[llvm] [SelectionDAGBuilder][X86] Don't form FMAXNUM for f16 vectors if FMAXNUM needs to be promoted. (PR #114943)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-selectiondag

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

In #<!-- -->70357, I changed a isLegalOrCustom to isLegalOrCustomOrPromote in visitSelect to enable integer min/max to be formed when the operation was promoted. Unfortunately, this also affected floating point. For floating point, fmaxnum may require a libcall so we also need to check if the operation on the promoted type is legal or custom.

Other changes to RISC-V have seen made the original change untested so this patch restores the original isLegalOrCustom.

Fixes #<!-- -->114520.

---
Full diff: https://github.com/llvm/llvm-project/pull/114943.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+1-1) 
- (added) llvm/test/CodeGen/X86/pr114520.ll (+19) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 199d02afb97e3a..f8122b77b46def 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3775,7 +3775,7 @@ void SelectionDAGBuilder::visitSelect(const User &I) {
     }
 
     if (!IsUnaryAbs && Opc != ISD::DELETED_NODE &&
-        (TLI.isOperationLegalOrCustomOrPromote(Opc, VT) ||
+        (TLI.isOperationLegalOrCustom(Opc, VT) ||
          (UseScalarMinMax &&
           TLI.isOperationLegalOrCustom(Opc, VT.getScalarType()))) &&
         // If the underlying comparison instruction is used by any other
diff --git a/llvm/test/CodeGen/X86/pr114520.ll b/llvm/test/CodeGen/X86/pr114520.ll
new file mode 100644
index 00000000000000..f9dd3fce8c1ec0
--- /dev/null
+++ b/llvm/test/CodeGen/X86/pr114520.ll
@@ -0,0 +1,19 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=x86_64-none-unknown-elf -mattr=+avx512vl | FileCheck %s
+
+define half @r_2_10001(half %0) {
+; CHECK-LABEL: r_2_10001:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    vpextrw $0, %xmm0, %eax
+; CHECK-NEXT:    vmovd %eax, %xmm0
+; CHECK-NEXT:    vcvtph2ps %xmm0, %xmm0
+; CHECK-NEXT:    vucomiss {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
+; CHECK-NEXT:    movl $64512, %ecx # imm = 0xFC00
+; CHECK-NEXT:    cmoval %eax, %ecx
+; CHECK-NEXT:    vpinsrw $0, %ecx, %xmm0, %xmm0
+; CHECK-NEXT:    retq
+entry:
+  %cmp2 = fcmp ogt half %0, 0xHFC00
+  %cond.v = select i1 %cmp2, half %0, half 0xHFC00
+  ret half %cond.v
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/114943