizeof(T)), Index`.

Alive2: https://alive2.llvm.org/ce/z/dxShKF
Fixes regressions found in
#68882.
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@dtcxzyw
dtcxzyw committed Apr 25, 2024
1 parent f5953f4 commit 5a1d850
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40 changes: 40 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2339,6 +2339,43 @@ static Instruction *foldSelectGEP(GetElementPtrInst &GEP,
return SelectInst::Create(Cond, NewTrueC, NewFalseC, "", nullptr, Sel);
}

// Canonicalization:
// gep T, (gep i8, base, C1), (Index + C2) into
// gep T, (gep i8, base, C1 + C2 * sizeof(T)), Index
static Instruction *canonicalizeGEPOfConstGEPI8(GetElementPtrInst &GEP,
GEPOperator *Src,
InstCombinerImpl &IC) {
if (GEP.getNumIndices() != 1)
return nullptr;
auto &DL = IC.getDataLayout();
Value *Base;
const APInt *C1;
if (!match(Src, m_PtrAdd(m_Value(Base), m_APInt(C1))))
return nullptr;
Value *VarIndex;
const APInt *C2;
Type *PtrTy = Src->getType()->getScalarType();
unsigned IndexSizeInBits = DL.getIndexTypeSizeInBits(PtrTy);
if (!match(GEP.getOperand(1), m_AddLike(m_Value(VarIndex), m_APInt(C2))))
return nullptr;
if (C1->getBitWidth() != IndexSizeInBits ||
C2->getBitWidth() != IndexSizeInBits)
return nullptr;
Type *BaseType = GEP.getSourceElementType();
if (isa<ScalableVectorType>(BaseType))
return nullptr;
APInt TypeSize(IndexSizeInBits, DL.getTypeAllocSize(BaseType));
APInt NewOffset = TypeSize * *C2 + *C1;
if (NewOffset.isZero() ||
(Src->hasOneUse() && GEP.getOperand(1)->hasOneUse())) {
Value *GEPConst =
IC.Builder.CreatePtrAdd(Base, IC.Builder.getInt(NewOffset));
return GetElementPtrInst::Create(BaseType, GEPConst, VarIndex);
}

return nullptr;
}

Instruction *InstCombinerImpl::visitGEPOfGEP(GetElementPtrInst &GEP,
GEPOperator *Src) {
// Combine Indices - If the source pointer to this getelementptr instruction
Expand All @@ -2347,6 +2384,9 @@ Instruction *InstCombinerImpl::visitGEPOfGEP(GetElementPtrInst &GEP,
if (!shouldMergeGEPs(*cast<GEPOperator>(&GEP), *Src))
return nullptr;

if (auto *I = canonicalizeGEPOfConstGEPI8(GEP, Src, *this))
return I;

// For constant GEPs, use a more general offset-based folding approach.
Type *PtrTy = Src->getType()->getScalarType();
if (GEP.hasAllConstantIndices() &&
Expand Down
292 changes: 292 additions & 0 deletions llvm/test/Transforms/InstCombine/gepofconstgepi8.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,292 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
; RUN: opt < %s -S -passes=instcombine | FileCheck %s

declare void @use64(i64)
declare void @useptr(ptr)

define ptr @test_zero(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_zero(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[BASE]], i64 [[A]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_nonzero(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_nonzero(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i8, ptr [[BASE]], i64 4
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[TMP0]], i64 [[A]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i64 %a, 2
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_or_disjoint(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_or_disjoint(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[BASE]], i64 [[A]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = or disjoint i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_zero_multiuse_index(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_zero_multiuse_index(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[INDEX:%.*]] = add i64 [[A]], 1
; CHECK-NEXT: call void @use64(i64 [[INDEX]])
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[BASE]], i64 [[A]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i64 %a, 1
call void @use64(i64 %index)
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_zero_multiuse_ptr(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_zero_multiuse_ptr(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: call void @useptr(ptr [[P1]])
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[BASE]], i64 [[A]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
call void @useptr(ptr %p1)
%index = add i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_zero_sext_add_nsw(ptr %base, i32 %a) {
; CHECK-LABEL: define ptr @test_zero_sext_add_nsw(
; CHECK-SAME: ptr [[BASE:%.*]], i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[TMP0:%.*]] = sext i32 [[A]] to i64
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i32, ptr [[P1]], i64 [[TMP0]]
; CHECK-NEXT: [[P2:%.*]] = getelementptr i8, ptr [[TMP1]], i64 4
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add nsw i32 %a, 1
%p2 = getelementptr i32, ptr %p1, i32 %index
ret ptr %p2
}

define ptr @test_zero_trunc_add(ptr %base, i128 %a) {
; CHECK-LABEL: define ptr @test_zero_trunc_add(
; CHECK-SAME: ptr [[BASE:%.*]], i128 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TMP0:%.*]] = trunc i128 [[A]] to i64
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[BASE]], i64 [[TMP0]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i128 %a, 1
%p2 = getelementptr i32, ptr %p1, i128 %index
ret ptr %p2
}

define ptr @test_non_i8(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_non_i8(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
; CHECK-NEXT: ret ptr [[TMP0]]
;
entry:
%p1 = getelementptr i16, ptr %base, i64 -4
%index = add i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_non_const(ptr %base, i64 %a, i64 %b) {
; CHECK-LABEL: define ptr @test_non_const(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 [[B]]
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
; CHECK-NEXT: [[P2:%.*]] = getelementptr i8, ptr [[TMP0]], i64 4
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 %b
%index = add i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_too_many_indices(ptr %base, i64 %a, i64 %b) {
; CHECK-LABEL: define ptr @test_too_many_indices(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 [[B]]
; CHECK-NEXT: [[INDEX:%.*]] = add i64 [[A]], 1
; CHECK-NEXT: [[P2:%.*]] = getelementptr [8 x i32], ptr [[P1]], i64 1, i64 [[INDEX]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 %b
%index = add i64 %a, 1
%p2 = getelementptr [8 x i32], ptr %p1, i64 1, i64 %index
ret ptr %p2
}

define ptr @test_wrong_op(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_wrong_op(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[INDEX:%.*]] = xor i64 [[A]], 1
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[P1]], i64 [[INDEX]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = xor i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_sext_add_without_nsw(ptr %base, i32 %a) {
; CHECK-LABEL: define ptr @test_sext_add_without_nsw(
; CHECK-SAME: ptr [[BASE:%.*]], i32 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[INDEX:%.*]] = add i32 [[A]], 1
; CHECK-NEXT: [[TMP0:%.*]] = sext i32 [[INDEX]] to i64
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[P1]], i64 [[TMP0]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i32 %a, 1
%p2 = getelementptr i32, ptr %p1, i32 %index
ret ptr %p2
}

define ptr @test_or_without_disjoint(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_or_without_disjoint(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[INDEX:%.*]] = or i64 [[A]], 1
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[P1]], i64 [[INDEX]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = or i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_smul_overflow(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_smul_overflow(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -12
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
; CHECK-NEXT: ret ptr [[TMP0]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i64 %a, 9223372036854775806
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_sadd_overflow(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_sadd_overflow(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -9223372036854775808
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
; CHECK-NEXT: ret ptr [[TMP0]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 9223372036854775804
%index = add i64 %a, 1
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_nonzero_multiuse_index(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_nonzero_multiuse_index(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[INDEX:%.*]] = add i64 [[A]], 2
; CHECK-NEXT: call void @use64(i64 [[INDEX]])
; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[P1]], i64 [[INDEX]]
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i64 %a, 2
call void @use64(i64 %index)
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_nonzero_multiuse_ptr(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_nonzero_multiuse_ptr(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: call void @useptr(ptr [[P1]])
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
; CHECK-NEXT: [[P2:%.*]] = getelementptr i8, ptr [[TMP0]], i64 8
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
call void @useptr(ptr %p1)
%index = add i64 %a, 2
%p2 = getelementptr i32, ptr %p1, i64 %index
ret ptr %p2
}

define ptr @test_scalable(ptr %base, i64 %a) {
; CHECK-LABEL: define ptr @test_scalable(
; CHECK-SAME: ptr [[BASE:%.*]], i64 [[A:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[P1:%.*]] = getelementptr i8, ptr [[BASE]], i64 -4
; CHECK-NEXT: [[TMP0:%.*]] = getelementptr <vscale x 4 x i32>, ptr [[P1]], i64 [[A]]
; CHECK-NEXT: [[P2:%.*]] = getelementptr <vscale x 4 x i32>, ptr [[TMP0]], i64 1
; CHECK-NEXT: ret ptr [[P2]]
;
entry:
%p1 = getelementptr i8, ptr %base, i64 -4
%index = add i64 %a, 1
%p2 = getelementptr <vscale x 4 x i32>, ptr %p1, i64 %index
ret ptr %p2
}

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