[PPCGCodeGeneration] Fix runtime check adjustments since they make assumptions about BB layout.

- There is a conditional branch that is used to switch between the old
   and new versions of the code.

- If we detect that the build was unsuccessful, `PPCGCodeGeneration` will
  change the runtime check to be always set to false.

- To actually *reach* this runtime check instruction, `PPCGCodeGeneration`
  was using assumptions about the layout of the BBs.

- However, invariant load hoisting violates this assumption by inserting
  an extra basic block in the middle.

- Fix the assumption on the layout by having `createScopConditionally`
   return the conditional branch instruction.

- Use this reference to set to always-false.

llvm-svn: 308010

1 files changed, 7 insertions, 3 deletions

diff --git a/polly/lib/CodeGen/PPCGCodeGeneration.cpp b/polly/lib/CodeGen/PPCGCodeGeneration.cpp
index 7b096a1917a2..6ccf78748cc7 100644
--- a/polly/lib/CodeGen/PPCGCodeGeneration.cpp
+++ b/polly/lib/CodeGen/PPCGCodeGeneration.cpp
@@ -2935,10 +2935,14 @@ public:
     // the SCEVExpander may introduce while code generating the parameters and
     // which may introduce scalar dependences that prevent us from correctly
     // code generating this scop.
-    BBPair StartExitBlocks =
+    BBPair StartExitBlocks;
+    BranchInst *CondBr = nullptr;
+    std::tie(StartExitBlocks, CondBr) =
         executeScopConditionally(*S, Builder.getTrue(), *DT, *RI, *LI);
     BasicBlock *StartBlock = std::get<0>(StartExitBlocks);
 
+    assert(CondBr && "CondBr not initialized by executeScopConditionally");
+
     GPUNodeBuilder NodeBuilder(Builder, Annotator, *DL, *LI, *SE, *DT, *S,
                                StartBlock, Prog, Runtime, Architecture);
 
@@ -2966,10 +2970,10 @@ public:
     /// kernel, the SCoP is probably mostly sequential. Hence, there is no
     /// point in running it on a GPU.
     if (NodeBuilder.DeepestSequential > NodeBuilder.DeepestParallel)
-      SplitBlock->getTerminator()->setOperand(0, Builder.getFalse());
+      CondBr->setOperand(0, Builder.getFalse());
 
     if (!NodeBuilder.BuildSuccessful)
-      SplitBlock->getTerminator()->setOperand(0, Builder.getFalse());
+      CondBr->setOperand(0, Builder.getFalse());
   }
 
   bool runOnScop(Scop &CurrentScop) override {