[llvm] [SelectionDAG] Remove `UnsafeFPMath` in LegalizeDAG (PR #146316)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-arm

@llvm/pr-subscribers-llvm-selectiondag

Author: None (paperchalice)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/146316.diff


4 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp (+1-1) 
- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+5-1) 
- (modified) llvm/test/CodeGen/AMDGPU/fptrunc.f16.ll (+3-3) 
- (modified) llvm/test/CodeGen/ARM/fp16.ll (+2-2) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 74172b230361d..b7a96cb2dc826 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -3853,7 +3853,7 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
     break;
   case ISD::FP_TO_FP16:
     LLVM_DEBUG(dbgs() << "Legalizing FP_TO_FP16\n");
-    if (!TLI.useSoftFloat() && TM.Options.UnsafeFPMath) {
+    if (!TLI.useSoftFloat() && Node->getFlags().hasApproximateFuncs()) {
       SDValue Op = Node->getOperand(0);
       MVT SVT = Op.getSimpleValueType();
       if ((SVT == MVT::f64 || SVT == MVT::f80) &&
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 163646513918d..6eca7b73a9d76 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3923,11 +3923,15 @@ void SelectionDAGBuilder::visitFPTrunc(const User &I) {
   // FPTrunc is never a no-op cast, no need to check
   SDValue N = getValue(I.getOperand(0));
   SDLoc dl = getCurSDLoc();
+  SDNodeFlags Flags;
+  if (auto *TruncInst = dyn_cast<FPMathOperator>(&I))
+    Flags.copyFMF(*TruncInst);
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   EVT DestVT = TLI.getValueType(DAG.getDataLayout(), I.getType());
   setValue(&I, DAG.getNode(ISD::FP_ROUND, dl, DestVT, N,
                            DAG.getTargetConstant(
-                               0, dl, TLI.getPointerTy(DAG.getDataLayout()))));
+                               0, dl, TLI.getPointerTy(DAG.getDataLayout())),
+                           Flags));
 }
 
 void SelectionDAGBuilder::visitFPExt(const User &I) {
diff --git a/llvm/test/CodeGen/AMDGPU/fptrunc.f16.ll b/llvm/test/CodeGen/AMDGPU/fptrunc.f16.ll
index 0a900f904bec5..89ce0bda41f8e 100644
--- a/llvm/test/CodeGen/AMDGPU/fptrunc.f16.ll
+++ b/llvm/test/CodeGen/AMDGPU/fptrunc.f16.ll
@@ -196,7 +196,7 @@ define amdgpu_kernel void @fptrunc_f32_to_f16(
     ptr addrspace(1) %a) {
 entry:
   %a.val = load float, ptr addrspace(1) %a
-  %r.val = fptrunc float %a.val to half
+  %r.val = fptrunc afn float %a.val to half
   store half %r.val, ptr addrspace(1) %r
   ret void
 }
@@ -401,7 +401,7 @@ define amdgpu_kernel void @fptrunc_f64_to_f16(
     ptr addrspace(1) %a) {
 entry:
   %a.val = load double, ptr addrspace(1) %a
-  %r.val = fptrunc double %a.val to half
+  %r.val = fptrunc afn double %a.val to half
   store half %r.val, ptr addrspace(1) %r
   ret void
 }
@@ -863,7 +863,7 @@ define amdgpu_kernel void @fptrunc_v2f64_to_v2f16(
     ptr addrspace(1) %a) {
 entry:
   %a.val = load <2 x double>, ptr addrspace(1) %a
-  %r.val = fptrunc <2 x double> %a.val to <2 x half>
+  %r.val = fptrunc afn <2 x double> %a.val to <2 x half>
   store <2 x half> %r.val, ptr addrspace(1) %r
   ret void
 }
diff --git a/llvm/test/CodeGen/ARM/fp16.ll b/llvm/test/CodeGen/ARM/fp16.ll
index dc35fa34f42c1..9ff701050ac7e 100644
--- a/llvm/test/CodeGen/ARM/fp16.ll
+++ b/llvm/test/CodeGen/ARM/fp16.ll
@@ -86,8 +86,8 @@ define i16 @test_to_fp16(double %in) {
 
 ; CHECK-FP16-SAFE: bl __aeabi_d2h
 
-; CHECK-FP16-UNSAFE:      vcvt.f32.f64 s0, d0
-; CHECK-FP16-UNSAFE-NEXT: vcvtb.f16.f32 s0, s0
+; CHECK-FP16-UNSAFE:      vmov r0, r1, d0
+; CHECK-FP16-UNSAFE-NEXT: bl __aeabi_d2h
 
 ; CHECK-ARMV8: vcvtb.f16.f64 [[TMP:s[0-9]+]], d0
 ; CHECK-ARMV8: vmov r0, [[TMP]]

``````````

</details>


https://github.com/llvm/llvm-project/pull/146316