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@@ -47,6 +47,7 @@
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#include "source/opcode.h"
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#include "source/opt/cfg.h"
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#include "source/opt/mem_pass.h"
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+#include "source/opt/types.h"
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#include "source/util/make_unique.h"
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// Debug logging (0: Off, 1-N: Verbosity level). Replace this with the
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@@ -326,32 +327,94 @@ void SSARewriter::ProcessStore(Instruction* inst, BasicBlock* bb) {
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}
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bool SSARewriter::ProcessLoad(Instruction* inst, BasicBlock* bb) {
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+ // Get the pointer that we are using to load from.
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uint32_t var_id = 0;
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(void)pass_->GetPtr(inst, &var_id);
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- if (pass_->IsTargetVar(var_id)) {
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- // Get the immediate reaching definition for |var_id|.
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- uint32_t val_id = GetReachingDef(var_id, bb);
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+
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+ // Get the immediate reaching definition for |var_id|.
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+ //
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+ // In the presence of variable pointers, the reaching definition may be
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+ // another pointer. For example, the following fragment:
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+ //
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+ // %2 = OpVariable %_ptr_Input_float Input
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+ // %11 = OpVariable %_ptr_Function__ptr_Input_float Function
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+ // OpStore %11 %2
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+ // %12 = OpLoad %_ptr_Input_float %11
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+ // %13 = OpLoad %float %12
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+ //
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+ // corresponds to the pseudo-code:
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+ //
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+ // layout(location = 0) in flat float *%2
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+ // float %13;
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+ // float *%12;
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+ // float **%11;
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+ // *%11 = %2;
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+ // %12 = *%11;
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+ // %13 = *%12;
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+ //
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+ // which ultimately, should correspond to:
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+ //
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+ // %13 = *%2;
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+ //
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+ // During rewriting, the pointer %12 is found to be replaceable by %2 (i.e.,
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+ // load_replacement_[12] is 2). However, when processing the load
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+ // %13 = *%12, the type of %12's reaching definition is another float
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+ // pointer (%2), instead of a float value.
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+ //
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+ // When this happens, we need to continue looking up the reaching definition
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+ // chain until we get to a float value or a non-target var (i.e. a variable
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+ // that cannot be SSA replaced, like %2 in this case since it is a function
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+ // argument).
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+ analysis::DefUseManager* def_use_mgr = pass_->context()->get_def_use_mgr();
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+ analysis::TypeManager* type_mgr = pass_->context()->get_type_mgr();
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+ analysis::Type* load_type = type_mgr->GetType(inst->type_id());
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+ uint32_t val_id = 0;
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+ bool found_reaching_def = false;
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+ while (!found_reaching_def) {
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+ if (!pass_->IsTargetVar(var_id)) {
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+ // If the variable we are loading from is not an SSA target (globals,
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+ // function parameters), do nothing.
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+ return true;
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+ }
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+
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+ val_id = GetReachingDef(var_id, bb);
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if (val_id == 0) {
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return false;
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}
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- // Schedule a replacement for the result of this load instruction with
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- // |val_id|. After all the rewriting decisions are made, every use of
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- // this load will be replaced with |val_id|.
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- const uint32_t load_id = inst->result_id();
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- assert(load_replacement_.count(load_id) == 0);
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- load_replacement_[load_id] = val_id;
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- PhiCandidate* defining_phi = GetPhiCandidate(val_id);
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- if (defining_phi) {
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- defining_phi->AddUser(load_id);
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+ // If the reaching definition is a pointer type different than the type of
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+ // the instruction we are analyzing, then it must be a reference to another
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+ // pointer (otherwise, this would be invalid SPIRV). We continue
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+ // de-referencing it by making |val_id| be |var_id|.
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+ //
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+ // NOTE: if there is no reaching definition instruction, it means |val_id|
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+ // is an undef.
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+ Instruction* reaching_def_inst = def_use_mgr->GetDef(val_id);
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+ if (reaching_def_inst &&
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+ !type_mgr->GetType(reaching_def_inst->type_id())->IsSame(load_type)) {
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+ var_id = val_id;
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+ } else {
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+ found_reaching_def = true;
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}
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+ }
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+
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+ // Schedule a replacement for the result of this load instruction with
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+ // |val_id|. After all the rewriting decisions are made, every use of
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+ // this load will be replaced with |val_id|.
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+ uint32_t load_id = inst->result_id();
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+ assert(load_replacement_.count(load_id) == 0);
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+ load_replacement_[load_id] = val_id;
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+ PhiCandidate* defining_phi = GetPhiCandidate(val_id);
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+ if (defining_phi) {
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+ defining_phi->AddUser(load_id);
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+ }
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#if SSA_REWRITE_DEBUGGING_LEVEL > 1
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- std::cerr << "\tFound load: "
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- << inst->PrettyPrint(SPV_BINARY_TO_TEXT_OPTION_FRIENDLY_NAMES)
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- << " (replacement for %" << load_id << " is %" << val_id << ")\n";
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+ std::cerr << "\tFound load: "
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+ << inst->PrettyPrint(SPV_BINARY_TO_TEXT_OPTION_FRIENDLY_NAMES)
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+ << " (replacement for %" << load_id << " is %" << val_id << ")\n";
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#endif
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- }
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+
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return true;
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}
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@@ -390,8 +453,8 @@ bool SSARewriter::GenerateSSAReplacements(BasicBlock* bb) {
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}
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}
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- // Seal |bb|. This means that all the stores in it have been scanned and it's
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- // ready to feed them into its successors.
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+ // Seal |bb|. This means that all the stores in it have been scanned and
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+ // it's ready to feed them into its successors.
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SealBlock(bb);
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#if SSA_REWRITE_DEBUGGING_LEVEL > 1
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@@ -504,8 +567,8 @@ bool SSARewriter::ApplyReplacements() {
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}
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// Scan uses for all inserted Phi instructions. Do this separately from the
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- // registration of the Phi instruction itself to avoid trying to analyze uses
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- // of Phi instructions that have not been registered yet.
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+ // registration of the Phi instruction itself to avoid trying to analyze
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+ // uses of Phi instructions that have not been registered yet.
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for (Instruction* phi_inst : generated_phis) {
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pass_->get_def_use_mgr()->AnalyzeInstUse(&*phi_inst);
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}
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@@ -562,7 +625,8 @@ void SSARewriter::FinalizePhiCandidate(PhiCandidate* phi_candidate) {
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// This candidate is now completed.
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phi_candidate->MarkComplete();
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- // If |phi_candidate| is not trivial, add it to the list of Phis to generate.
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+ // If |phi_candidate| is not trivial, add it to the list of Phis to
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+ // generate.
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if (TryRemoveTrivialPhi(phi_candidate) == phi_candidate->result_id()) {
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// If we could not remove |phi_candidate|, it means that it is complete
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// and not trivial. Add it to the list of Phis to generate.
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Бранимир Караџић