[PATCH] R600/SI: Fix assertion on infinite loops.

[Tom Stellard]

On Mon, Feb 03, 2014 at 05:30:04PM -0800, Matt Arsenault wrote:
> This isn't the most useful case to fix in the real world, but bugpoint runs into this.

LGTM.

> 
> http://llvm-reviews.chandlerc.com/D2682
> 
> Files:
>   lib/Target/R600/SILowerControlFlow.cpp
>   test/CodeGen/R600/infinite-loop.ll
> 
> Index: lib/Target/R600/SILowerControlFlow.cpp
> ===================================================================
> --- lib/Target/R600/SILowerControlFlow.cpp
> +++ lib/Target/R600/SILowerControlFlow.cpp
> @@ -283,8 +283,10 @@
>  }
>  
>  void SILowerControlFlowPass::Branch(MachineInstr &MI) {
> -  assert(MI.getOperand(0).getMBB() == MI.getParent()->getNextNode());
> -  MI.eraseFromParent();
> +  if (MI.getOperand(0).getMBB() == MI.getParent()->getNextNode())
> +    MI.eraseFromParent();
> +
> +  // If these aren't equal, this is probably an infinite loop.
>  }
>  
>  void SILowerControlFlowPass::Kill(MachineInstr &MI) {
> Index: test/CodeGen/R600/infinite-loop.ll
> ===================================================================
> --- /dev/null
> +++ test/CodeGen/R600/infinite-loop.ll
> @@ -0,0 +1,17 @@
> +; RUN: llc -march=r600 -mcpu=SI -verify-machineinstrs < %s | FileCheck -check-prefix=SI %s
> +
> +; SI-LABEL: @infinite_loop:
> +; SI: V_MOV_B32_e32 [[REG:v[0-9]+]], 999
> +; SI: BB0_1:
> +; SI: BUFFER_STORE_DWORD [[REG]]
> +; SI: S_WAITCNT vmcnt(0) expcnt(0)
> +; SI: S_BRANCH BB0_1
> +define void @infinite_loop(i32 addrspace(1)* %out) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %entry, %for.body
> +  store i32 999, i32 addrspace(1)* %out, align 4
> +  br label %for.body
> +}
> +

> Index: lib/Target/R600/SILowerControlFlow.cpp
> ===================================================================
> --- lib/Target/R600/SILowerControlFlow.cpp
> +++ lib/Target/R600/SILowerControlFlow.cpp
> @@ -283,8 +283,10 @@
>  }
>  
>  void SILowerControlFlowPass::Branch(MachineInstr &MI) {
> -  assert(MI.getOperand(0).getMBB() == MI.getParent()->getNextNode());
> -  MI.eraseFromParent();
> +  if (MI.getOperand(0).getMBB() == MI.getParent()->getNextNode())
> +    MI.eraseFromParent();
> +
> +  // If these aren't equal, this is probably an infinite loop.
>  }
>  
>  void SILowerControlFlowPass::Kill(MachineInstr &MI) {
> Index: test/CodeGen/R600/infinite-loop.ll
> ===================================================================
> --- /dev/null
> +++ test/CodeGen/R600/infinite-loop.ll
> @@ -0,0 +1,17 @@
> +; RUN: llc -march=r600 -mcpu=SI -verify-machineinstrs < %s | FileCheck -check-prefix=SI %s
> +
> +; SI-LABEL: @infinite_loop:
> +; SI: V_MOV_B32_e32 [[REG:v[0-9]+]], 999
> +; SI: BB0_1:
> +; SI: BUFFER_STORE_DWORD [[REG]]
> +; SI: S_WAITCNT vmcnt(0) expcnt(0)
> +; SI: S_BRANCH BB0_1
> +define void @infinite_loop(i32 addrspace(1)* %out) {
> +entry:
> +  br label %for.body
> +
> +for.body:                                         ; preds = %entry, %for.body
> +  store i32 999, i32 addrspace(1)* %out, align 4
> +  br label %for.body
> +}
> +

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