From 05d41fa9b70af6d469f2f6f1474436c9255e9bc3 Mon Sep 17 00:00:00 2001
From: ReinUsesLisp <reinuseslisp@airmail.cc>
Date: Sun, 30 May 2021 23:08:17 -0300
Subject: shader: Add support for "negative" and unaligned offsets

"Negative" offsets don't exist. They are shown as such due to a bug in
nvdisasm.

Unaligned offsets have been proved to read the aligned offset. For
example, when reading an U32, if the offset is 6, the offset read will
be 4.
---
 .../backend/glasm/emit_glasm_context_get_set.cpp                 | 8 ++++++++
 .../backend/spirv/emit_spirv_context_get_set.cpp                 | 9 +++------
 src/shader_recompiler/frontend/maxwell/translate/impl/impl.cpp   | 4 ++--
 3 files changed, 13 insertions(+), 8 deletions(-)

(limited to 'src')

diff --git a/src/shader_recompiler/backend/glasm/emit_glasm_context_get_set.cpp b/src/shader_recompiler/backend/glasm/emit_glasm_context_get_set.cpp
index 787612def..9ad668b86 100644
--- a/src/shader_recompiler/backend/glasm/emit_glasm_context_get_set.cpp
+++ b/src/shader_recompiler/backend/glasm/emit_glasm_context_get_set.cpp
@@ -18,6 +18,14 @@ void GetCbuf(EmitContext& ctx, IR::Inst& inst, const IR::Value& binding, ScalarU
         throw NotImplementedException("Indirect constant buffer loading");
     }
     const Register ret{ctx.reg_alloc.Define(inst)};
+    if (offset.type == Type::U32) {
+        // Avoid reading arrays out of bounds, matching hardware's behavior
+        const u32 imm_offset{offset.imm_u32};
+        if (offset.imm_u32 >= 0x10'000) {
+            ctx.Add("MOV.S {},0;", ret);
+            return;
+        }
+    }
     ctx.Add("LDC.{} {},c{}[{}];", size, ret, binding.U32(), offset);
 }
 
diff --git a/src/shader_recompiler/backend/spirv/emit_spirv_context_get_set.cpp b/src/shader_recompiler/backend/spirv/emit_spirv_context_get_set.cpp
index c1b69c234..442a958a5 100644
--- a/src/shader_recompiler/backend/spirv/emit_spirv_context_get_set.cpp
+++ b/src/shader_recompiler/backend/spirv/emit_spirv_context_get_set.cpp
@@ -122,7 +122,7 @@ std::optional<OutAttr> OutputAttrPointer(EmitContext& ctx, IR::Attribute attr) {
 }
 
 Id GetCbuf(EmitContext& ctx, Id result_type, Id UniformDefinitions::*member_ptr, u32 element_size,
-           const IR::Value& binding, const IR::Value& offset, bool check_alignment = true) {
+           const IR::Value& binding, const IR::Value& offset) {
     if (!binding.IsImmediate()) {
         throw NotImplementedException("Constant buffer indexing");
     }
@@ -138,17 +138,14 @@ Id GetCbuf(EmitContext& ctx, Id result_type, Id UniformDefinitions::*member_ptr,
         const Id access_chain{ctx.OpAccessChain(uniform_type, cbuf, ctx.u32_zero_value, index)};
         return ctx.OpLoad(result_type, access_chain);
     }
-    if (check_alignment && offset.U32() % element_size != 0) {
-        throw NotImplementedException("Unaligned immediate constant buffer load");
-    }
+    // Hardware been proved to read the aligned offset (e.g. LDC.U32 at 6 will read offset 4)
     const Id imm_offset{ctx.Const(offset.U32() / element_size)};
     const Id access_chain{ctx.OpAccessChain(uniform_type, cbuf, ctx.u32_zero_value, imm_offset)};
     return ctx.OpLoad(result_type, access_chain);
 }
 
 Id GetCbufU32x4(EmitContext& ctx, const IR::Value& binding, const IR::Value& offset) {
-    return GetCbuf(ctx, ctx.U32[4], &UniformDefinitions::U32x4, sizeof(u32[4]), binding, offset,
-                   false);
+    return GetCbuf(ctx, ctx.U32[4], &UniformDefinitions::U32x4, sizeof(u32[4]), binding, offset);
 }
 
 Id GetCbufElement(EmitContext& ctx, Id vector, const IR::Value& offset, u32 index_offset) {
diff --git a/src/shader_recompiler/frontend/maxwell/translate/impl/impl.cpp b/src/shader_recompiler/frontend/maxwell/translate/impl/impl.cpp
index 88bbac0a5..b446aae0e 100644
--- a/src/shader_recompiler/frontend/maxwell/translate/impl/impl.cpp
+++ b/src/shader_recompiler/frontend/maxwell/translate/impl/impl.cpp
@@ -122,14 +122,14 @@ IR::F64 TranslatorVisitor::GetDoubleReg39(u64 insn) {
 static std::pair<IR::U32, IR::U32> CbufAddr(u64 insn) {
     union {
         u64 raw;
-        BitField<20, 14, s64> offset;
+        BitField<20, 14, u64> offset;
         BitField<34, 5, u64> binding;
     } const cbuf{insn};
 
     if (cbuf.binding >= 18) {
         throw NotImplementedException("Out of bounds constant buffer binding {}", cbuf.binding);
     }
-    if (cbuf.offset >= 0x10'000 || cbuf.offset < 0) {
+    if (cbuf.offset >= 0x10'000) {
         throw NotImplementedException("Out of bounds constant buffer offset {}", cbuf.offset);
     }
     const IR::Value binding{static_cast<u32>(cbuf.binding)};
-- 
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