HLSL: Add 'f' suffix to float literals in code generation

Fixes #6078

1) Previously, Slang would emit HLSL float literals without a suffix (e.g.,"1.5"),
which caused DXC to interpret them as 64-bit doubles by default unless
the -HV 202x flag was used. This could cause validation errors when these literals
were used with intrinsics that only accept 32-bit floats (like ddx, ddy).

This change modifies the HLSL emitter to explicitly add 'f' suffix to
32-bit float literals, ensuring they are correctly typed regardless of DXC's version or flags.
For example:
- "1.5" becomes "1.5f"
- "(0.0 / 0.0)" becomes "(0.0f / 0.0f)" for NaN
- "float4(1.0, 2.0, 3.0, 4.0)" becomes "float4(1.0f, 2.0f, 3.0f, 4.0f)"

2) Added a test case to verify the behavior with various float literal scenarios
including basic literals, intrinsic calls, and vector construction.

3) Remove some tests that were marked as known failures

source/slang/slang-emit-hlsl.cpp

@@ -1252,23 +1252,30 @@ void HLSLSourceEmitter::emitSimpleValueImpl(IRInst* inst)
             {
             case IRConstant::FloatKind::Nan:
                 {
-                    m_writer->emit("(0.0 / 0.0)");
+                    m_writer->emit("(0.0f / 0.0f)");
                     return;
                 }
             case IRConstant::FloatKind::PositiveInfinity:
                 {
-                    m_writer->emit("(1.0 / 0.0)");
+                    m_writer->emit("(1.0f / 0.0f)");
                     return;
                 }
             case IRConstant::FloatKind::NegativeInfinity:
                 {
-                    m_writer->emit("(-1.0 / 0.0)");
+                    m_writer->emit("(-1.0f / 0.0f)");
                     return;
                 }
             default:
-                break;
+                {
+                    m_writer->emit(constantInst->value.floatVal);
+                    // Add 'f' suffix for 32-bit float literals to ensure DXC treats them as float
+                    if (constantInst->getDataType()->getOp() == kIROp_FloatType)
+                    {
+                        m_writer->emit("f");
+                    }
+                    return;
+                }
             }
-            break;
         }
 
     default:

tests/expected-failure-github.txt

@@ -1,9 +1,7 @@
-tests/language-feature/spirv-asm/imageoperands-warning.slang (vk)
 tests/language-feature/saturated-cooperation/simple.slang (vk)
 tests/language-feature/saturated-cooperation/fuse3.slang (vk)
 tests/language-feature/saturated-cooperation/fuse-product.slang (vk)
 tests/language-feature/saturated-cooperation/fuse.slang (vk)
-tests/bugs/byte-address-buffer-interlocked-add-f32.slang (vk)
 tests/render/render0.hlsl (mtl)
 tests/render/multiple-stage-io-locations.slang (mtl)
 tests/render/nointerpolation.hlsl (mtl)

tests/hlsl/float-literal-suffix.slang

@@ -0,0 +1,8 @@
+//TEST:SIMPLE(filecheck=CHECK): -target hlsl -stage pixel -entry fragmentMain
+
+float4 fragmentMain(float2 uv : TEXCOORD) : SV_Target {
+    float val = 1.5f;
+    return float4(1.0f, ddx(val), 0.0f, 1.0f); 
+}
+
+//CHECK: return float4(1.0f, ddx(1.5f), 0.0f, 1.0f);