From 0a726416785fdb16d9372b5fc4080b6223060371 Mon Sep 17 00:00:00 2001
From: Claxten <claxten10@gmail.com>
Date: Tue, 27 Oct 2026 01:43:04 +0100
Subject: [PATCH] shader: evaluate saturating float-to-signed conversions in
 runtime descriptor values

---
 .../shader/recompiler/ir/passes/SrtWalker.cpp | 18 ++++++++++++
 tests/ScalarProvenanceTests.cpp               | 29 +++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/src/graphics/shader/recompiler/ir/passes/SrtWalker.cpp b/src/graphics/shader/recompiler/ir/passes/SrtWalker.cpp
index 314bf2e4a..43de7e5c3 100644
--- a/src/graphics/shader/recompiler/ir/passes/SrtWalker.cpp
+++ b/src/graphics/shader/recompiler/ir/passes/SrtWalker.cpp
@@ -82,6 +82,7 @@ bool IsRuntimeUniformOp(ValueOpcode op) {
 		case ValueOpcode::BitCastU32F32:
 		case ValueOpcode::BitCastF32U32:
 		case ValueOpcode::ConvertU32F32:
+		case ValueOpcode::ConvertS32F32:
 		case ValueOpcode::ConvertF32U32:
 		case ValueOpcode::CompositeConstructU64:
 		case ValueOpcode::CompositeExtractU64:
@@ -1038,6 +1039,23 @@ void WalkerCompiler::EmitStrict(const Node& node) {
 			c.L(done);
 			break;
 		}
+		case ValueOpcode::ConvertS32F32: {
+			// The conversion saturates and maps NaN to zero. cvttss2si's out-of-range result,
+			// INT32_MIN, is already right for negative overflow.
+			Xbyak::Label done;
+			c.movd(c.xmm0, c.eax);
+			c.xor_(c.eax, c.eax);
+			c.ucomiss(c.xmm0, c.xmm0);
+			c.jp(done, Near);
+			c.mov(c.ecx, 0x4f000000u);
+			c.movd(c.xmm1, c.ecx);
+			c.mov(c.eax, INT32_MAX);
+			c.ucomiss(c.xmm0, c.xmm1);
+			c.jae(done, Near);
+			c.cvttss2si(c.eax, c.xmm0);
+			c.L(done);
+			break;
+		}
 		case ValueOpcode::FPMul32:
 			c.movd(c.xmm0, c.eax);
 			c.movd(c.xmm1, c.ecx);
diff --git a/tests/ScalarProvenanceTests.cpp b/tests/ScalarProvenanceTests.cpp
index de59a8cd6..44f15237a 100644
--- a/tests/ScalarProvenanceTests.cpp
+++ b/tests/ScalarProvenanceTests.cpp
@@ -515,6 +515,34 @@ void TestFloatComparisonDescriptorInputs() {
   }
 }
 
+void TestSignedConversionDescriptorInputs() {
+  // 3.75 and -3.75 truncate, the largest float below 2^31 converts exactly, 2^31 and +inf
+  // saturate up, -2^31 and -1e10 saturate down, and -0.0, a denormal and both NaNs read zero.
+  constexpr std::array<std::pair<uint32_t, uint32_t>, 11> inputs = {{
+      {0x40700000u, 3u},          {0xc0700000u, 0xfffffffdu}, {0x4effffffu, 0x7fffff80u},
+      {0x4f000000u, 0x7fffffffu}, {0x7f800000u, 0x7fffffffu}, {0xcf000000u, 0x80000000u},
+      {0xd01502f9u, 0x80000000u}, {0x80000000u, 0u},          {0x00000001u, 0u},
+      {0x7fc00000u, 0u},          {0xffc00000u, 0u}}};
+  Fixture fixture;
+  const auto user = fixture.Emit(
+      ValueOpcode::GetUserData, {Value(static_cast<ScalarReg>(2))});
+  const auto converted = fixture.Emit(
+      ValueOpcode::ConvertS32F32, {fixture.Emit(ValueOpcode::BitCastF32U32, {user})});
+  Check(ValidateRuntimeValue(fixture.program, converted),
+        "signed float conversion was rejected as a runtime value");
+  fixture.program.descriptor_sources.push_back(
+      {.dwords = {converted}, .dword_count = 1});
+
+  auto plan = ExtractResourcePlan(fixture.program);
+  for (const auto [bits, expected] : inputs) {
+    const std::array user_data{bits};
+    DescriptorValue result;
+    Check(EvaluateSource(plan, {.user_data = user_data}, 0, result) &&
+              result.dwords[0] == expected,
+          "descriptor signed conversion disagrees with the native conversion");
+  }
+}
+
 void TestSharedIntegerRuntimeDependencies() {
   Fixture fixture;
   const auto lane = fixture.Emit(ValueOpcode::LaneId);
@@ -888,6 +916,7 @@ int main() {
     TestRuntime64BitDescriptorOps();
     TestUniformFirstLaneSamplerLod();
     TestFloatComparisonDescriptorInputs();
+    TestSignedConversionDescriptorInputs();
     TestSharedIntegerRuntimeDependencies();
     TestConstantBufferBounds();
     TestReadLaneElimination();