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[GlobalISel] Combine (x op 0) -> x for operations with a right identity of 0
Implement identity combines for operations like the following: ``` %a = G_SUB %b, 0 ``` This can just be replaced with %b. Over CTMark, this gives some minor size improvements at -O3. Differential Revision: https://reviews.llvm.org/D76640
This commit is contained in:
Jessica Paquette
parent
e2e7135db3
commit
c18856f48a
@ -221,6 +221,10 @@ public:
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/// equivalent instructions.
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bool matchEqualDefs(const MachineOperand &MOP1, const MachineOperand &MOP2);
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/// Return true if \p MOP is defined by a G_CONSTANT with a value equal to
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/// \p C.
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bool matchConstantOp(const MachineOperand &MOP, int64_t C);
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/// Optimize (cond ? x : x) -> x
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bool matchSelectSameVal(MachineInstr &MI);
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@ -192,6 +192,14 @@ def select_same_val: GICombineRule<
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(apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, 2); }])
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>;
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// Fold x op 0 -> x
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def right_identity_zero: GICombineRule<
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(defs root:$root),
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(match (wip_match_opcode G_SUB, G_ADD, G_OR, G_XOR, G_SHL, G_ASHR, G_LSHR):$root,
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[{ return Helper.matchConstantOp(${root}->getOperand(2), 0); }]),
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(apply [{ return Helper.replaceSingleDefInstWithOperand(*${root}, 1); }])
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>;
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// FIXME: These should use the custom predicate feature once it lands.
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def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
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undef_to_negative_one,
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@ -199,7 +207,7 @@ def undef_combines : GICombineGroup<[undef_to_fp_zero, undef_to_int_zero,
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propagate_undef_all_ops,
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propagate_undef_shuffle_mask]>;
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def identity_combines : GICombineGroup<[select_same_val]>;
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def identity_combines : GICombineGroup<[select_same_val, right_identity_zero]>;
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def trivial_combines : GICombineGroup<[copy_prop, mul_to_shl]>;
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def all_combines : GICombineGroup<[trivial_combines, ptr_add_immed_chain,
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@ -9,6 +9,7 @@
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#include "llvm/CodeGen/GlobalISel/Combiner.h"
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#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
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#include "llvm/CodeGen/GlobalISel/GISelKnownBits.h"
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#include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
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#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
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#include "llvm/CodeGen/GlobalISel/Utils.h"
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#include "llvm/CodeGen/MachineDominators.h"
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@ -23,6 +24,7 @@
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#define DEBUG_TYPE "gi-combiner"
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using namespace llvm;
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using namespace MIPatternMatch;
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// Option to allow testing of the combiner while no targets know about indexed
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// addressing.
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@ -1546,6 +1548,13 @@ bool CombinerHelper::matchEqualDefs(const MachineOperand &MOP1,
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return Builder.getTII().produceSameValue(*I1, *I2, &MRI);
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}
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bool CombinerHelper::matchConstantOp(const MachineOperand &MOP, int64_t C) {
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if (!MOP.isReg())
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return false;
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int64_t Cst;
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return mi_match(MOP.getReg(), MRI, m_ICst(Cst)) && Cst == C;
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}
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bool CombinerHelper::replaceSingleDefInstWithOperand(MachineInstr &MI,
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unsigned OpIdx) {
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assert(MI.getNumExplicitDefs() == 1 && "Expected one explicit def?");
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@ -0,0 +1,163 @@
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# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
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# RUN: llc -mtriple aarch64 -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s
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name: right_ident_sub
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x - 0) -> x
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;
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; CHECK-LABEL: name: right_ident_sub
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_SUB %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: right_ident_add
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x + 0) -> x
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;
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; CHECK-LABEL: name: right_ident_add
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_ADD %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: right_ident_or
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x || 0) -> x
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;
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; CHECK-LABEL: name: right_ident_or
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_OR %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: right_ident_xor
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x | 0) -> x
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;
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; CHECK-LABEL: name: right_ident_xor
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_XOR %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: right_ident_shl
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x << 0) -> x
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;
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; CHECK-LABEL: name: right_ident_shl
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_SHL %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: right_ident_ashr
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x ashr 0) -> x
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;
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; CHECK-LABEL: name: right_ident_ashr
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_ASHR %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: right_ident_lshr
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Fold (x lshr 0) -> x
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;
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; CHECK-LABEL: name: right_ident_lshr
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: $w0 = COPY %x(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 0
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%op:_(s32) = G_LSHR %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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---
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name: dont_fold_sub
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tracksRegLiveness: true
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body: |
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bb.1.entry:
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liveins: $w0
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; Not an identity, no folding.
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;
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; CHECK-LABEL: name: dont_fold_sub
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; CHECK: liveins: $w0
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; CHECK: %x:_(s32) = COPY $w0
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; CHECK: %cst:_(s32) = G_CONSTANT i32 1
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; CHECK: %op:_(s32) = G_SUB %x, %cst
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; CHECK: $w0 = COPY %op(s32)
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; CHECK: RET_ReallyLR implicit $w0
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%x:_(s32) = COPY $w0
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%cst:_(s32) = G_CONSTANT i32 1
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%op:_(s32) = G_SUB %x(s32), %cst
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$w0 = COPY %op(s32)
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RET_ReallyLR implicit $w0
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...
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