[AMDGPU] Add wave barrier builtin

The wave barrier represents the discardable barrier. Its main purpose is to
carry convergent attribute, thus preventing illegal CFG optimizations. All lanes
in a wave come to convergence point simultaneously with SIMT, thus no special
instruction is needed in the ISA. The barrier is discarded during code generation.

Differential Revision: https://reviews.llvm.org/D26585

llvm-svn: 287007

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp b/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
index cb259a38389..7d56355074b 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
@@ -196,6 +196,12 @@ void AMDGPUAsmPrinter::EmitInstruction(const MachineInstr *MI) {
       return;
     }
 
+    if (MI->getOpcode() == AMDGPU::WAVE_BARRIER) {
+      if (isVerbose())
+        OutStreamer->emitRawComment(" wave barrier");
+      return;
+    }
+
     MCInst TmpInst;
     MCInstLowering.lower(MI, TmpInst);
     EmitToStreamer(*OutStreamer, TmpInst);