Fix the assert in Annotate the loop in SIAnnotateControlFlow pass when the loop terminator condition is a constant.

[cfang]

Summary

If the condition is a constant, we insert a IfBreak intrinsic immediately before the Terminator.
This will fix the assert.

[arsenm]

The test is missing check lines, so FileCheck will error on it

test/CodeGen/AMDGPU/si-annotate-cfg-loop-assert.ll

1–2

Isn't this fixing the test? Why is this xfailed?

6–7

These should be removed

11

Remove the align 2

15

Can you run opt -strip -instnamer on this test?

[cfang]

Updated based on Matt's comments.

[cfang]

indeed update the LIT test based on Matt's comment.

[• tstellarAMD]

lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

276–278

Usually getting a branch on constant in the SIAnnotateControlFlow means that there is a bug in the StructurizeCFG pass.
There is no harm in handling this here, but I think it may just be covering over a bug in the structurizer pass.

[cfang]

lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

276–278

Why do you think there is a bug in the structurizer? My understanding is that, for an infinite loop or a one-trip (do-while) loop, the condition can be a constant, even though we may be able to optimize away the loop for the later case.

[cfang]

Add CHECKS

[• tstellarAMD]

lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

276–278

This kind of failure is a common symptom of strurcturizer bugs. You should run llc with -print-before-all to see if the constant branch exists before the structurizer is run.

[cfang]

Any further comment?

lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

276–278

It is true that the structrizer has a bug generating wrong constant condition. However, in a general sense, nothing prevents
the condition from being constant. And as a result, we should handle constant condition in annotating loops.

[arsenm]

LGTM

lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

 
   void insertElse(BranchInst *Term);
 
-  Value *handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L);
+  Value *handleLoopCondition(Value *Cond, PHINode *Broken,
+                             llvm::Loop *L, BranchInst *Term);
 
   void handleLoop(BranchInst *Term);
 

 
 /// \brief Recursively handle the condition leading to a loop
 Value *SIAnnotateControlFlow::handleLoopCondition(Value *Cond, PHINode *Broken,
-                                                  llvm::Loop *L) {
+                                             llvm::Loop *L, BranchInst *Term) {
 
   // Only search through PHI nodes which are inside the loop.  If we try this
   // with PHI nodes that are outside of the loop, we end up inserting new PHI

       }
 
       Phi->setIncomingValue(i, BoolFalse);
-      Value *PhiArg = handleLoopCondition(Incoming, Broken, L);
+      Value *PhiArg = handleLoopCondition(Incoming, Broken, L, Term);
       NewPhi->addIncoming(PhiArg, From);
     }
 

     Value *Args[] = { Cond, Broken };
     return CallInst::Create(IfBreak, Args, "", Insert);
 
+  // Insert IfBreak before TERM for constant COND.
+  } else if (isa<ConstantInt>(Cond)) {
+    Value *Args[] = { Cond, Broken };
+    return CallInst::Create(IfBreak, Args, "", Term);
+
   } else {
     llvm_unreachable("Unhandled loop condition!");
   }

 
   Value *Cond = Term->getCondition();
   Term->setCondition(BoolTrue);
-  Value *Arg = handleLoopCondition(Cond, Broken, L);
+  Value *Arg = handleLoopCondition(Cond, Broken, L, Term);
 
   for (pred_iterator PI = pred_begin(Target), PE = pred_end(Target);
        PI != PE; ++PI) {

test/CodeGen/AMDGPU/si-annotate-cfg-loop-assert.ll

+; REQUIRES: asserts
+; XFAIL: *
+; RUN: llc -march=amdgcn -mcpu=kaveri  < %s | FileCheck %s
+
+
+target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
+target triple = "spir64-unknown-unknown"
+
+
+; Function Attrs: norecurse nounwind uwtable
+define spir_kernel void @test(i32, i32, i32 addrspace(1)* nocapture, i32, i32, i32, i32) #0 align 2 {
+  %8 = icmp ne i32 %0, 0
+  %9 = icmp ne i32 %1, 0
+  %or.cond.i.i = and i1 %8, %9
+  br i1 %or.cond.i.i, label %.lr.ph.i.i.preheader, label %"_ZZ9test_mainvENK3$_0clEN6Kalmar5indexILi2EEE.exit"
+
+.lr.ph.i.i.preheader:                             ; preds = %7
+  br label %.lr.ph.i.i
+
+.lr.ph.i.i:                                       ; preds = %.lr.ph.i.i.preheader, %.lr.ph.i.i
+  br label %.lr.ph.i.i
+
+"_ZZ9test_mainvENK3$_0clEN6Kalmar5indexILi2EEE.exit": ; preds = %7
+  ret void
+}
+