[llvm] r295539 - AMDGPU/R600: Assert on infinite loop in EmitClauseMarkers

[David Blaikie via llvm-commits]

This seems not quite right for a few reasons:

* If this code is reachable, an assertion isn't appropriate (assertions
should not be reachable - there are some tests for assertions failures in
unit tests, to demonstrate that those APIs assert fail on misuse, for
example) - maybe report_fatal_error is what's required here?

* XFAIL isn't the right tool for a test for failure - "not llc" or the like
(I'm not sure if lit supports that exact syntax, or it requires something
else) would probably be the right thing.

* This test would (if it remains in tree) need "REQUIRES: Asserts"
otherwise it introduces an infinite loop in non-asserts builds. (I'm not
sure why this isn't breaking any release building bot with the AMDGPU
backend enabled)

On Fri, Feb 17, 2017 at 8:35 PM Jan Vesely via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: jvesely
> Date: Fri Feb 17 22:24:10 2017
> New Revision: 295539
>
> URL: http://llvm.org/viewvc/llvm-project?rev=295539&view=rev
> Log:
> AMDGPU/R600: Assert on infinite loop in EmitClauseMarkers
>
> Differential Revision: https://reviews.llvm.org/D29792
>
> Added:
>     llvm/trunk/test/CodeGen/AMDGPU/r600.alu-limits.ll
> Modified:
>     llvm/trunk/lib/Target/AMDGPU/R600EmitClauseMarkers.cpp
>
> Modified: llvm/trunk/lib/Target/AMDGPU/R600EmitClauseMarkers.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AMDGPU/R600EmitClauseMarkers.cpp?rev=295539&r1=295538&r2=295539&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Target/AMDGPU/R600EmitClauseMarkers.cpp (original)
> +++ llvm/trunk/lib/Target/AMDGPU/R600EmitClauseMarkers.cpp Fri Feb 17
> 22:24:10 2017
> @@ -321,9 +321,11 @@ public:
>        if (I != MBB.end() && I->getOpcode() == AMDGPU::CF_ALU)
>          continue; // BB was already parsed
>        for (MachineBasicBlock::iterator E = MBB.end(); I != E;) {
> -        if (isALU(*I))
> -          I = MakeALUClause(MBB, I);
> -        else
> +        if (isALU(*I)) {
> +          auto next = MakeALUClause(MBB, I);
> +          assert(next != I);
> +          I = next;
> +        } else
>            ++I;
>        }
>      }
>
> Added: llvm/trunk/test/CodeGen/AMDGPU/r600.alu-limits.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AMDGPU/r600.alu-limits.ll?rev=295539&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/AMDGPU/r600.alu-limits.ll (added)
> +++ llvm/trunk/test/CodeGen/AMDGPU/r600.alu-limits.ll Fri Feb 17 22:24:10
> 2017
> @@ -0,0 +1,28 @@
> +; RUN: opt -loop-unroll -unroll-threshold=2000 -S < %s | llc -march=r600
> -mcpu=cypress | FileCheck %s
> +; XFAIL: *
> +
> +; CHECK: {{^}}@alu_limits:
> +
> +%struct.foo = type {i32, i32, i32}
> +
> +define void @alu_limits(i32 addrspace(1)* %out, %struct.foo* %in, i32
> %offset) {
> +entry:
> +  %ptr = getelementptr inbounds %struct.foo, %struct.foo* %in, i32 1, i32
> 2
> +  %x = load i32, i32 *%ptr, align 4
> +  br label %loop
> +loop:
> +  %i = phi i32 [ 100, %entry ], [ %nexti, %loop ]
> +  %val = phi i32 [ 1, %entry ], [ %nextval, %loop ]
> +
> +  %nexti = sub i32 %i, 1
> +
> +  %y = xor i32 %x, %i
> +  %nextval = mul i32 %val, %y
> +
> +  %cond = icmp ne i32 %nexti, 0
> +  br i1 %cond, label %loop, label %end
> +end:
> +  %out_val = add i32 %nextval, 4
> +  store i32 %out_val, i32 addrspace(1)* %out, align 4
> +  ret void
> +}
>
>
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