[PATCH] D19709: AMDGPU: Fix crash with unreachable terminators.

[Matt Arsenault via llvm-commits]

arsenm created this revision.
arsenm added reviewers: tstellarAMD, nhaehnle.
arsenm added a subscriber: llvm-commits.
Herald added a subscriber: arsenm.

If a block has no successors because it ends in unreachable,
this was accessing an invalid iterator.
    
Also stop counting instructions that don't emit any
real instructions.

http://reviews.llvm.org/D19709

Files:
  lib/Target/AMDGPU/SILowerControlFlow.cpp

Index: lib/Target/AMDGPU/SILowerControlFlow.cpp
===================================================================
--- lib/Target/AMDGPU/SILowerControlFlow.cpp
+++ lib/Target/AMDGPU/SILowerControlFlow.cpp
@@ -125,29 +125,44 @@
   return new SILowerControlFlow();
 }
 
+static bool opcodeEmitsNoInsts(unsigned Opc) {
+  switch (Opc) {
+  case TargetOpcode::IMPLICIT_DEF:
+  case TargetOpcode::KILL:
+  case TargetOpcode::BUNDLE:
+  case TargetOpcode::CFI_INSTRUCTION:
+  case TargetOpcode::EH_LABEL:
+  case TargetOpcode::GC_LABEL:
+  case TargetOpcode::DBG_VALUE:
+    return true;
+  default:
+    return false;
+  }
+}
+
 bool SILowerControlFlow::shouldSkip(MachineBasicBlock *From,
                                     MachineBasicBlock *To) {
 
   unsigned NumInstr = 0;
+  MachineFunction *MF = From->getParent();
 
-  for (MachineFunction::iterator MBBI = MachineFunction::iterator(From),
-                                 ToI = MachineFunction::iterator(To); MBBI != ToI; ++MBBI) {
-
+  for (MachineFunction::iterator MBBI(From), ToI(To), End = MF->end();
+       MBBI != End && MBBI != ToI; ++MBBI) {
     MachineBasicBlock &MBB = *MBBI;
 
     for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
          NumInstr < SkipThreshold && I != E; ++I) {
+      if (opcodeEmitsNoInsts(I->getOpcode()))
+        continue;
 
-      if (I->isBundle() || !I->isBundled()) {
-        // When a uniform loop is inside non-uniform control flow, the branch
-        // leaving the loop might be an S_CBRANCH_VCCNZ, which is never taken
-        // when EXEC = 0. We should skip the loop lest it becomes infinite.
-        if (I->getOpcode() == AMDGPU::S_CBRANCH_VCCNZ)
-          return true;
+      // When a uniform loop is inside non-uniform control flow, the branch
+      // leaving the loop might be an S_CBRANCH_VCCNZ, which is never taken
+      // when EXEC = 0. We should skip the loop lest it becomes infinite.
+      if (I->getOpcode() == AMDGPU::S_CBRANCH_VCCNZ)
+        return true;
 
-        if (++NumInstr >= SkipThreshold)
-          return true;
-      }
+      if (++NumInstr >= SkipThreshold)
+        return true;
     }
   }
 


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