HLSL: Add 'f' suffix to float literals in code generation (#6381)

* 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

* Add dxil test as suggested by jkwak-work

2 files changed, 10 insertions, 2 deletions

diff --git a/tests/expected-failure-github.txt b/tests/expected-failure-github.txt
index 60d632785..8a399b2e0 100644
--- a/tests/expected-failure-github.txt
+++ b/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)
diff --git a/tests/hlsl/float-literal-suffix.slang b/tests/hlsl/float-literal-suffix.slang
new file mode 100644
index 000000000..52ae4823f
--- /dev/null
+++ b/tests/hlsl/float-literal-suffix.slang
@@ -0,0 +1,10 @@
+//TEST:SIMPLE(filecheck=HLSL):-target hlsl -profile ps_6_6 -entry fragmentMain
+//TEST:SIMPLE(filecheck=DXIL):-target dxil -profile ps_6_6 -entry fragmentMain
+
+float4 fragmentMain(float2 uv : TEXCOORD) : SV_Target
+{
+    //HLSL:, ddx({{.*}}1.5f)
+    //DXIL: = call float @dx.op.unary.f32(i32 {{.*}} ; DerivCoarseX(value)
+    float val = 1.5;
+    return float4(1.0, ddx(val), 0.0, 1.0);
+}
\ No newline at end of file