[llvm] [InstCombine] Remove shl if we only demand known signbits of shift source (PR #79014)
via llvm-commits
llvm-commits at lists.llvm.org
Mon Jan 22 09:20:26 PST 2024
https://github.com/ParkHanbum created https://github.com/llvm/llvm-project/pull/79014
this patch resolve TODO written in commit
https://github.com/llvm/llvm-project/commit/5909c678831f3a5c1669f6906f777d4ec4532fa1
>From 8c3412097cbc71a4813caf61f2ecbf9933c9d0f4 Mon Sep 17 00:00:00 2001
From: Hanbum Park <kese111 at gmail.com>
Date: Tue, 23 Jan 2024 01:38:18 +0900
Subject: [PATCH 1/2] [InstCombine] Add test for removing shl if we only demand
known signbits of shift
---
.../test/Transforms/InstCombine/shl-demand.ll | 121 ++++++++++++++++++
1 file changed, 121 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/shl-demand.ll b/llvm/test/Transforms/InstCombine/shl-demand.ll
index 85752890b4b80da..024d31c32c8d621 100644
--- a/llvm/test/Transforms/InstCombine/shl-demand.ll
+++ b/llvm/test/Transforms/InstCombine/shl-demand.ll
@@ -1,6 +1,127 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+; If we only want bits that already match the signbit then we don't need to shift.
+; https://alive2.llvm.org/ce/z/WJBPVt
+define i32 @src_srem_shl_demand_max_signbit(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_max_signbit(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 2
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 30
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -2147483648
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 2 ; srem = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSD
+ %shl = shl i32 %srem, 30 ; shl = SD000000000000000000000000000000
+ %mask = and i32 %shl, -2147483648 ; mask = 10000000000000000000000000000000
+ ret i32 %mask
+}
+
+define i32 @src_srem_shl_demand_min_signbit(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_min_signbit(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 1073741823
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -2147483648
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 1073741823 ; srem = SSDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
+ %shl = shl i32 %srem, 1 ; shl = SDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD0
+ %mask = and i32 %shl, -2147483648 ; mask = 10000000000000000000000000000000
+ ret i32 %mask
+}
+
+define i32 @src_srem_shl_demand_max_mask(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_max_mask(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 2
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -4
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 2 ; srem = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSD
+ %shl = shl i32 %srem, 1 ; shl = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSD0
+ %mask = and i32 %shl, -4 ; mask = 11111111111111111111111111111100
+ ret i32 %mask
+}
+
+; Negative test - mask demands non-signbit from shift source
+define i32 @src_srem_shl_demand_max_signbit_mask_hit_first_demand(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_max_signbit_mask_hit_first_demand(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 4
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 29
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -1073741824
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 4 ; srem = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSDD
+ %shl = shl i32 %srem, 29 ; shl = SDD00000000000000000000000000000
+ %mask = and i32 %shl, -1073741824 ; mask = 11000000000000000000000000000000
+ ret i32 %mask
+}
+
+define i32 @src_srem_shl_demand_min_signbit_mask_hit_last_demand(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_min_signbit_mask_hit_last_demand(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 536870912
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -1073741822
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 536870912 ; srem = SSSDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
+ %shl = shl i32 %srem, 1 ; shl = SSDDDDDDDDDDDDDDDDDDDDDDDDDDDDD0
+ %mask = and i32 %shl, -1073741822 ; mask = 11000000000000000000000000000010
+ ret i32 %mask
+}
+
+define i32 @src_srem_shl_demand_eliminate_signbit(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_eliminate_signbit(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 1073741824
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], 2
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 1073741824 ; srem = SSDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
+ %shl = shl i32 %srem, 1 ; shl = DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD0
+ %mask = and i32 %shl, 2 ; mask = 00000000000000000000000000000010
+ ret i32 %mask
+}
+
+define i32 @src_srem_shl_demand_max_mask_hit_demand(i32 %a0) {
+; CHECK-LABEL: @src_srem_shl_demand_max_mask_hit_demand(
+; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 4
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -4
+; CHECK-NEXT: ret i32 [[MASK]]
+;
+ %srem = srem i32 %a0, 4 ; srem = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSDD
+ %shl= shl i32 %srem, 1 ; shl = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSDD0
+ %mask = and i32 %shl, -4 ; mask = 11111111111111111111111111111100
+ ret i32 %mask
+}
+
+define <2 x i32> @src_srem_shl_mask_vector(<2 x i32> %a0) {
+; CHECK-LABEL: @src_srem_shl_mask_vector(
+; CHECK-NEXT: [[SREM:%.*]] = srem <2 x i32> [[A0:%.*]], <i32 4, i32 4>
+; CHECK-NEXT: [[SHL:%.*]] = shl nsw <2 x i32> [[SREM]], <i32 29, i32 29>
+; CHECK-NEXT: [[MASK:%.*]] = and <2 x i32> [[SHL]], <i32 -1073741824, i32 -1073741824>
+; CHECK-NEXT: ret <2 x i32> [[MASK]]
+;
+ %srem = srem <2 x i32> %a0, <i32 4, i32 4>
+ %shl = shl <2 x i32> %srem, <i32 29, i32 29>
+ %mask = and <2 x i32> %shl, <i32 -1073741824, i32 -1073741824>
+ ret <2 x i32> %mask
+}
+
+define <2 x i32> @src_srem_shl_mask_vector_nonconstant(<2 x i32> %a0, <2 x i32> %a1) {
+; CHECK-LABEL: @src_srem_shl_mask_vector_nonconstant(
+; CHECK-NEXT: [[SREM:%.*]] = srem <2 x i32> [[A0:%.*]], <i32 4, i32 4>
+; CHECK-NEXT: [[SHL:%.*]] = shl <2 x i32> [[SREM]], [[A1:%.*]]
+; CHECK-NEXT: [[MASK:%.*]] = and <2 x i32> [[SHL]], <i32 -1073741824, i32 -1073741824>
+; CHECK-NEXT: ret <2 x i32> [[MASK]]
+;
+ %srem = srem <2 x i32> %a0, <i32 4, i32 4>
+ %shl = shl <2 x i32> %srem, %a1
+ %mask = and <2 x i32> %shl, <i32 -1073741824, i32 -1073741824>
+ ret <2 x i32> %mask
+}
+
define i16 @sext_shl_trunc_same_size(i16 %x, i32 %y) {
; CHECK-LABEL: @sext_shl_trunc_same_size(
; CHECK-NEXT: [[CONV1:%.*]] = zext i16 [[X:%.*]] to i32
>From 011f822b9bc6b945b5228f5759d35939477ed6f8 Mon Sep 17 00:00:00 2001
From: Hanbum Park <kese111 at gmail.com>
Date: Tue, 23 Jan 2024 01:42:50 +0900
Subject: [PATCH 2/2] [InstCombine] Remove shl if we only demand known signbits
of shift source
this patch resolve TODO written in commit
5909c678831f3a5c1669f6906f777d4ec4532fa1
proof: https://alive2.llvm.org/ce/z/WJBPVt
---
.../InstCombineSimplifyDemanded.cpp | 40 +++++++++++--------
.../test/Transforms/InstCombine/shl-demand.ll | 9 ++---
2 files changed, 26 insertions(+), 23 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index a8a5f9831e15e3a..6ef00bab5307ec4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -640,25 +640,31 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
DemandedMask, Known))
return R;
- // TODO: If we only want bits that already match the signbit then we don't
+ uint64_t ShiftAmt = SA->getLimitedValue(BitWidth - 1);
+ // If we only want bits that already match the signbit then we don't
// need to shift.
+ if (DemandedMask.countr_zero() >= ShiftAmt) {
+ unsigned NumLowDemandedBits = BitWidth - DemandedMask.countr_zero();
+ unsigned SignBits =
+ ComputeNumSignBits(I->getOperand(0), Depth + 1, CxtI);
+ if (SignBits > ShiftAmt && SignBits - ShiftAmt >= NumLowDemandedBits)
+ return I->getOperand(0);
- // If we can pre-shift a right-shifted constant to the left without
- // losing any high bits amd we don't demand the low bits, then eliminate
- // the left-shift:
- // (C >> X) << LeftShiftAmtC --> (C << RightShiftAmtC) >> X
- uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
- Value *X;
- Constant *C;
- if (DemandedMask.countr_zero() >= ShiftAmt &&
- match(I->getOperand(0), m_LShr(m_ImmConstant(C), m_Value(X)))) {
- Constant *LeftShiftAmtC = ConstantInt::get(VTy, ShiftAmt);
- Constant *NewC = ConstantFoldBinaryOpOperands(Instruction::Shl, C,
- LeftShiftAmtC, DL);
- if (ConstantFoldBinaryOpOperands(Instruction::LShr, NewC, LeftShiftAmtC,
- DL) == C) {
- Instruction *Lshr = BinaryOperator::CreateLShr(NewC, X);
- return InsertNewInstWith(Lshr, I->getIterator());
+ // If we can pre-shift a right-shifted constant to the left without
+ // losing any high bits amd we don't demand the low bits, then eliminate
+ // the left-shift:
+ // (C >> X) << LeftShiftAmtC --> (C << RightShiftAmtC) >> X
+ Value *X;
+ Constant *C;
+ if (match(I->getOperand(0), m_LShr(m_ImmConstant(C), m_Value(X)))) {
+ Constant *LeftShiftAmtC = ConstantInt::get(VTy, ShiftAmt);
+ Constant *NewC = ConstantFoldBinaryOpOperands(Instruction::Shl, C,
+ LeftShiftAmtC, DL);
+ if (ConstantFoldBinaryOpOperands(Instruction::LShr, NewC,
+ LeftShiftAmtC, DL) == C) {
+ Instruction *Lshr = BinaryOperator::CreateLShr(NewC, X);
+ return InsertNewInstWith(Lshr, I->getIterator());
+ }
}
}
diff --git a/llvm/test/Transforms/InstCombine/shl-demand.ll b/llvm/test/Transforms/InstCombine/shl-demand.ll
index 024d31c32c8d621..26175ebbe153588 100644
--- a/llvm/test/Transforms/InstCombine/shl-demand.ll
+++ b/llvm/test/Transforms/InstCombine/shl-demand.ll
@@ -7,8 +7,7 @@
define i32 @src_srem_shl_demand_max_signbit(i32 %a0) {
; CHECK-LABEL: @src_srem_shl_demand_max_signbit(
; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 2
-; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 30
-; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -2147483648
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SREM]], -2147483648
; CHECK-NEXT: ret i32 [[MASK]]
;
%srem = srem i32 %a0, 2 ; srem = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSD
@@ -20,8 +19,7 @@ define i32 @src_srem_shl_demand_max_signbit(i32 %a0) {
define i32 @src_srem_shl_demand_min_signbit(i32 %a0) {
; CHECK-LABEL: @src_srem_shl_demand_min_signbit(
; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 1073741823
-; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
-; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -2147483648
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SREM]], -2147483648
; CHECK-NEXT: ret i32 [[MASK]]
;
%srem = srem i32 %a0, 1073741823 ; srem = SSDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
@@ -33,8 +31,7 @@ define i32 @src_srem_shl_demand_min_signbit(i32 %a0) {
define i32 @src_srem_shl_demand_max_mask(i32 %a0) {
; CHECK-LABEL: @src_srem_shl_demand_max_mask(
; CHECK-NEXT: [[SREM:%.*]] = srem i32 [[A0:%.*]], 2
-; CHECK-NEXT: [[SHL:%.*]] = shl nsw i32 [[SREM]], 1
-; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SHL]], -4
+; CHECK-NEXT: [[MASK:%.*]] = and i32 [[SREM]], -4
; CHECK-NEXT: ret i32 [[MASK]]
;
%srem = srem i32 %a0, 2 ; srem = SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSD
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