[PowerPC] Skip combining (uint_to_fp x) if x is not simple type
Current powerpc64le backend hits
```
Combining: t7: f64 = uint_to_fp t6
llc: llvm-project/llvm/include/llvm/CodeGen/ValueTypes.h:291:
llvm::MVT llvm::EVT::getSimpleVT() const: Assertion `isSimple() &&
"Expected a SimpleValueType!"' failed.
```
This patch fixes it by skipping combination if `t6` is not simple
type.
Fixed https://bugs.llvm.org/show_bug.cgi?id=47660.
Reviewed By: #powerpc, steven.zhang
Differential Revision: https://reviews.llvm.org/D88388
This should fix the llvm assertion mentioned above when building the
following ports for powerpc64le:
* audio/traverso
* databases/percona57-pam-for-mysql
* databases/percona57-server
* emulators/citra
* emulators/citra-qt5
* games/7kaa
* graphics/dia
* graphics/mandelbulber
* graphics/pcl-pointclouds
* net-p2p/libtorrent-rasterbar
* textproc/htmldoc
Requested by: pkubaj
MFC after: 3 days
1ee2434eb5