From ca05a13c62ad7693f8be924c168e400e8139b0d2 Mon Sep 17 00:00:00 2001
From: ReinUsesLisp <reinuseslisp@airmail.cc>
Date: Tue, 25 May 2021 02:22:21 -0300
Subject: glasm: Catch more register leaks

Add support for null registers. These are used when an instruction has
no usages.

This comes handy when an instruction is only used for its CC value, with
the caveat of having to invalidate all pseudo-instructions before
defining the instruction itself in the register allocator. This commits
changes this.

Workaround a bug on Nvidia's condition codes conditional execution using
branches.
---
 .../backend/glasm/emit_glasm_integer.cpp           | 58 +++++++++++++++-------
 1 file changed, 40 insertions(+), 18 deletions(-)

(limited to 'src/shader_recompiler/backend/glasm/emit_glasm_integer.cpp')

diff --git a/src/shader_recompiler/backend/glasm/emit_glasm_integer.cpp b/src/shader_recompiler/backend/glasm/emit_glasm_integer.cpp
index e5aac14c8..e9d1bae05 100644
--- a/src/shader_recompiler/backend/glasm/emit_glasm_integer.cpp
+++ b/src/shader_recompiler/backend/glasm/emit_glasm_integer.cpp
@@ -9,6 +9,17 @@
 namespace Shader::Backend::GLASM {
 
 void EmitIAdd32(EmitContext& ctx, IR::Inst& inst, ScalarS32 a, ScalarS32 b) {
+    const std::array flags{
+        inst.GetAssociatedPseudoOperation(IR::Opcode::GetZeroFromOp),
+        inst.GetAssociatedPseudoOperation(IR::Opcode::GetSignFromOp),
+        inst.GetAssociatedPseudoOperation(IR::Opcode::GetCarryFromOp),
+        inst.GetAssociatedPseudoOperation(IR::Opcode::GetOverflowFromOp),
+    };
+    for (IR::Inst* const flag_inst : flags) {
+        if (flag_inst) {
+            flag_inst->Invalidate();
+        }
+    }
     const bool cc{inst.HasAssociatedPseudoOperation()};
     const std::string_view cc_mod{cc ? ".CC" : ""};
     if (cc) {
@@ -19,20 +30,22 @@ void EmitIAdd32(EmitContext& ctx, IR::Inst& inst, ScalarS32 a, ScalarS32 b) {
     if (!cc) {
         return;
     }
-    static constexpr std::array<std::string_view, 4> masks{"EQ", "SF", "CF", "OF"};
-    const std::array flags{
-        inst.GetAssociatedPseudoOperation(IR::Opcode::GetZeroFromOp),
-        inst.GetAssociatedPseudoOperation(IR::Opcode::GetSignFromOp),
-        inst.GetAssociatedPseudoOperation(IR::Opcode::GetCarryFromOp),
-        inst.GetAssociatedPseudoOperation(IR::Opcode::GetOverflowFromOp),
-    };
-    for (size_t i = 0; i < flags.size(); ++i) {
-        if (flags[i]) {
-            const auto flag_ret{ctx.reg_alloc.Define(*flags[i])};
-            ctx.Add("MOV.S {},0;"
-                    "MOV.S {}({}.x),-1;",
-                    flag_ret, flag_ret, masks[i]);
-            flags[i]->Invalidate();
+    static constexpr std::array<std::string_view, 4> masks{"", "SF", "CF", "OF"};
+    for (size_t flag_index = 0; flag_index < flags.size(); ++flag_index) {
+        if (!flags[flag_index]) {
+            continue;
+        }
+        const auto flag_ret{ctx.reg_alloc.Define(*flags[flag_index])};
+        if (flag_index == 0) {
+            ctx.Add("SEQ.S {}.x,{}.x,0;", flag_ret, ret);
+        } else {
+            // We could use conditional execution here, but it's broken on Nvidia's compiler
+            ctx.Add("IF {}.x;"
+                    "MOV.S {}.x,-1;"
+                    "ELSE;"
+                    "MOV.S {}.x,0;"
+                    "ENDIF;",
+                    masks[flag_index], flag_ret, flag_ret);
         }
     }
 }
@@ -136,6 +149,17 @@ void EmitBitFieldSExtract(EmitContext& ctx, IR::Inst& inst, ScalarS32 base, Scal
 
 void EmitBitFieldUExtract(EmitContext& ctx, IR::Inst& inst, ScalarU32 base, ScalarU32 offset,
                           ScalarU32 count) {
+    const auto zero = inst.GetAssociatedPseudoOperation(IR::Opcode::GetZeroFromOp);
+    const auto sign = inst.GetAssociatedPseudoOperation(IR::Opcode::GetSignFromOp);
+    if (zero) {
+        zero->Invalidate();
+    }
+    if (sign) {
+        sign->Invalidate();
+    }
+    if (zero || sign) {
+        ctx.reg_alloc.InvalidateConditionCodes();
+    }
     const Register ret{ctx.reg_alloc.Define(inst)};
     if (count.type != Type::Register && offset.type != Type::Register) {
         ctx.Add("BFE.U {},{{{},{},0,0}},{};", ret, count, offset, base);
@@ -145,13 +169,11 @@ void EmitBitFieldUExtract(EmitContext& ctx, IR::Inst& inst, ScalarU32 base, Scal
                 "BFE.U {},RC,{};",
                 count, offset, ret, base);
     }
-    if (const auto zero = inst.GetAssociatedPseudoOperation(IR::Opcode::GetZeroFromOp)) {
+    if (zero) {
         ctx.Add("SEQ.S {},{},0;", *zero, ret);
-        zero->Invalidate();
     }
-    if (const auto sign = inst.GetAssociatedPseudoOperation(IR::Opcode::GetSignFromOp)) {
+    if (sign) {
         ctx.Add("SLT.S {},{},0;", *sign, ret);
-        sign->Invalidate();
     }
 }
 
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