[HLSL] Add -Gis option to clang-dxc

[bob80905]

This PR adds the -Gis option to clang-dxc, to instruct the behavior to enable IEEE strict mode. The purpose is so that clang-dxc behaves as DXC does when it takes the -Gis option.
Fixes #145589

[llvmbot]

@llvm/pr-subscribers-hlsl

@llvm/pr-subscribers-clang-driver

Author: Joshua Batista (bob80905)

Changes

This PR adds the -Gis option to clang-dxc, to instruct the behavior to enable IEEE strict mode. The purpose is so that clang-dxc behaves as DXC does when it takes the -Gis option.
Fixes #145589

---

Full diff: https://github.com/llvm/llvm-project/pull/146448.diff

3 Files Affected:

• (modified) clang/include/clang/Driver/Options.td (+2)
• (modified) clang/lib/Driver/ToolChains/HLSL.cpp (+8)
• (added) clang/test/Options/Gis.hlsl (+12)

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 0ffd8c40da7da..a1e56e2ec9b8c 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -9306,6 +9306,8 @@ def dxc_validator_path_EQ : Joined<["--"], "dxv-path=">, Group<dxc_Group>,
   HelpText<"DXIL validator installation path">;
 def dxc_disable_validation : DXCFlag<"Vd">,
   HelpText<"Disable validation">;
+def dxc_gis : DXCFlag<"Gis">,
+  HelpText<"Enable IEEE strict mode (equivalent to -ffp-model=strict)">;
 def : Option<["/", "-"], "Qembed_debug", KIND_FLAG>, Group<dxc_Group>,
   Flags<[Ignored]>, Visibility<[DXCOption]>,
   HelpText<"Embed PDB in shader container (ignored)">;
diff --git a/clang/lib/Driver/ToolChains/HLSL.cpp b/clang/lib/Driver/ToolChains/HLSL.cpp
index dcc51e182924c..4a4938a501e9e 100644
--- a/clang/lib/Driver/ToolChains/HLSL.cpp
+++ b/clang/lib/Driver/ToolChains/HLSL.cpp
@@ -330,6 +330,14 @@ HLSLToolChain::TranslateArgs(const DerivedArgList &Args, StringRef BoundArch,
       A->claim();
       continue;
     }
+    if (A->getOption().getID() == options::OPT_dxc_gis) {
+      // Translate -Gis into -ffp_model_EQ=strict
+      DAL->AddSeparateArg(nullptr, Opts.getOption(options::OPT_ffp_model_EQ),
+                          "strict");
+      A->claim();
+      continue;
+    }
+
     DAL->append(A);
   }
 
diff --git a/clang/test/Options/Gis.hlsl b/clang/test/Options/Gis.hlsl
new file mode 100644
index 0000000000000..5a11b7ba64ff0
--- /dev/null
+++ b/clang/test/Options/Gis.hlsl
@@ -0,0 +1,12 @@
+// RUN: %clang_dxc -T lib_6_4 -Gis %s 2>&1 -### | FileCheck -check-prefix=Gis %s
+// RUN: %clang_dxc -T lib_6_4 %s 2>&1 -### | FileCheck -check-prefix=NO_Gis %s
+// RUN: not %clang_dxc -T lib_6_4 /Gis gibberish -### %s 2>&1 | FileCheck -check-prefix=CHECK-ERR %s
+
+// Gis: "-fmath-errno" "-ffp-contract=off" "-frounding-math" "-ffp-exception-behavior=strict" "-complex-range=full"
+// assert expected floating point options are present
+// NO_Gis-NOT: "-fmath-errno" "-ffp-contract=off" "-frounding-math" "-ffp-exception-behavior=strict" "-complex-range=full"
+// CHECK-ERR: error: no such file or directory: 'gibberish'
+float4 main(float4 a : A) : SV_TARGET
+{
+  return -a.yxxx;
+}

[llvm-beanz]

This error check seems unrelated to the change you're making here.

[llvm-beanz]

It would probably be better to split this into one NO_Gis-NOT line per flag, that way the order of the flags doesn't matter it will verify that none of the flags ever appear.

[llvm-beanz]

This will have some nuanced differences from what DXC does today because of the differences in granularity of floating point semantic controls in LLVM today vs 3.7. That said, I think this will be conservatively correct and is probably the best approach.