Index: llvm/trunk/lib/Target/AMDGPU/SILowerControlFlow.cpp =================================================================== --- llvm/trunk/lib/Target/AMDGPU/SILowerControlFlow.cpp +++ llvm/trunk/lib/Target/AMDGPU/SILowerControlFlow.cpp @@ -137,6 +137,12 @@ NumInstr < SkipThreshold && I != E; ++I) { if (I->isBundle() || !I->isBundled()) + // When a uniform loop is inside non-uniform control flow, the branch + // leaving the loop might be an S_CBRANCH_VCCNZ, which is never taken + // when EXEC = 0. We should skip the loop lest it becomes infinite. + if (I->getOpcode() == AMDGPU::S_CBRANCH_VCCNZ) + return true; + if (++NumInstr >= SkipThreshold) return true; } Index: llvm/trunk/test/CodeGen/AMDGPU/uniform-loop-inside-nonuniform.ll =================================================================== --- llvm/trunk/test/CodeGen/AMDGPU/uniform-loop-inside-nonuniform.ll +++ llvm/trunk/test/CodeGen/AMDGPU/uniform-loop-inside-nonuniform.ll @@ -0,0 +1,28 @@ +;RUN: llc -march=amdgcn -mcpu=verde < %s | FileCheck %s --check-prefix=CHECK + +; Test a simple uniform loop that lives inside non-uniform control flow. + +;CHECK-LABEL: {{^}}test1: +;CHECK: s_cbranch_execz +;CHECK: %loop_body +define void @test1(<8 x i32> inreg %rsrc, <2 x i32> %addr.base, i32 %y, i32 %p) #0 { +main_body: + %cc = icmp eq i32 %p, 0 + br i1 %cc, label %out, label %loop_body + +loop_body: + %counter = phi i32 [ 0, %main_body ], [ %incr, %loop_body ] + + ; Prevent the loop from being optimized out + call void asm sideeffect "", "" () + + %incr = add i32 %counter, 1 + %lc = icmp sge i32 %incr, 1000 + br i1 %lc, label %out, label %loop_body + +out: + ret void +} + +attributes #0 = { "ShaderType"="0" } +attributes #1 = { nounwind readonly }