[llvm] RegAllocGreedy: Add dummy priority advisor for writing MIR tests (PR #121207)
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Fri Dec 27 04:24:15 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-regalloc
Author: Matt Arsenault (arsenm)
<details>
<summary>Changes</summary>
I regularly struggle reproducing failures in greedy due to changes
in priority when resuming the allocation from MIR vs. a complete
compilation starting at IR. That is, the fix in
e0919b189bf2df4f97f22ba40260ab5153988b14 did not really fix the
problem of the instruction distance mattering.
Add a way to bypass all of the priority heuristics for MIR tests,
by prioritizing only by virtual register number. Could also
give this a more specific name, like PrioritizeLowVirtRegNumber
---
Full diff: https://github.com/llvm/llvm-project/pull/121207.diff
4 Files Affected:
- (modified) llvm/lib/CodeGen/RegAllocGreedy.cpp (+6)
- (modified) llvm/lib/CodeGen/RegAllocPriorityAdvisor.cpp (+34-1)
- (modified) llvm/lib/CodeGen/RegAllocPriorityAdvisor.h (+13-1)
- (added) llvm/test/CodeGen/AMDGPU/dummy-regalloc-priority-advisor.mir (+54)
``````````diff
diff --git a/llvm/lib/CodeGen/RegAllocGreedy.cpp b/llvm/lib/CodeGen/RegAllocGreedy.cpp
index 4fa2bc76b38b4b..95a7801c372f7a 100644
--- a/llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ b/llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -376,6 +376,12 @@ unsigned DefaultPriorityAdvisor::getPriority(const LiveInterval &LI) const {
return Prio;
}
+unsigned DummyPriorityAdvisor::getPriority(const LiveInterval &LI) const {
+ // Prioritize by virtual register number, lowest first.
+ Register Reg = LI.reg();
+ return ~Reg.virtRegIndex();
+}
+
const LiveInterval *RAGreedy::dequeue() { return dequeue(Queue); }
const LiveInterval *RAGreedy::dequeue(PQueue &CurQueue) {
diff --git a/llvm/lib/CodeGen/RegAllocPriorityAdvisor.cpp b/llvm/lib/CodeGen/RegAllocPriorityAdvisor.cpp
index 0650aaff56ea00..4525b8fc5a383f 100644
--- a/llvm/lib/CodeGen/RegAllocPriorityAdvisor.cpp
+++ b/llvm/lib/CodeGen/RegAllocPriorityAdvisor.cpp
@@ -30,7 +30,10 @@ static cl::opt<RegAllocPriorityAdvisorAnalysis::AdvisorMode> Mode(
clEnumValN(RegAllocPriorityAdvisorAnalysis::AdvisorMode::Release,
"release", "precompiled"),
clEnumValN(RegAllocPriorityAdvisorAnalysis::AdvisorMode::Development,
- "development", "for training")));
+ "development", "for training"),
+ clEnumValN(
+ RegAllocPriorityAdvisorAnalysis::AdvisorMode::Dummy, "dummy",
+ "prioritize low virtual register numbers for test and debug")));
char RegAllocPriorityAdvisorAnalysis::ID = 0;
INITIALIZE_PASS(RegAllocPriorityAdvisorAnalysis, "regalloc-priority",
@@ -67,6 +70,31 @@ class DefaultPriorityAdvisorAnalysis final
}
const bool NotAsRequested;
};
+
+class DummyPriorityAdvisorAnalysis final
+ : public RegAllocPriorityAdvisorAnalysis {
+public:
+ DummyPriorityAdvisorAnalysis()
+ : RegAllocPriorityAdvisorAnalysis(AdvisorMode::Dummy) {}
+
+ // support for isa<> and dyn_cast.
+ static bool classof(const RegAllocPriorityAdvisorAnalysis *R) {
+ return R->getAdvisorMode() == AdvisorMode::Dummy;
+ }
+
+private:
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<SlotIndexesWrapperPass>();
+ RegAllocPriorityAdvisorAnalysis::getAnalysisUsage(AU);
+ }
+
+ std::unique_ptr<RegAllocPriorityAdvisor>
+ getAdvisor(const MachineFunction &MF, const RAGreedy &RA) override {
+ return std::make_unique<DummyPriorityAdvisor>(
+ MF, RA, &getAnalysis<SlotIndexesWrapperPass>().getSI());
+ }
+};
+
} // namespace
template <> Pass *llvm::callDefaultCtor<RegAllocPriorityAdvisorAnalysis>() {
@@ -75,6 +103,9 @@ template <> Pass *llvm::callDefaultCtor<RegAllocPriorityAdvisorAnalysis>() {
case RegAllocPriorityAdvisorAnalysis::AdvisorMode::Default:
Ret = new DefaultPriorityAdvisorAnalysis(/*NotAsRequested*/ false);
break;
+ case RegAllocPriorityAdvisorAnalysis::AdvisorMode::Dummy:
+ Ret = new DummyPriorityAdvisorAnalysis();
+ break;
case RegAllocPriorityAdvisorAnalysis::AdvisorMode::Development:
#if defined(LLVM_HAVE_TFLITE)
Ret = createDevelopmentModePriorityAdvisor();
@@ -97,6 +128,8 @@ StringRef RegAllocPriorityAdvisorAnalysis::getPassName() const {
return "Release mode Regalloc Priority Advisor";
case AdvisorMode::Development:
return "Development mode Regalloc Priority Advisor";
+ case AdvisorMode::Dummy:
+ return "Dummy Regalloc Priority Advisor";
}
llvm_unreachable("Unknown advisor kind");
}
diff --git a/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h b/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h
index 1e9fa967214cc8..32e4598b715392 100644
--- a/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h
+++ b/llvm/lib/CodeGen/RegAllocPriorityAdvisor.h
@@ -56,9 +56,21 @@ class DefaultPriorityAdvisor : public RegAllocPriorityAdvisor {
unsigned getPriority(const LiveInterval &LI) const override;
};
+/// Stupid priority advisor which just enqueues in virtual register number
+/// order, for debug purposes only.
+class DummyPriorityAdvisor : public RegAllocPriorityAdvisor {
+public:
+ DummyPriorityAdvisor(const MachineFunction &MF, const RAGreedy &RA,
+ SlotIndexes *const Indexes)
+ : RegAllocPriorityAdvisor(MF, RA, Indexes) {}
+
+private:
+ unsigned getPriority(const LiveInterval &LI) const override;
+};
+
class RegAllocPriorityAdvisorAnalysis : public ImmutablePass {
public:
- enum class AdvisorMode : int { Default, Release, Development };
+ enum class AdvisorMode : int { Default, Release, Development, Dummy };
RegAllocPriorityAdvisorAnalysis(AdvisorMode Mode)
: ImmutablePass(ID), Mode(Mode){};
diff --git a/llvm/test/CodeGen/AMDGPU/dummy-regalloc-priority-advisor.mir b/llvm/test/CodeGen/AMDGPU/dummy-regalloc-priority-advisor.mir
new file mode 100644
index 00000000000000..5c7c07632f0d59
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/dummy-regalloc-priority-advisor.mir
@@ -0,0 +1,54 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -start-before=greedy,2 -stress-regalloc=4 -stop-after=virtregrewriter,2 -regalloc-enable-priority-advisor=default -o - %s | FileCheck -check-prefixes=CHECK,DEFAULT %s
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -start-before=greedy,2 -stress-regalloc=4 -stop-after=virtregrewriter,2 -regalloc-enable-priority-advisor=dummy -o - %s | FileCheck -check-prefixes=CHECK,DUMMY %s
+
+# Check that the regalloc-enable-priority-advisor=dummy option works
+# and the result is different from the default. Ordinarily %1 would be
+# prioritized higher than %0 due to the register class priority
+
+---
+name: foo
+tracksRegLiveness: true
+machineFunctionInfo:
+ scratchRSrcReg: '$sgpr0_sgpr1_sgpr2_sgpr3'
+ frameOffsetReg: '$sgpr33'
+ stackPtrOffsetReg: '$sgpr32'
+registers:
+ - { id: 0, class: vgpr_32 }
+ - { id: 1, class: vreg_128 }
+ - { id: 2, class: vgpr_32 }
+body: |
+ bb.0:
+ liveins: $vgpr0, $vgpr1
+
+ ; DEFAULT-LABEL: name: foo
+ ; DEFAULT: liveins: $vgpr0, $vgpr1
+ ; DEFAULT-NEXT: {{ $}}
+ ; DEFAULT-NEXT: SI_SPILL_V128_SAVE $vgpr1_vgpr2_vgpr3_vgpr4, %stack.0, $sgpr32, 0, implicit $exec :: (store (s128) into %stack.0, align 4, addrspace 5)
+ ; DEFAULT-NEXT: SI_SPILL_V32_SAVE $vgpr0, %stack.1, $sgpr32, 0, implicit $exec :: (store (s32) into %stack.1, addrspace 5)
+ ; DEFAULT-NEXT: S_NOP 0, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3
+ ; DEFAULT-NEXT: renamable $vgpr2_vgpr3_vgpr4_vgpr5 = SI_SPILL_V128_RESTORE %stack.0, $sgpr32, 0, implicit $exec :: (load (s128) from %stack.0, align 4, addrspace 5)
+ ; DEFAULT-NEXT: renamable $vgpr3 = SI_SPILL_V32_RESTORE %stack.1, $sgpr32, 0, implicit $exec :: (load (s32) from %stack.1, addrspace 5)
+ ; DEFAULT-NEXT: renamable $vgpr3 = V_ADD_U32_e32 killed $vgpr2, killed $vgpr3, implicit $exec
+ ; DEFAULT-NEXT: SI_RETURN implicit $vgpr3, implicit $vgpr0, implicit $vgpr1
+ ;
+ ; DUMMY-LABEL: name: foo
+ ; DUMMY: liveins: $vgpr0, $vgpr1
+ ; DUMMY-NEXT: {{ $}}
+ ; DUMMY-NEXT: SI_SPILL_V128_SAVE $vgpr1_vgpr2_vgpr3_vgpr4, %stack.1, $sgpr32, 0, implicit $exec :: (store (s128) into %stack.1, align 4, addrspace 5)
+ ; DUMMY-NEXT: SI_SPILL_V32_SAVE $vgpr0, %stack.0, $sgpr32, 0, implicit $exec :: (store (s32) into %stack.0, addrspace 5)
+ ; DUMMY-NEXT: S_NOP 0, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3
+ ; DUMMY-NEXT: renamable $vgpr2 = SI_SPILL_V32_RESTORE %stack.0, $sgpr32, 0, implicit $exec :: (load (s32) from %stack.0, addrspace 5)
+ ; DUMMY-NEXT: renamable $vgpr3_vgpr4_vgpr5_vgpr6 = SI_SPILL_V128_RESTORE %stack.1, $sgpr32, 0, implicit $exec :: (load (s128) from %stack.1, align 4, addrspace 5)
+ ; DUMMY-NEXT: renamable $vgpr3 = V_ADD_U32_e32 killed $vgpr3, killed $vgpr2, implicit $exec
+ ; DUMMY-NEXT: SI_RETURN implicit $vgpr3, implicit $vgpr0, implicit $vgpr1
+ undef %1.sub0:vreg_128 = COPY $vgpr1
+ %0:vgpr_32 = COPY $vgpr0
+ S_NOP 0, implicit-def $vgpr0_vgpr1_vgpr2_vgpr3
+ %2:vgpr_32 = V_ADD_U32_e32 %1.sub0, %0, implicit $exec
+ $vgpr3 = COPY %2
+ SI_RETURN implicit $vgpr3, implicit $vgpr0, implicit $vgpr1
+
+...
+
+# CHECK: {{.*}}
``````````
</details>
https://github.com/llvm/llvm-project/pull/121207
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