[llvm] [RDF] Create phi nodes for clobbering defs (PR #123694)
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Mon Jan 20 23:26:57 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-hexagon
Author: Yashas Andaluri (yandalur)
<details>
<summary>Changes</summary>
When a def in a block A reaches another block B that is in A's iterated dominance frontier, a phi node is added to B for the def register.
A clobbering def can be created at a call instruction, for a register clobbered by a call.
However, phi nodes are not created for a register, when one of the reaching defs of the register is a clobbering def.
This patch adds phi nodes for registers that have a clobbering reaching def. These additional phis help in checking reaching defs for an instruction in RDF based copy propagation and addressing mode optimizations.
---
Full diff: https://github.com/llvm/llvm-project/pull/123694.diff
4 Files Affected:
- (modified) llvm/include/llvm/CodeGen/RDFGraph.h (+4-3)
- (modified) llvm/lib/CodeGen/RDFGraph.cpp (+55-7)
- (added) llvm/test/CodeGen/Hexagon/rdf-copy-clobber.mir (+143)
- (added) llvm/test/CodeGen/Hexagon/rdf-phi-clobber.mir (+102)
``````````diff
diff --git a/llvm/include/llvm/CodeGen/RDFGraph.h b/llvm/include/llvm/CodeGen/RDFGraph.h
index cf7344e8c3e746..8a93afbcb54914 100644
--- a/llvm/include/llvm/CodeGen/RDFGraph.h
+++ b/llvm/include/llvm/CodeGen/RDFGraph.h
@@ -865,8 +865,9 @@ struct DataFlowGraph {
using BlockRefsMap = RegisterAggrMap<NodeId>;
void buildStmt(Block BA, MachineInstr &In);
- void recordDefsForDF(BlockRefsMap &PhiM, Block BA);
- void buildPhis(BlockRefsMap &PhiM, Block BA);
+ void recordDefsForDF(BlockRefsMap &PhiM, BlockRefsMap &PhiClobberM, Block BA);
+ void buildPhis(BlockRefsMap &PhiM, Block BA,
+ const DefStackMap &DefM = DefStackMap());
void removeUnusedPhis();
void pushClobbers(Instr IA, DefStackMap &DM);
@@ -874,7 +875,7 @@ struct DataFlowGraph {
template <typename T> void linkRefUp(Instr IA, NodeAddr<T> TA, DefStack &DS);
template <typename Predicate>
void linkStmtRefs(DefStackMap &DefM, Stmt SA, Predicate P);
- void linkBlockRefs(DefStackMap &DefM, Block BA);
+ void linkBlockRefs(DefStackMap &DefM, BlockRefsMap &PhiClobberM, Block BA);
void unlinkUseDF(Use UA);
void unlinkDefDF(Def DA);
diff --git a/llvm/lib/CodeGen/RDFGraph.cpp b/llvm/lib/CodeGen/RDFGraph.cpp
index 483e61db788f46..805b0ee7be0bc6 100644
--- a/llvm/lib/CodeGen/RDFGraph.cpp
+++ b/llvm/lib/CodeGen/RDFGraph.cpp
@@ -966,15 +966,18 @@ void DataFlowGraph::build(const Config &config) {
// Build a map "PhiM" which will contain, for each block, the set
// of references that will require phi definitions in that block.
+ // "PhiClobberM" map contains references that require phis for clobbering defs
BlockRefsMap PhiM(getPRI());
+ BlockRefsMap PhiClobberM(getPRI());
for (Block BA : Blocks)
- recordDefsForDF(PhiM, BA);
+ recordDefsForDF(PhiM, PhiClobberM, BA);
for (Block BA : Blocks)
buildPhis(PhiM, BA);
// Link all the refs. This will recursively traverse the dominator tree.
+ // Phis for clobbering defs are added here.
DefStackMap DM;
- linkBlockRefs(DM, EA);
+ linkBlockRefs(DM, PhiClobberM, EA);
// Finally, remove all unused phi nodes.
if (!(BuildCfg.Options & BuildOptions::KeepDeadPhis))
@@ -1378,7 +1381,9 @@ void DataFlowGraph::buildStmt(Block BA, MachineInstr &In) {
// Scan all defs in the block node BA and record in PhiM the locations of
// phi nodes corresponding to these defs.
-void DataFlowGraph::recordDefsForDF(BlockRefsMap &PhiM, Block BA) {
+// Clobbering defs in BA are recorded in PhiClobberM
+void DataFlowGraph::recordDefsForDF(BlockRefsMap &PhiM,
+ BlockRefsMap &PhiClobberM, Block BA) {
// Check all defs from block BA and record them in each block in BA's
// iterated dominance frontier. This information will later be used to
// create phi nodes.
@@ -1394,11 +1399,17 @@ void DataFlowGraph::recordDefsForDF(BlockRefsMap &PhiM, Block BA) {
// This is done to make sure that each defined reference gets only one
// phi node, even if it is defined multiple times.
RegisterAggr Defs(getPRI());
+ RegisterAggr ClobberDefs(getPRI());
for (Instr IA : BA.Addr->members(*this)) {
for (Ref RA : IA.Addr->members_if(IsDef, *this)) {
RegisterRef RR = RA.Addr->getRegRef(*this);
- if (RR.isReg() && isTracked(RR))
+ if (!isTracked(RR))
+ continue;
+ if (RR.isReg())
Defs.insert(RR);
+ // Clobbering def
+ else if (RR.isMask())
+ ClobberDefs.insert(RR);
}
}
@@ -1416,12 +1427,14 @@ void DataFlowGraph::recordDefsForDF(BlockRefsMap &PhiM, Block BA) {
for (auto *DB : IDF) {
Block DBA = findBlock(DB);
PhiM[DBA.Id].insert(Defs);
+ PhiClobberM[DBA.Id].insert(ClobberDefs);
}
}
// Given the locations of phi nodes in the map PhiM, create the phi nodes
// that are located in the block node BA.
-void DataFlowGraph::buildPhis(BlockRefsMap &PhiM, Block BA) {
+void DataFlowGraph::buildPhis(BlockRefsMap &PhiM, Block BA,
+ const DefStackMap &DefM) {
// Check if this blocks has any DF defs, i.e. if there are any defs
// that this block is in the iterated dominance frontier of.
auto HasDF = PhiM.find(BA.Id);
@@ -1434,10 +1447,37 @@ void DataFlowGraph::buildPhis(BlockRefsMap &PhiM, Block BA) {
for (MachineBasicBlock *PB : MBB->predecessors())
Preds.push_back(findBlock(PB));
+ RegisterAggr PhiDefs(getPRI());
+ // DefM will be non empty when we are building phis
+ // for clobbering defs
+ if (!DefM.empty()) {
+ for (Instr IA : BA.Addr->members_if(IsPhi, *this)) {
+ for (Def DA : IA.Addr->members_if(IsDef, *this)) {
+ auto DR = DA.Addr->getRegRef(*this);
+ PhiDefs.insert(DR);
+ }
+ }
+ }
+
+ MachineRegisterInfo &MRI = MF.getRegInfo();
const RegisterAggr &Defs = PhiM[BA.Id];
uint16_t PhiFlags = NodeAttrs::PhiRef | NodeAttrs::Preserving;
for (RegisterRef RR : Defs.refs()) {
+ if (!DefM.empty()) {
+ auto F = DefM.find(RR.Reg);
+ // Do not create a phi for unallocatable registers, or for registers
+ // that are never livein to BA.
+ // If a phi exists for RR, do not create another.
+ if (!MRI.isAllocatable(RR.Reg) || PhiDefs.hasCoverOf(RR) ||
+ F == DefM.end() || F->second.empty())
+ continue;
+ // Do not create a phi, if all reaching defs are clobbering
+ auto RDef = F->second.top();
+ if (RDef->Addr->getFlags() & NodeAttrs::Clobbering)
+ continue;
+ PhiDefs.insert(RR);
+ }
Phi PA = newPhi(BA);
PA.Addr->addMember(newDef(PA, RR, PhiFlags), *this);
@@ -1576,7 +1616,15 @@ void DataFlowGraph::linkStmtRefs(DefStackMap &DefM, Stmt SA, Predicate P) {
// Create data-flow links for all instructions in the block node BA. This
// will include updating any phi nodes in BA.
-void DataFlowGraph::linkBlockRefs(DefStackMap &DefM, Block BA) {
+void DataFlowGraph::linkBlockRefs(DefStackMap &DefM, BlockRefsMap &PhiClobberM,
+ Block BA) {
+ // Create phi nodes for clobbering defs.
+ // Since a huge number of registers can get clobbered, it would result in many
+ // phi nodes being created in the graph. Only create phi nodes that have a non
+ // clobbering reaching def. Use DefM to get not clobbering defs reaching a
+ // block.
+ buildPhis(PhiClobberM, BA, DefM);
+
// Push block delimiters.
markBlock(BA.Id, DefM);
@@ -1613,7 +1661,7 @@ void DataFlowGraph::linkBlockRefs(DefStackMap &DefM, Block BA) {
for (auto *I : *N) {
MachineBasicBlock *SB = I->getBlock();
Block SBA = findBlock(SB);
- linkBlockRefs(DefM, SBA);
+ linkBlockRefs(DefM, PhiClobberM, SBA);
}
// Link the phi uses from the successor blocks.
diff --git a/llvm/test/CodeGen/Hexagon/rdf-copy-clobber.mir b/llvm/test/CodeGen/Hexagon/rdf-copy-clobber.mir
new file mode 100644
index 00000000000000..e0676a143eefe3
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/rdf-copy-clobber.mir
@@ -0,0 +1,143 @@
+# RUN: llc -march=hexagon -run-pass=hexagon-rdf-opt -hexagon-rdf-dump -verify-machineinstrs -o /dev/null %s 2>&1 | FileCheck %s
+
+# Check that RDF graph has a phi node for R28 register in bb.3 and bb.4
+# R28 is clobbered by memcpy call. The clobbering def must be present in bb.4's IDF
+# This phi node should prevent $r27 from being replaced by $r28 by RDF copy propagation
+
+#CHECK-LABEL: Starting copy propagation on: foo
+
+#CHECK-LABEL: --- %bb.3 ---
+#CHECK: p{{[0-9]+}}: phi [+d{{[0-9]+}}<R28>
+
+#CHECK-LABEL: --- %bb.4 ---
+#CHECK: p{{[0-9]+}}: phi [+d{{[0-9]+}}<R28>
+
+#CHECK-LABEL: After Hexagon RDF optimizations
+#CHECK-LABEL: bb.3:
+#CHECK: renamable $r0 = A2_add renamable $r27
+
+--- |
+ define internal fastcc void @foo() unnamed_addr {
+ entry:
+ ret void
+ }
+
+ declare void @llvm.memcpy.p0.p0.i32(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i32, i1 immarg)
+
+---
+name: foo
+alignment: 16
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+callsEHReturn: false
+callsUnwindInit: false
+hasEHCatchret: false
+hasEHScopes: false
+hasEHFunclets: false
+isOutlined: false
+debugInstrRef: false
+failsVerification: false
+tracksDebugUserValues: true
+registers: []
+liveins:
+ - { reg: '$d0', virtual-reg: '' }
+ - { reg: '$d3', virtual-reg: '' }
+ - { reg: '$r23', virtual-reg: '' }
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 0
+ offsetAdjustment: 0
+ maxAlignment: 8
+ adjustsStack: true
+ hasCalls: true
+ stackProtector: ''
+ functionContext: ''
+ maxCallFrameSize: 4294967295
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ hasTailCall: false
+ isCalleeSavedInfoValid: false
+ localFrameSize: 0
+ savePoint: ''
+ restorePoint: ''
+fixedStack:
+ - { id: 0, type: default, offset: 40, size: 8, alignment: 8, stack-id: default,
+ isImmutable: true, isAliased: false, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+stack:
+ - { id: 0, name: '', type: spill-slot, offset: 0, size: 8, alignment: 8,
+ stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 1, name: '', type: spill-slot, offset: 0, size: 8, alignment: 8,
+ stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 2, name: '', type: spill-slot, offset: 0, size: 8, alignment: 8,
+ stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 3, name: '', type: spill-slot, offset: 0, size: 8, alignment: 8,
+ stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+entry_values: []
+callSites: []
+debugValueSubstitutions: []
+constants: []
+machineFunctionInfo: {}
+body: |
+ bb.0.entry:
+ successors: %bb.1
+ liveins: $d0, $d3, $r23
+
+ J2_jump %bb.1, implicit-def dead $pc
+
+ bb.1:
+ successors: %bb.2
+ liveins: $d0:0x0000000000000003, $d3:0x0000000000000003, $r23
+
+ renamable $r28 = L2_loadri_io %fixed-stack.0, 0 :: (load (s32) from %fixed-stack.0)
+ renamable $r27 = COPY killed renamable $r28
+
+ bb.2:
+ successors: %bb.3
+ liveins: $d0:0x0000000000000003, $d3:0x0000000000000003, $r23, $r27
+
+ renamable $d10 = L2_loadrd_io %stack.0, 0 :: (load (s64) from %stack.0)
+ renamable $d11 = L2_loadrd_io %stack.1, 0 :: (load (s64) from %stack.1)
+
+ bb.3:
+ successors: %bb.4, %bb.3
+ liveins: $d0:0x0000000000000003, $d3:0x0000000000000003, $d10:0x0000000000000003, $d11:0x0000000000000002, $r23, $r27
+
+ ADJCALLSTACKDOWN 0, 0, implicit-def $r29, implicit-def dead $r30, implicit $r31, implicit $r30, implicit $r29
+ renamable $r1 = A2_add renamable $r23, killed renamable $r0
+ $r2 = COPY renamable $r22
+ renamable $r0 = A2_add renamable $r27, killed renamable $r6
+ J2_call &memcpy, hexagoncsr, implicit-def dead $pc, implicit-def dead $r31, implicit $r29, implicit $r0, implicit $r1, implicit $r2, implicit-def $r29, implicit-def dead $r0
+ renamable $p0 = C2_cmpgtp renamable $d11, renamable $d10
+ ADJCALLSTACKUP 0, 0, implicit-def dead $r29, implicit-def dead $r30, implicit-def dead $r31, implicit $r29
+ J2_jumpt killed renamable $p0, %bb.3, implicit-def dead $pc
+ J2_jump %bb.4, implicit-def dead $pc
+
+ bb.4:
+ successors: %bb.5, %bb.2
+ liveins: $d10:0x0000000000000003, $d11:0x0000000000000002, $r23, $r27
+
+ renamable $d0 = L2_loadrd_io %stack.2, 0 :: (load (s64) from %stack.2)
+ renamable $d3 = L2_loadrd_io %stack.3, 0 :: (load (s64) from %stack.3)
+ renamable $p0 = C2_cmpgtp killed renamable $d0, killed renamable $d3
+ J2_jumpt killed renamable $p0, %bb.2, implicit-def dead $pc
+ J2_jump %bb.5, implicit-def dead $pc
+
+ bb.5:
+ PS_jmpret $r31, implicit-def dead $pc
+
+...
diff --git a/llvm/test/CodeGen/Hexagon/rdf-phi-clobber.mir b/llvm/test/CodeGen/Hexagon/rdf-phi-clobber.mir
new file mode 100644
index 00000000000000..d49cc3403d6441
--- /dev/null
+++ b/llvm/test/CodeGen/Hexagon/rdf-phi-clobber.mir
@@ -0,0 +1,102 @@
+# RUN: llc -march=hexagon -run-pass=hexagon-rdf-opt \
+# RUN: -hexagon-rdf-dump -verify-machineinstrs -o /dev/null %s 2>&1 \
+# RUN: | FileCheck %s
+
+# Check that phi nodes that only have clobbering reaching defs are not created
+# during graph construction. Check that there are no phi nodes for HVX registers
+
+#CHECK-LABEL: --- %bb.1 ---
+#CHECK-NOT: p{{[0-9]+}}: phi [+d{{[0-9]+}}<V{{[0-9]+}}>
+
+--- |
+ @.str.3 = private unnamed_addr constant [2 x i8] c"%d", align 8
+ @.str.4 = private unnamed_addr constant [2 x i8] c"%d", align 8
+
+ define internal fastcc void @foo() unnamed_addr {
+ entry:
+ ret void
+ }
+
+ declare dso_local noundef i32 @printf(ptr nocapture noundef readonly, ...) local_unnamed_addr
+
+---
+name: foo
+alignment: 16
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+callsEHReturn: false
+callsUnwindInit: false
+hasEHCatchret: false
+hasEHScopes: false
+hasEHFunclets: false
+isOutlined: false
+debugInstrRef: false
+failsVerification: false
+tracksDebugUserValues: true
+registers: []
+liveins:
+ - { reg: '$d0', virtual-reg: '' }
+ - { reg: '$d3', virtual-reg: '' }
+ - { reg: '$r23', virtual-reg: '' }
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 0
+ offsetAdjustment: 0
+ maxAlignment: 8
+ adjustsStack: true
+ hasCalls: true
+ stackProtector: ''
+ functionContext: ''
+ maxCallFrameSize: 4294967295
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ hasTailCall: false
+ isCalleeSavedInfoValid: false
+ localFrameSize: 0
+ savePoint: ''
+ restorePoint: ''
+entry_values: []
+callSites: []
+debugValueSubstitutions: []
+constants: []
+machineFunctionInfo: {}
+body: |
+ bb.0.entry:
+ successors: %bb.1
+ liveins: $r25, $r26, $d11
+
+ renamable $r16 = A2_tfrsi 0
+ S2_storerd_io $r29, 0, renamable $d11 :: (store (s64) into stack)
+ $r0 = A2_tfrsi @.str.3
+ J2_call @printf, hexagoncsr, implicit-def dead $pc, implicit-def dead $r31, implicit $r29, implicit $r0, implicit-def $r29, implicit-def dead $r0
+ J2_jump %bb.1, implicit-def dead $pc
+
+ bb.1:
+ successors: %bb.2, %bb.1
+ liveins: $r16, $r25, $r26
+
+ S2_storeri_io $r29, 0, killed renamable $r25 :: (store (s32) into stack)
+ $r0 = A2_tfrsi @.str.4
+ S2_storeri_io $r29, 8, killed renamable $r26 :: (store (s64) into stack + 8)
+ J2_call @printf, hexagoncsr, implicit-def dead $pc, implicit-def dead $r31, implicit $r29, implicit $r0, implicit-def $r29, implicit-def dead $r0
+ renamable $p0 = C2_cmpgti renamable $r16, 4
+ renamable $r16 = nsw A2_addi killed renamable $r16, 1
+ J2_jumpf killed renamable $p0, %bb.2, implicit-def dead $pc
+ J2_jump %bb.1, implicit-def dead $pc
+
+ bb.2:
+ liveins: $r16, $r25, $r26
+
+ PS_jmpret $r31, implicit-def dead $pc
+
+...
``````````
</details>
https://github.com/llvm/llvm-project/pull/123694
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