[Lldb-commits] [PATCH] R600: Workaround for cayman loop bug

[Vincent Lejeune]

Some shadertoy's sample were setting cayman gpus in a lock up state because of a hw bug
(CF_ALU_PUSH_BEFORE stack might be corrupted inside a nested loop, so we expand these instructions to PUSH;CF_ALU)

http://llvm-reviews.chandlerc.com/D2192

Files:
  lib/Target/R600/R600ControlFlowFinalizer.cpp
  lib/Target/R600/R600Instructions.td

Index: lib/Target/R600/R600ControlFlowFinalizer.cpp
===================================================================
--- lib/Target/R600/R600ControlFlowFinalizer.cpp
+++ lib/Target/R600/R600ControlFlowFinalizer.cpp
@@ -332,6 +332,7 @@
 
     unsigned MaxStack = 0;
     unsigned CurrentStack = 0;
+    unsigned CurrentLoopDepth = 0;
     bool HasPush = false;
     for (MachineFunction::iterator MB = MF.begin(), ME = MF.end(); MB != ME;
         ++MB) {
@@ -370,14 +371,22 @@
           CurrentStack++;
           MaxStack = std::max(MaxStack, CurrentStack);
           HasPush = true;
+          if (ST.hasCaymanISA() && CurrentLoopDepth > 1) {
+            BuildMI(MBB, MI, MBB.findDebugLoc(MI), TII->get(AMDGPU::CF_PUSH_CM))
+                .addImm(CfCount + 1)
+                .addImm(1);
+            MI->setDesc(TII->get(AMDGPU::CF_ALU));
+            CfCount++;
+          }
         case AMDGPU::CF_ALU:
           I = MI;
           AluClauses.push_back(MakeALUClause(MBB, I));
           DEBUG(dbgs() << CfCount << ":"; MI->dump(););
           CfCount++;
           break;
         case AMDGPU::WHILELOOP: {
           CurrentStack+=4;
+          CurrentLoopDepth ++;
           MaxStack = std::max(MaxStack, CurrentStack);
           MachineInstr *MIb = BuildMI(MBB, MI, MBB.findDebugLoc(MI),
               getHWInstrDesc(CF_WHILE_LOOP))
@@ -392,6 +401,7 @@
         }
         case AMDGPU::ENDLOOP: {
           CurrentStack-=4;
+          CurrentLoopDepth --;
           std::pair<unsigned, std::set<MachineInstr *> > Pair =
               LoopStack.back();
           LoopStack.pop_back();
Index: lib/Target/R600/R600Instructions.td
===================================================================
--- lib/Target/R600/R600Instructions.td
+++ lib/Target/R600/R600Instructions.td
@@ -1854,6 +1854,10 @@
     let COUNT = 0;
   }
 
+  def CF_PUSH_CM : CF_CLAUSE_EG<11, (ins i32imm:$ADDR, i32imm:$POP_COUNT), "PUSH @$ADDR POP:$POP_COUNT"> {
+    let COUNT = 0;
+  }
+
 def : Pat<(fsqrt f32:$src), (MUL R600_Reg32:$src, (RECIPSQRT_CLAMPED_cm $src))>;
 
 class RAT_STORE_DWORD <RegisterClass rc, ValueType vt, bits<4> mask> :
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