AMDGPU: Fix copying i1 value out of loop with non-uniform exit

Summary:
When an i1-value is defined inside of a loop and used outside of it, we
cannot simply use the SGPR bitmask from the loop's last iteration.

There are also useful and correct cases of an i1-value being copied between
basic blocks, e.g. when a condition is computed outside of a loop and used
inside it. The concept of dominators is not sufficient to capture what is
going on, so I propose the notion of "lane-dominators".

Fixes a bug encountered in Nier: Automata.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103743
Change-Id: If37b969ddc71d823ab3004aeafb9ea050e45bd9a

Reviewers: arsenm, rampitec

Subscribers: kzhuravl, wdng, mgorny, yaxunl, dstuttard, tpr, llvm-commits, t-tye

Differential Revision: https://reviews.llvm.org/D40547

llvm-svn: 329164

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/Utils/AMDGPULaneDominator.h b/llvm/lib/Target/AMDGPU/Utils/AMDGPULaneDominator.h
new file mode 100644
index 00000000000..4f33a89a364
--- /dev/null
+++ b/llvm/lib/Target/AMDGPU/Utils/AMDGPULaneDominator.h
@@ -0,0 +1,24 @@
+//===- AMDGPULaneDominator.h ------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_TARGET_AMDGPU_UTILS_AMDGPULANEDOMINATOR_H
+#define LLVM_LIB_TARGET_AMDGPU_UTILS_AMDGPULANEDOMINATOR_H
+
+namespace llvm {
+
+class MachineBasicBlock;
+
+namespace AMDGPU {
+
+bool laneDominates(MachineBasicBlock *MBBA, MachineBasicBlock *MBBB);
+
+} // end namespace AMDGPU
+} // end namespace llvm
+
+#endif // LLVM_LIB_TARGET_AMDGPU_UTILS_AMDGPULANEDOMINATOR_H