[llvm] [ConstantHoisting] Add a TTI hook to prevent hoisting. (PR #69004)
Paul Walker via llvm-commits
llvm-commits at lists.llvm.org
Wed Dec 13 05:10:56 PST 2023
https://github.com/paulwalker-arm updated https://github.com/llvm/llvm-project/pull/69004
>From f060d21ac7c44bf19d660c3c00e3b2042ca04b30 Mon Sep 17 00:00:00 2001
From: Paul Walker <paul.walker at arm.com>
Date: Fri, 13 Oct 2023 12:48:36 +0000
Subject: [PATCH 1/2] [ConstantHoisting] Add AArch64 tests for divide like
operations.
---
.../AArch64/large-immediate.ll | 129 ++++++++++++++++--
1 file changed, 120 insertions(+), 9 deletions(-)
diff --git a/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll b/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll
index 015f52157b9e7c..54a2bfb92d8315 100644
--- a/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll
+++ b/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll
@@ -1,27 +1,138 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
; RUN: opt -mtriple=arm64-darwin-unknown -S -passes=consthoist < %s | FileCheck %s
-define i128 @test1(i128 %a) nounwind {
-; CHECK-LABEL: test1
-; CHECK: %const = bitcast i128 12297829382473034410122878 to i128
+define i128 @test1(i128 %a) {
+; CHECK-LABEL: define i128 @test1(
+; CHECK-SAME: i128 [[A:%.*]]) {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i128 12297829382473034410122878 to i128
+; CHECK-NEXT: [[TMP1:%.*]] = add i128 [[A]], [[CONST]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i128 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i128 [[TMP2]]
+;
%1 = add i128 %a, 12297829382473034410122878
%2 = add i128 %1, 12297829382473034410122878
ret i128 %2
}
; Check that we don't hoist large, but cheap constants
-define i512 @test2(i512 %a) nounwind {
-; CHECK-LABEL: test2
-; CHECK-NOT: %const = bitcast i512 7 to i512
+define i512 @test2(i512 %a) {
+; CHECK-LABEL: define i512 @test2(
+; CHECK-SAME: i512 [[A:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = and i512 [[A]], 7
+; CHECK-NEXT: [[TMP2:%.*]] = or i512 [[TMP1]], 7
+; CHECK-NEXT: ret i512 [[TMP2]]
+;
%1 = and i512 %a, 7
%2 = or i512 %1, 7
ret i512 %2
}
; Check that we don't hoist the shift value of a shift instruction.
-define i512 @test3(i512 %a) nounwind {
-; CHECK-LABEL: test3
-; CHECK-NOT: %const = bitcast i512 504 to i512
+define i512 @test3(i512 %a) {
+; CHECK-LABEL: define i512 @test3(
+; CHECK-SAME: i512 [[A:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = shl i512 [[A]], 504
+; CHECK-NEXT: [[TMP2:%.*]] = ashr i512 [[TMP1]], 504
+; CHECK-NEXT: ret i512 [[TMP2]]
+;
%1 = shl i512 %a, 504
%2 = ashr i512 %1, 504
ret i512 %2
}
+
+; Ensure the code generator has the information necessary to simply sdiv.
+define i64 @sdiv(i64 %a) {
+; CHECK-LABEL: define i64 @sdiv(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv i64 [[A]], [[CONST]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i64 [[TMP2]]
+;
+ %1 = sdiv i64 %a, 4294967087
+ %2 = add i64 %1, 4294967087
+ ret i64 %2
+}
+
+; Ensure the code generator has the information necessary to simply srem.
+define i64 @srem(i64 %a) {
+; CHECK-LABEL: define i64 @srem(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
+; CHECK-NEXT: [[TMP1:%.*]] = srem i64 [[A]], [[CONST]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i64 [[TMP2]]
+;
+ %1 = srem i64 %a, 4294967087
+ %2 = add i64 %1, 4294967087
+ ret i64 %2
+}
+
+; Ensure the code generator has the information necessary to simply udiv.
+define i64 @udiv(i64 %a) {
+; CHECK-LABEL: define i64 @udiv(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
+; CHECK-NEXT: [[TMP1:%.*]] = udiv i64 [[A]], [[CONST]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i64 [[TMP2]]
+;
+ %1 = udiv i64 %a, 4294967087
+ %2 = add i64 %1, 4294967087
+ ret i64 %2
+}
+
+; Ensure the code generator has the information necessary to simply urem.
+define i64 @urem(i64 %a) {
+; CHECK-LABEL: define i64 @urem(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
+; CHECK-NEXT: [[TMP1:%.*]] = urem i64 [[A]], [[CONST]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i64 [[TMP2]]
+;
+ %1 = urem i64 %a, 4294967087
+ %2 = add i64 %1, 4294967087
+ ret i64 %2
+}
+
+; Code generator will not decompose divide like operations when the divisor is
+; no a constant.
+define i64 @sdiv_non_const_divisor(i64 %a) {
+; CHECK-LABEL: define i64 @sdiv_non_const_divisor(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv i64 [[CONST]], [[A]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i64 [[TMP2]]
+;
+ %1 = sdiv i64 4294967087, %a
+ %2 = add i64 %1, 4294967087
+ ret i64 %2
+}
+
+; Code generator emits divide instructions when optimising for size.
+define i64 @sdiv_minsize(i64 %a) minsize {
+; CHECK-LABEL: define i64 @sdiv_minsize(
+; CHECK-SAME: i64 [[A:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv i64 [[A]], [[CONST]]
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: ret i64 [[TMP2]]
+;
+ %1 = sdiv i64 %a, 4294967087
+ %2 = add i64 %1, 4294967087
+ ret i64 %2
+}
+
+define <2 x i64> @sdiv_v2i64(<2 x i64> %a) {
+; CHECK-LABEL: define <2 x i64> @sdiv_v2i64(
+; CHECK-SAME: <2 x i64> [[A:%.*]]) {
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv <2 x i64> [[A]], <i64 4294967087, i64 4294967087>
+; CHECK-NEXT: [[TMP2:%.*]] = add <2 x i64> [[TMP1]], <i64 4294967087, i64 4294967087>
+; CHECK-NEXT: ret <2 x i64> [[TMP2]]
+;
+ %1 = sdiv <2 x i64> %a, <i64 4294967087, i64 4294967087>
+ %2 = add <2 x i64> %1, <i64 4294967087, i64 4294967087>
+ ret <2 x i64> %2
+}
>From 119e13b61751fa513fb4093f75f1a7ee77aa5a2d Mon Sep 17 00:00:00 2001
From: Paul Walker <paul.walker at arm.com>
Date: Fri, 13 Oct 2023 12:48:55 +0100
Subject: [PATCH 2/2] [ConstantHoisting] Add a TTI hook to prevent hoisting.
Code generation can sometimes simplify expensive operations when
an operand is constant. An example of this is divides on AArch64
where they can be rewritten using a cheaper sequence of multiplies
and subtracts. Doing this is often better than hoisting expensive
constants which are likely to be hoisted by MachineLICM anyway.
---
.../llvm/Analysis/TargetTransformInfo.h | 16 +++++++++++++++
.../llvm/Analysis/TargetTransformInfoImpl.h | 5 +++++
llvm/include/llvm/CodeGen/BasicTTIImpl.h | 19 ++++++++++++++++++
llvm/lib/Analysis/TargetTransformInfo.cpp | 5 +++++
.../Transforms/Scalar/ConstantHoisting.cpp | 3 ++-
.../AArch64/large-immediate.ll | 20 ++++++++-----------
6 files changed, 55 insertions(+), 13 deletions(-)
diff --git a/llvm/include/llvm/Analysis/TargetTransformInfo.h b/llvm/include/llvm/Analysis/TargetTransformInfo.h
index fb6f3287e3d262..f5114fa40c70ad 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfo.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfo.h
@@ -1002,6 +1002,16 @@ class TargetTransformInfo {
/// more beneficial constant hoisting is).
InstructionCost getIntImmCodeSizeCost(unsigned Opc, unsigned Idx,
const APInt &Imm, Type *Ty) const;
+
+ /// It can be advantageous to detach complex constants from their uses to make
+ /// their generation cheaper. This hook allows targets to report when such
+ /// transformations might negatively effect the code generation of the
+ /// underlying operation. The motivating example is divides whereby hoisting
+ /// constants prevents the code generator's ability to transform them into
+ /// combinations of simpler operations.
+ bool preferToKeepConstantsAttached(const Instruction &Inst,
+ const Function &Fn) const;
+
/// @}
/// \name Vector Target Information
@@ -1873,6 +1883,8 @@ class TargetTransformInfo::Concept {
virtual InstructionCost getIntImmCostIntrin(Intrinsic::ID IID, unsigned Idx,
const APInt &Imm, Type *Ty,
TargetCostKind CostKind) = 0;
+ virtual bool preferToKeepConstantsAttached(const Instruction &Inst,
+ const Function &Fn) const = 0;
virtual unsigned getNumberOfRegisters(unsigned ClassID) const = 0;
virtual unsigned getRegisterClassForType(bool Vector,
Type *Ty = nullptr) const = 0;
@@ -2430,6 +2442,10 @@ class TargetTransformInfo::Model final : public TargetTransformInfo::Concept {
TargetCostKind CostKind) override {
return Impl.getIntImmCostIntrin(IID, Idx, Imm, Ty, CostKind);
}
+ bool preferToKeepConstantsAttached(const Instruction &Inst,
+ const Function &Fn) const override {
+ return Impl.preferToKeepConstantsAttached(Inst, Fn);
+ }
unsigned getNumberOfRegisters(unsigned ClassID) const override {
return Impl.getNumberOfRegisters(ClassID);
}
diff --git a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
index 5b612fd813067a..187412e987d304 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -427,6 +427,11 @@ class TargetTransformInfoImplBase {
return TTI::TCC_Free;
}
+ bool preferToKeepConstantsAttached(const Instruction &Inst,
+ const Function &Fn) const {
+ return true;
+ }
+
unsigned getNumberOfRegisters(unsigned ClassID) const { return 8; }
unsigned getRegisterClassForType(bool Vector, Type *Ty = nullptr) const {
diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
index e05ce2890a08c8..5e7bdcdf72a49f 100644
--- a/llvm/include/llvm/CodeGen/BasicTTIImpl.h
+++ b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -545,6 +545,25 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
return TargetTransformInfo::TCC_Expensive;
}
+ bool preferToKeepConstantsAttached(const Instruction &Inst,
+ const Function &Fn) const {
+ switch (Inst.getOpcode()) {
+ default:
+ break;
+ case Instruction::SDiv:
+ case Instruction::SRem:
+ case Instruction::UDiv:
+ case Instruction::URem: {
+ if (!isa<ConstantInt>(Inst.getOperand(1)))
+ return false;
+ EVT VT = getTLI()->getValueType(DL, Inst.getType());
+ return !getTLI()->isIntDivCheap(VT, Fn.getAttributes());
+ }
+ };
+
+ return false;
+ }
+
unsigned getInliningThresholdMultiplier() const { return 1; }
unsigned adjustInliningThreshold(const CallBase *CB) { return 0; }
unsigned getCallerAllocaCost(const CallBase *CB, const AllocaInst *AI) const {
diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
index 63b1b7567c8e9f..3f76dfdaac317c 100644
--- a/llvm/lib/Analysis/TargetTransformInfo.cpp
+++ b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -682,6 +682,11 @@ TargetTransformInfo::getIntImmCostIntrin(Intrinsic::ID IID, unsigned Idx,
return Cost;
}
+bool TargetTransformInfo::preferToKeepConstantsAttached(
+ const Instruction &Inst, const Function &Fn) const {
+ return TTIImpl->preferToKeepConstantsAttached(Inst, Fn);
+}
+
unsigned TargetTransformInfo::getNumberOfRegisters(unsigned ClassID) const {
return TTIImpl->getNumberOfRegisters(ClassID);
}
diff --git a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
index 3e5d979f11cc50..1fb9d7fff32f66 100644
--- a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
@@ -523,7 +523,8 @@ void ConstantHoistingPass::collectConstantCandidates(Function &Fn) {
if (!DT->isReachableFromEntry(&BB))
continue;
for (Instruction &Inst : BB)
- collectConstantCandidates(ConstCandMap, &Inst);
+ if (!TTI->preferToKeepConstantsAttached(Inst, Fn))
+ collectConstantCandidates(ConstCandMap, &Inst);
}
}
diff --git a/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll b/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll
index 54a2bfb92d8315..196a104adc0233 100644
--- a/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll
+++ b/llvm/test/Transforms/ConstantHoisting/AArch64/large-immediate.ll
@@ -44,9 +44,8 @@ define i512 @test3(i512 %a) {
define i64 @sdiv(i64 %a) {
; CHECK-LABEL: define i64 @sdiv(
; CHECK-SAME: i64 [[A:%.*]]) {
-; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
-; CHECK-NEXT: [[TMP1:%.*]] = sdiv i64 [[A]], [[CONST]]
-; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: [[TMP1:%.*]] = sdiv i64 [[A]], 4294967087
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], 4294967087
; CHECK-NEXT: ret i64 [[TMP2]]
;
%1 = sdiv i64 %a, 4294967087
@@ -58,9 +57,8 @@ define i64 @sdiv(i64 %a) {
define i64 @srem(i64 %a) {
; CHECK-LABEL: define i64 @srem(
; CHECK-SAME: i64 [[A:%.*]]) {
-; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
-; CHECK-NEXT: [[TMP1:%.*]] = srem i64 [[A]], [[CONST]]
-; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: [[TMP1:%.*]] = srem i64 [[A]], 4294967087
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], 4294967087
; CHECK-NEXT: ret i64 [[TMP2]]
;
%1 = srem i64 %a, 4294967087
@@ -72,9 +70,8 @@ define i64 @srem(i64 %a) {
define i64 @udiv(i64 %a) {
; CHECK-LABEL: define i64 @udiv(
; CHECK-SAME: i64 [[A:%.*]]) {
-; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
-; CHECK-NEXT: [[TMP1:%.*]] = udiv i64 [[A]], [[CONST]]
-; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: [[TMP1:%.*]] = udiv i64 [[A]], 4294967087
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], 4294967087
; CHECK-NEXT: ret i64 [[TMP2]]
;
%1 = udiv i64 %a, 4294967087
@@ -86,9 +83,8 @@ define i64 @udiv(i64 %a) {
define i64 @urem(i64 %a) {
; CHECK-LABEL: define i64 @urem(
; CHECK-SAME: i64 [[A:%.*]]) {
-; CHECK-NEXT: [[CONST:%.*]] = bitcast i64 4294967087 to i64
-; CHECK-NEXT: [[TMP1:%.*]] = urem i64 [[A]], [[CONST]]
-; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], [[CONST]]
+; CHECK-NEXT: [[TMP1:%.*]] = urem i64 [[A]], 4294967087
+; CHECK-NEXT: [[TMP2:%.*]] = add i64 [[TMP1]], 4294967087
; CHECK-NEXT: ret i64 [[TMP2]]
;
%1 = urem i64 %a, 4294967087
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