From 89f36dd8f32f85bfaf19dfa2cbb12d6622727bfb Mon Sep 17 00:00:00 2001
From: Freddy Ye <freddy.ye@intel.com>
Date: Thu, 1 Dec 2022 13:47:25 +0800
Subject: [X86] Add ExpandLargeFpConvert Pass and enable for X86
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As stated in
https://discourse.llvm.org/t/rfc-llc-add-expandlargeintfpconvert-pass-for-fp-int-conversion-of-large-bitint/65528,
this implementation is very similar to ExpandLargeDivRem, which expands
‘fptoui .. to’, ‘fptosi .. to’, ‘uitofp .. to’, ‘sitofp .. to’ instructions
with a bitwidth above a threshold into auto-generated functions. This is
useful for targets like x86_64 that cannot lower fp convertions with more
than 128 bits. The expanded nodes are referring from the IR generated by
`compiler-rt/lib/builtins/floattidf.c`, `compiler-rt/lib/builtins/fixdfti.c`,
and etc.

Corner cases:
1. For fp16: as there is no related builtins added in compliler-rt. So I
mainly utilized the fp32 <-> fp16 lib calls to implement.
2. For fp80: as this pass is soft fp emulation and no fp80 instructions can
help in this problem. I recommend users to deprecate this usage. For now, the
implementation uses fp128 as the temporary conversion type and inserts
fptrunc/ext at top/end of the function.
3. For bf16: as clang FE currently doesn't support bf16 algorithm operations
(convert to int, float, +, -, *, ...), this patch doesn't consider bf16 for
now.
4. For unsigned FPToI: since both default hardware behaviors and libgcc are
ignoring "returns 0 for negative input" spec. This pass follows this old way
to ignore unsigned FPToI. See this example:
https://gcc.godbolt.org/z/bnv3jqW1M

The end-to-end tests are uploaded at https://reviews.llvm.org/D138261

Reviewed By: LuoYuanke, mgehre-amd

Differential Revision: https://reviews.llvm.org/D137241
---
 llvm/lib/CodeGen/CodeGen.cpp | 1 +
 1 file changed, 1 insertion(+)

(limited to 'llvm/lib/CodeGen/CodeGen.cpp')

diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
index 5d30e82..a8bde3b 100644
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -37,6 +37,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeEarlyMachineLICMPass(Registry);
   initializeEarlyTailDuplicatePass(Registry);
   initializeExpandLargeDivRemLegacyPassPass(Registry);
+  initializeExpandLargeFpConvertLegacyPassPass(Registry);
   initializeExpandMemCmpPassPass(Registry);
   initializeExpandPostRAPass(Registry);
   initializeFEntryInserterPass(Registry);
-- 
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