Fix SPIRV unsigned to signed widening casts (#7051)

* Fix unsigned to signed casts for SPIRV

* Add test

* Fix ICE crash

4 files changed, 92 insertions, 10 deletions

diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index e4b5c2f4d..ad1f1bdf8 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -6599,11 +6599,11 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
         SLANG_ASSERT(!as<IRVectorType>(fromTypeV) == !as<IRVectorType>(toTypeV));
         const auto fromType = getVectorOrCoopMatrixElementType(fromTypeV);
         const auto toType = getVectorOrCoopMatrixElementType(toTypeV);
+        IRBuilder builder(inst);
 
         if (as<IRBoolType>(fromType))
         {
             // Cast from bool to int.
-            IRBuilder builder(inst);
             builder.setInsertBefore(inst);
             auto zero = builder.getIntValue(toType, 0);
             auto one = builder.getIntValue(toType, 1);
@@ -6635,7 +6635,6 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
         else if (as<IRBoolType>(toType))
         {
             // Cast from int to bool.
-            IRBuilder builder(inst);
             builder.setInsertBefore(inst);
             auto zero = builder.getIntValue(fromType, 0);
             if (auto vecType = as<IRVectorType>(toTypeV))
@@ -6667,20 +6666,35 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
         const auto toInfo = getIntTypeInfo(toType);
 
         if (fromInfo == toInfo)
+        {
+            // Same exact integer types, copy the object.
             return emitOpCopyObject(parent, inst, toTypeV, inst->getOperand(0));
+        }
         else if (fromInfo.width == toInfo.width)
+        {
+            // Same bit width, perform bit cast.
             return emitOpBitcast(parent, inst, toTypeV, inst->getOperand(0));
+        }
         else if (!fromInfo.isSigned && !toInfo.isSigned)
-            // unsigned to unsigned, don't sign extend
+        {
+            // Unsigned to unsigned, don't sign extend.
             return emitOpUConvert(parent, inst, toTypeV, inst->getOperand(0));
-        else if (toInfo.isSigned)
-            // unsigned to signed, sign extend
-            return emitOpSConvert(parent, inst, toTypeV, inst->getOperand(0));
+        }
+        else if (!fromInfo.isSigned && toInfo.isSigned)
+        {
+            // Unsigned to signed with different widths, don't sign extend.
+            // Perform unsigned conversion first to an unsigned integer of the same width as the
+            // result then perform bit cast to the signed result type. This is done because SPIRV's
+            // unsigned conversion (`OpUConvert`) requires result type to be unsigned.
+            auto unsignedV = emitOpUConvert(
+                parent,
+                nullptr,
+                builder.getType(getOppositeSignIntTypeOp(toType->getOp())),
+                inst->getOperand(0));
+            return emitOpBitcast(parent, inst, toTypeV, unsignedV);
+        }
         else if (fromInfo.isSigned)
-            // signed to unsigned, sign extend
-            return emitOpSConvert(parent, inst, toTypeV, inst->getOperand(0));
-        else if (fromInfo.isSigned && toInfo.isSigned)
-            // signed to signed, sign extend
+            // Signed to signed and signed to unsigned, sign extend.
             return emitOpSConvert(parent, inst, toTypeV, inst->getOperand(0));
 
         SLANG_UNREACHABLE(__func__);
diff --git a/source/slang/slang-ir.cpp b/source/slang/slang-ir.cpp
index a99eddebb..98c0fa471 100644
--- a/source/slang/slang-ir.cpp
+++ b/source/slang/slang-ir.cpp
@@ -7811,6 +7811,37 @@ IROp getIntTypeOpFromInfo(const IntInfo info)
     }
 }
 
+IROp getOppositeSignIntTypeOp(IROp op)
+{
+    switch (op)
+    {
+    case kIROp_UInt8Type:
+        return kIROp_Int8Type;
+    case kIROp_UInt16Type:
+        return kIROp_Int16Type;
+    case kIROp_UIntType:
+        return kIROp_IntType;
+    case kIROp_UInt64Type:
+        return kIROp_Int64Type;
+    case kIROp_UIntPtrType:
+        return kIROp_IntPtrType;
+
+    case kIROp_Int8Type:
+        return kIROp_UInt8Type;
+    case kIROp_Int16Type:
+        return kIROp_UInt16Type;
+    case kIROp_IntType:
+        return kIROp_UIntType;
+    case kIROp_Int64Type:
+        return kIROp_UInt64Type;
+    case kIROp_IntPtrType:
+        return kIROp_UIntPtrType;
+
+    default:
+        SLANG_UNEXPECTED("Unhandled type passed to getOppositeSignIntTypeOp");
+    }
+}
+
 FloatInfo getFloatingTypeInfo(const IRType* floatType)
 {
     switch (floatType->getOp())
diff --git a/source/slang/slang-ir.h b/source/slang/slang-ir.h
index 5a1ae94f7..91c2f018a 100644
--- a/source/slang/slang-ir.h
+++ b/source/slang/slang-ir.h
@@ -1053,6 +1053,8 @@ IntInfo getIntTypeInfo(const IRType* intType);
 // left-inverse of getIntTypeInfo
 IROp getIntTypeOpFromInfo(const IntInfo info);
 
+IROp getOppositeSignIntTypeOp(IROp op);
+
 struct FloatInfo
 {
     Int width;
diff --git a/tests/spirv/int-cast-unsigned-to-signed.slang b/tests/spirv/int-cast-unsigned-to-signed.slang
new file mode 100644
index 000000000..0ec3203a4
--- /dev/null
+++ b/tests/spirv/int-cast-unsigned-to-signed.slang
@@ -0,0 +1,35 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-vk -compute -shaderobj  -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-cpu -compute -shaderobj -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=BUF):-cuda -compute -shaderobj -output-using-type
+
+//TEST_INPUT:ubuffer(data=[0 0 0], stride=4):out,name outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+//TEST_INPUT:ubuffer(data=[200], stride=4):name input1
+RWStructuredBuffer<uint8_t> input1;
+
+//TEST_INPUT:ubuffer(data=[35000], stride=4):name input2
+RWStructuredBuffer<uint16_t> input2;
+
+//TEST_INPUT:ubuffer(data=[201], stride=4):name input3
+RWStructuredBuffer<uint8_t> input3;
+
+//
+// Tests unsigned to signed casts to wider int.
+//
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint index = dispatchThreadID.x;
+
+    // BUF: 200
+    outputBuffer[index] = input1[0];
+
+    // BUF: 35000
+    outputBuffer[index + 1] = input2[0];
+
+    // BUF: 201
+    int16_t a = input3[0];
+    outputBuffer[index + 2] = a;
+}