From: Marcos Maronas <mmaronas@amd.com>
Date: Mon, 3 Aug 2026 20:15:23 +0100
Subject: [04/13] [Backport to 22] Emit FPFastMathMode for Call (#3912)
Origin: upstream, https://github.com/KhronosGroup/SPIRV-LLVM-Translator/commit/e24edbd78b78779fc4c99847cf937059dcae234d

`SPV_KHR_float_controls2` makes `FPFastMathMode` valid for all core
instructions, so this patch enables translation of fast math flags for
`OpFunctionCall`.
---
 lib/SPIRV/SPIRVReader.cpp                     |  1 +
 lib/SPIRV/SPIRVWriter.cpp                     | 18 +++++--
 .../fp-fast-math-mode-function-call.ll        | 48 +++++++++++++++++++
 3 files changed, 62 insertions(+), 5 deletions(-)
 create mode 100644 test/extensions/KHR/SPV_KHR_float_controls2/fp-fast-math-mode-function-call.ll

diff --git a/lib/SPIRV/SPIRVReader.cpp b/lib/SPIRV/SPIRVReader.cpp
index 1eab73ab..d0452afc 100644
--- a/lib/SPIRV/SPIRVReader.cpp
+++ b/lib/SPIRV/SPIRVReader.cpp
@@ -2777,6 +2777,7 @@ Value *SPIRVToLLVM::transValueWithoutDecoration(SPIRVValue *BV, Function *F,
                                   BC->getName(), BB);
     setCallingConv(Call);
     setAttrByCalledFunc(Call);
+    applyFPFastMathModeDecorations(BV, Call);
     return mapValue(BV, Call);
   }
 
diff --git a/lib/SPIRV/SPIRVWriter.cpp b/lib/SPIRV/SPIRVWriter.cpp
index 2f0b3a46..678b440c 100644
--- a/lib/SPIRV/SPIRVWriter.cpp
+++ b/lib/SPIRV/SPIRVWriter.cpp
@@ -3201,12 +3201,16 @@ bool LLVMToSPIRVBase::transDecoration(Value *V, SPIRVValue *BV) {
 
   if (auto *BVF = dyn_cast_or_null<FPMathOperator>(V)) {
     auto Opcode = BVF->getOpcode();
+    bool IsSPV16Op = (Opcode == Instruction::FNeg ||
+                      Opcode == Instruction::FCmp || BV->isExtInst()) &&
+                     BM->isAllowedToUseVersion(VersionNumber::SPIRV_1_6);
+    bool IsFC2Op =
+        BV->getOpCode() == OpFunctionCall &&
+        BM->isAllowedToUseExtension(ExtensionID::SPV_KHR_float_controls2);
     if (Opcode == Instruction::FAdd || Opcode == Instruction::FSub ||
         Opcode == Instruction::FMul || Opcode == Instruction::FDiv ||
         Opcode == Instruction::FRem || BV->getOpCode() == OpFmaKHR ||
-        ((Opcode == Instruction::FNeg || Opcode == Instruction::FCmp ||
-          BV->isExtInst()) &&
-         BM->isAllowedToUseVersion(VersionNumber::SPIRV_1_6))) {
+        IsSPV16Op || IsFC2Op) {
       bool AllowFloatControls2 =
           BM->isAllowedToUseExtension(ExtensionID::SPV_KHR_float_controls2);
       bool AllowIntelFpFastMathMode =
@@ -3307,9 +3311,13 @@ bool LLVMToSPIRVBase::transDecoration(Value *V, SPIRVValue *BV) {
       }
       if (M != 0) {
         BV->setFPFastMathMode(M);
-        if (Opcode == Instruction::FNeg || Opcode == Instruction::FCmp ||
-            BV->isExtInst())
+        if (IsSPV16Op)
           BM->setMinSPIRVVersion(VersionNumber::SPIRV_1_6);
+        if (IsFC2Op) {
+          BM->setMinSPIRVVersion(VersionNumber::SPIRV_1_6);
+          BM->addCapability(CapabilityFloatControls2);
+          BM->addExtension(ExtensionID::SPV_KHR_float_controls2);
+        }
       }
     }
   }
diff --git a/test/extensions/KHR/SPV_KHR_float_controls2/fp-fast-math-mode-function-call.ll b/test/extensions/KHR/SPV_KHR_float_controls2/fp-fast-math-mode-function-call.ll
new file mode 100644
index 00000000..d6c600cd
--- /dev/null
+++ b/test/extensions/KHR/SPV_KHR_float_controls2/fp-fast-math-mode-function-call.ll
@@ -0,0 +1,48 @@
+; Verify that FPFastMathMode decorations are emitted for OpFunctionCall when
+; SPV_KHR_float_controls2 is enabled. Also verify that non-core instructions
+; (e.g. OpGroupFMulKHR from SPV_KHR_uniform_group_instructions) do NOT get a
+; spurious FPFastMathMode decoration. SPV_KHR_float_controls2 extends
+; FPFastMathMode to all *core* instructions, but not to extension-defined ones.
+
+; Without FC2: no decoration on call.
+; RUN: llvm-spirv -spirv-text %s --spirv-max-version=1.5 --spirv-ext=+SPV_KHR_uniform_group_instructions -o - | FileCheck %s --check-prefix=NO-DECO
+; RUN: llvm-spirv -spirv-text %s --spirv-ext=+SPV_KHR_uniform_group_instructions -o - | FileCheck %s --check-prefix=NO-DECO
+
+; With FC2: decoration emitted on OpFunctionCall, not on extension instructions.
+; RUN: llvm-spirv -spirv-text %s --spirv-ext=+SPV_KHR_float_controls2,+SPV_KHR_uniform_group_instructions -o - | FileCheck %s --check-prefix=SPIRV
+
+; Roundtrip with FC2.
+; RUN: llvm-spirv %s --spirv-ext=+SPV_KHR_float_controls2,+SPV_KHR_uniform_group_instructions -o %t.spv
+; RUN: spirv-val %t.spv
+; RUN: llvm-spirv -r %t.spv -o - | llvm-dis | FileCheck %s --check-prefix=IR
+
+target triple = "spirv-unknown-unknown"
+
+define internal spir_func float @helper(float %x) {
+  %r = fmul float %x, %x
+  ret float %r
+}
+
+declare spir_func float @_Z20__spirv_GroupFMulKHRjjf(i32, i32, float)
+
+; NO-DECO-NOT: FPFastMathMode
+
+; SPIRV-DAG: FunctionCall [[#]] [[#CALL:]]
+; SPIRV-DAG: GroupFMulKHR [[#]] [[#GFMUL:]]
+; SPIRV-DAG: Decorate [[#CALL]] FPFastMathMode 458767
+
+; OpGroupFMulKHR is defined by SPV_KHR_uniform_group_instructions, not core.
+; It should NOT get FPFastMathMode because FC2 only covers core instructions.
+; SPIRV-NOT: Decorate [[#GFMUL]] FPFastMathMode
+
+define spir_kernel void @test(ptr addrspace(1) %out, float %a) {
+entry:
+  ; IR: %call_fast = call reassoc nnan ninf nsz arcp contract spir_func float @helper(float %a)
+  %call_fast = call fast spir_func float @helper(float %a)
+  store float %call_fast, ptr addrspace(1) %out, align 4
+
+  %gfmul_fast = call fast spir_func float @_Z20__spirv_GroupFMulKHRjjf(i32 2, i32 0, float %a)
+  store float %gfmul_fast, ptr addrspace(1) %out, align 4
+
+  ret void
+}
-- 
2.55.0