[clang] [llvm] [AMDGPU] Emit a waitcnt instruction after each memory instruction (PR #79236)

[Tony Tye via cfe-commits]

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@@ -605,12 +606,197 @@ class SIGfx12CacheControl : public SIGfx11CacheControl {
                                       bool IsNonTemporal) const override;
 };
 
+class SIPreciseMemorySupport {
+protected:
+  const GCNSubtarget &ST;
+  const SIInstrInfo *TII = nullptr;
+
+  IsaVersion IV;
+
+  SIPreciseMemorySupport(const GCNSubtarget &ST) : ST(ST) {
+    TII = ST.getInstrInfo();
+    IV = getIsaVersion(ST.getCPU());
+  }
+
+public:
+  static std::unique_ptr<SIPreciseMemorySupport> create(const GCNSubtarget &ST);
+
+  virtual bool handleNonAtomic(MachineBasicBlock::iterator &MI) = 0;
+  /// Handles atomic instruction \p MI with \p ret indicating whether \p MI
+  /// returns a result.
+  virtual bool handleAtomic(MachineBasicBlock::iterator &MI, bool ret) = 0;
+};
+
+class SIGfx9PreciseMemorySupport : public SIPreciseMemorySupport {
+public:
+  SIGfx9PreciseMemorySupport(const GCNSubtarget &ST)
+      : SIPreciseMemorySupport(ST) {}
+  bool handleNonAtomic(MachineBasicBlock::iterator &MI) override;
+  bool handleAtomic(MachineBasicBlock::iterator &MI, bool ret) override;
+};
+
+class SIGfx10And11PreciseMemorySupport : public SIPreciseMemorySupport {
+public:
+  SIGfx10And11PreciseMemorySupport(const GCNSubtarget &ST)
+      : SIPreciseMemorySupport(ST) {}
+  bool handleNonAtomic(MachineBasicBlock::iterator &MI) override;
+  bool handleAtomic(MachineBasicBlock::iterator &MI, bool ret) override;
+};
+
+std::unique_ptr<SIPreciseMemorySupport>
+SIPreciseMemorySupport::create(const GCNSubtarget &ST) {
+  GCNSubtarget::Generation Generation = ST.getGeneration();
+  if (Generation < AMDGPUSubtarget::GFX10)
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t-tye wrote:

Is there a reason that this functionality should not be available for any target? It is true it is only particularly useful for targets that have no precise memory operations hardware support, but the basic idea is meaningful for any target.

https://github.com/llvm/llvm-project/pull/79236