Introduce CDataLayout & -fvk-use-c-layout (#8136)

Closes #8112. ~~The issue asks for a "C layout", but in this PR I use
the term "CPU layout" because this naming was pre-existing in the
codebase as `kCPULayoutRulesImpl_`. The primary purpose of this layout
is to match CPU-side struct definitions with the shader side. I'm open
to better naming suggestions, though.~~

Edit: switched back to using `CDataLayout` & `-fvk-use-c-layout`, as the
CPU target depends on the object layout rules of existing CPU layout
rules, but they're incompatible with actual shaders. So a new
`kCLayoutRulesImpl_` was needed anyway.

---------

Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>

1 files changed, 28 insertions, 1 deletions

diff --git a/source/slang/slang-ir-lower-buffer-element-type.cpp b/source/slang/slang-ir-lower-buffer-element-type.cpp
index ed0a3b309..2f40c6cf9 100644
--- a/source/slang/slang-ir-lower-buffer-element-type.cpp
+++ b/source/slang/slang-ir-lower-buffer-element-type.cpp
@@ -426,6 +426,8 @@ struct LoweredElementTypeContext
             return "std430";
         case IRTypeLayoutRuleName::Natural:
             return "natural";
+        case IRTypeLayoutRuleName::C:
+            return "c";
         default:
             return "default";
         }
@@ -797,7 +799,26 @@ struct LoweredElementTypeContext
                     if (as<IRBoolType>(scalarType))
                     {
                         // Bool is an abstract type in SPIRV, so we need to lower them into an int.
-                        info.loweredType = builder.getIntType();
+
+                        // Find an integer type of the correct size for the current layout rule.
+                        IRSizeAndAlignment boolSizeAndAlignment;
+                        if (getSizeAndAlignment(
+                                target->getOptionSet(),
+                                config.layoutRule,
+                                scalarType,
+                                &boolSizeAndAlignment) == SLANG_OK)
+                        {
+                            IntInfo ii;
+                            ii.width = boolSizeAndAlignment.size * 8;
+                            ii.isSigned = true;
+                            info.loweredType = builder.getType(getIntTypeOpFromInfo(ii));
+                        }
+                        else
+                        {
+                            // Just in case that fails for some reason, just use an int.
+                            info.loweredType = builder.getIntType();
+                        }
+
                         if (vectorType)
                             info.loweredType = builder.getVectorType(
                                 info.loweredType,
@@ -1467,6 +1488,8 @@ IRTypeLayoutRules* getTypeLayoutRulesFromOp(IROp layoutTypeOp, IRTypeLayoutRules
         return IRTypeLayoutRules::getStd430();
     case kIROp_ScalarBufferLayoutType:
         return IRTypeLayoutRules::getNatural();
+    case kIROp_CBufferLayoutType:
+        return IRTypeLayoutRules::getC();
     }
     return defaultLayout;
 }
@@ -1482,6 +1505,10 @@ IRTypeLayoutRules* getTypeLayoutRuleForBuffer(TargetProgram* target, IRType* buf
         if (!target->shouldEmitSPIRVDirectly())
             return IRTypeLayoutRules::getNatural();
 
+        // If the user specified a C-compatible buffer layout, then do that.
+        if (target->getOptionSet().shouldUseCLayout())
+            return IRTypeLayoutRules::getC();
+
         // If the user specified a scalar buffer layout, then just use that.
         if (target->getOptionSet().shouldUseScalarLayout())
             return IRTypeLayoutRules::getNatural();