From: Nicolai Hähnle <nicolai.haeh...@amd.com>
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.
---
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 a56e886..a24db0d 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -3146,21 +3146,20 @@ static void build_tex_intrinsic(const struct
lp_build_tgsi_action *action,
struct lp_build_tgsi_context *bld_base,
struct lp_build_emit_data *emit_data);
/* Prevent optimizations (at least of memory accesses) across the current
* point in the program by emitting empty inline assembly that is marked as
* having side effects.
*
* 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)
{
static int counter = 0;
LLVMBuilderRef builder = ctx->gallivm.builder;
char code[16];
snprintf(code, sizeof(code), "; %d", p_atomic_inc_return(&counter));
@@ -3180,21 +3179,20 @@ static void emit_optimization_barrier(struct
si_shader_context *ctx,
vgpr = LLVMBuildBitCast(builder, vgpr, LLVMVectorType(ctx->i32,
vgpr_size / 4), "");
vgpr0 = LLVMBuildExtractElement(builder, vgpr, ctx->i32_0, "");
vgpr0 = LLVMBuildCall(builder, inlineasm, &vgpr0, 1, "");
vgpr = LLVMBuildInsertElement(builder, vgpr, vgpr0, ctx->i32_0,
"");
vgpr = LLVMBuildBitCast(builder, vgpr, vgpr_type, "");
*pvgpr = vgpr;
}
}
-#endif
/* Combine these with & instead of |. */
#define NOOP_WAITCNT 0xf7f
#define LGKM_CNT 0x07f
#define VM_CNT 0xf70
static void emit_waitcnt(struct si_shader_context *ctx, unsigned simm16)
{
struct gallivm_state *gallivm = &ctx->gallivm;
LLVMBuilderRef builder = gallivm->builder;
@@ -5201,22 +5199,27 @@ static void build_interp_intrinsic(const struct
lp_build_tgsi_action *action,
static LLVMValueRef si_emit_ballot(struct si_shader_context *ctx,
LLVMValueRef value)
{
struct gallivm_state *gallivm = &ctx->gallivm;
LLVMValueRef args[3] = {
value,
ctx->i32_0,
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",
ctx->i64, args, 3,
LP_FUNC_ATTR_NOUNWIND |
LP_FUNC_ATTR_READNONE |
LP_FUNC_ATTR_CONVERGENT);
}
static void vote_all_emit(
@@ -5307,20 +5310,25 @@ static void read_invoc_fetch_args(
}
static void read_lane_emit(
const struct lp_build_tgsi_action *action,
struct lp_build_tgsi_context *bld_base,
struct lp_build_emit_data *emit_data)
{
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, "");
}
emit_data->output[emit_data->chan] =
ac_build_intrinsic(&ctx->ac, action->intr_name,
ctx->i32, emit_data->args,
emit_data->arg_count,
AC_FUNC_ATTR_READNONE |
AC_FUNC_ATTR_CONVERGENT);
--
2.9.3
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