[InstCombine] Canonicalize gep T, (gep i8, base, C1), (Index + C2) into gep T, (gep i8, base, C1 + C2 * sizeof(T)), Index
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@llvm/pr-subscribers-llvm-transforms Author: Yingwei Zheng (dtcxzyw) ChangesThis patch tries to canonicalize Alive2: https://alive2.llvm.org/ce/z/9icv7n Note: I found that Full diff: https://github.com/llvm/llvm-project/pull/76177.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 775720ab43a5c0..bfa208cc4dda5e 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -2038,6 +2038,54 @@ static Instruction *foldSelectGEP(GetElementPtrInst &GEP,
return SelectInst::Create(Cond, NewTrueC, NewFalseC, "", nullptr, Sel);
}
+// Canonicalization:
+// gep T, (gep i8, base, C1), (Index +nsw 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();
+ if (!Src->getSourceElementType()->isIntegerTy(8) ||
+ !Src->hasAllConstantIndices())
+ return nullptr;
+ Value *VarIndex;
+ const APInt *C2;
+ Type *PtrTy = Src->getType()->getScalarType();
+ unsigned IndexSizeInBits = DL.getIndexTypeSizeInBits(PtrTy);
+ if (!(GEP.getOperand(1)->getType()->getScalarSizeInBits() >=
+ IndexSizeInBits &&
+ match(GEP.getOperand(1), m_Add(m_Value(VarIndex), m_APInt(C2)))) &&
+ !match(GEP.getOperand(1),
+ m_SExtOrSelf(
+ m_CombineOr(m_NSWAdd(m_Value(VarIndex), m_APInt(C2)),
+ m_DisjointOr(m_Value(VarIndex), m_APInt(C2))))))
+ return nullptr;
+ Type *BaseType = GEP.getSourceElementType();
+ APInt C1(IndexSizeInBits, 0);
+ // Add the offset for Src (which is fully constant).
+ if (!Src->accumulateConstantOffset(DL, C1))
+ return nullptr;
+ APInt TypeSize(IndexSizeInBits, DL.getTypeAllocSize(BaseType));
+ bool Overflow = false;
+ APInt C3 = TypeSize.smul_ov(C2->sext(TypeSize.getBitWidth()), Overflow);
+ if (Overflow)
+ return nullptr;
+ APInt NewOffset = C1.sadd_ov(C3, Overflow);
+ if (Overflow)
+ return nullptr;
+ if (NewOffset.isZero() ||
+ (Src->hasOneUse() && GEP.getOperand(1)->hasOneUse())) {
+ Value *GEPConst =
+ IC.Builder.CreateGEP(IC.Builder.getInt8Ty(), Src->getPointerOperand(),
+ 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
@@ -2046,6 +2094,9 @@ 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() &&
diff --git a/llvm/test/Transforms/InstCombine/gepofconstgepi8.ll b/llvm/test/Transforms/InstCombine/gepofconstgepi8.ll
new file mode 100644
index 00000000000000..0d280f0055748c
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/gepofconstgepi8.ll
@@ -0,0 +1,282 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -S -passes=instcombine | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+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: [[TMP0:%.*]] = sext i32 [[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 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
+}
+
+; Negative tests
+
+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 i16, ptr [[BASE]], i64 -4
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
+; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[TMP0]], i64 1
+; CHECK-NEXT: ret ptr [[P2]]
+;
+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 i32, ptr [[TMP0]], i64 1
+; 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 -4
+; CHECK-NEXT: [[INDEX:%.*]] = xor i64 [[A]], -9223372036854775808
+; 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, -9223372036854775808
+ %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 9223372036854775804
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr i32, ptr [[P1]], i64 [[A]]
+; CHECK-NEXT: [[P2:%.*]] = getelementptr i32, ptr [[TMP0]], i64 1
+; CHECK-NEXT: ret ptr [[P2]]
+;
+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 i32, ptr [[TMP0]], i64 2
+; 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
+}
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nikic
reviewed
Dec 21, 2023
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Note: I found that gep T, base, (Index +nsw C) will be expanded into gep T, (gep T, ptr, Index), C. Thus we can canonicalize the GEP of GEP by moving the constant-indexed GEP to the front/back. But in these regressions, the add inst is likely to be used by multiple users. So I think it is worth handling this pattern.
I think we should first make sure that the GEP of GEP representation folds, before implementing this for the less-canonical GEP of add representation.
nikic
reviewed
Apr 19, 2024
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gep T, (gep i8, base, C1), (Index +nsw C2) into gep T, (gep i8, base, C1 + C2 * sizeof(T)), Indexgep T, (gep i8, base, C1), (Index + C2) into gep T, (gep i8, base, C1 + C2 * sizeof(T)), Index
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This patch tries to canonicalize
gep T, (gep i8, base, C1), (Index + C2)intogep T, (gep i8, base, C1 + C2 * sizeof(T)), Index.Alive2: https://alive2.llvm.org/ce/z/dxShKF
Fixes regressions found in #68882.
Note: I found that
gep T, base, (Index +nsw C)will be expanded intogep T, (gep T, ptr, Index), C. Thus we can canonicalize the GEP of GEP by moving the constant-indexed GEP to the front/back. But in these regressions, theaddinst is likely to be used by multiple users. So I think it is worth handling this pattern.