From 8b13b11f11ccb540831999a24701d2c4bd8dfe1c Mon Sep 17 00:00:00 2001 From: =?utf8?q?Nicolai=20H=C3=A4hnle?= Date: Fri, 31 Mar 2017 18:42:51 +0200 Subject: [PATCH] radeonsi: optimization barriers to work around LLVM deficiencies MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Notably, llvm.amdgcn.readfirstlane and llvm.amdgcn.icmp may be hoisted out of loops or if/else branches in cases like if (cond) { v = readFirstInvocationARB(x); ... use v ... } else { v = readFirstInvocationARB(x); ... use v ... } ===> v = readFirstInvocationARB(x); if (cond) { ... use v ... } else { ... use v ... } The optimization barrier is a heavy hammer to stop that until LLVM is taught the semantics of the intrinsic properly. Reviewed-by: Marek Olšák --- src/gallium/drivers/radeonsi/si_shader.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c index 082e29111bd..3622acb3181 100644 --- a/src/gallium/drivers/radeonsi/si_shader.c +++ b/src/gallium/drivers/radeonsi/si_shader.c @@ -3131,7 +3131,6 @@ static void build_tex_intrinsic(const struct lp_build_tgsi_action *action, * Optionally, a value can be passed through the inline assembly to prevent * LLVM from hoisting calls to ReadNone functions. */ -#if 0 /* unused currently */ static void emit_optimization_barrier(struct si_shader_context *ctx, LLVMValueRef *pvgpr) { @@ -3165,7 +3164,6 @@ static void emit_optimization_barrier(struct si_shader_context *ctx, *pvgpr = vgpr; } } -#endif /* Combine these with & instead of |. */ #define NOOP_WAITCNT 0xf7f @@ -5176,8 +5174,13 @@ static LLVMValueRef si_emit_ballot(struct si_shader_context *ctx, LLVMConstInt(ctx->i32, LLVMIntNE, 0) }; - if (LLVMTypeOf(value) != ctx->i32) - args[0] = LLVMBuildBitCast(gallivm->builder, value, ctx->i32, ""); + /* We currently have no other way to prevent LLVM from lifting the icmp + * calls to a dominating basic block. + */ + emit_optimization_barrier(ctx, &args[0]); + + if (LLVMTypeOf(args[0]) != ctx->i32) + args[0] = LLVMBuildBitCast(gallivm->builder, args[0], ctx->i32, ""); return lp_build_intrinsic(gallivm->builder, "llvm.amdgcn.icmp.i32", @@ -5282,6 +5285,11 @@ static void read_lane_emit( struct si_shader_context *ctx = si_shader_context(bld_base); LLVMBuilderRef builder = ctx->gallivm.builder; + /* We currently have no other way to prevent LLVM from lifting the icmp + * calls to a dominating basic block. + */ + emit_optimization_barrier(ctx, &emit_data->args[0]); + for (unsigned i = 0; i < emit_data->arg_count; ++i) { emit_data->args[i] = LLVMBuildBitCast(builder, emit_data->args[i], ctx->i32, ""); -- 2.30.2