[llvm] [InstCombine] Optimize (select %x, op(%x), 0) to op(%x) for operations where op(0) == 0 (PR #147605)

[Yingwei Zheng via llvm-commits]

================
@@ -900,9 +904,7 @@ static Instruction *foldSelectZeroOrMul(SelectInst &SI, InstCombinerImpl &IC) {
   // non-zero elements that are masked by undef elements in the compare
   // constant.
   auto *TrueValC = dyn_cast<Constant>(TrueVal);
-  if (TrueValC == nullptr ||
-      !match(FalseVal, m_c_Mul(m_Specific(X), m_Value(Y))) ||
-      !isa<Instruction>(FalseVal))
+  if (TrueValC == nullptr || !isa<Instruction>(FalseVal))
----------------
dtcxzyw wrote:

Crash reproducer:
```
; bin/opt -passes=instcombine test.ll -S
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

define <2 x i64> @php_url_encode_impl(i32 %0, ptr %p) {
  %2 = load <2 x i64>, ptr %p, align 16
  %.not = icmp eq i32 %0, 0
  %spec.select = select i1 %.not, <2 x i64> zeroinitializer, <2 x i64> %2
  ret <2 x i64> %spec.select
}
```
```
opt: /home/dtcxzyw/WorkSpace/Projects/compilers/llvm-project/llvm/lib/IR/Constants.cpp:823: static llvm::Constant* llvm::Constant::mergeUndefsWith(llvm::Constant*, llvm::Constant*): Assertion `isa<FixedVectorType>(Other->getType()) && cast<FixedVectorType>(Other->getType())->getNumElements() == NumElts && "Type mismatch"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: bin/opt -passes=instcombine reduced.ll -S
1.      Running pass "function(instcombine<max-iterations=1;verify-fixpoint>)" on module "reduced.ll"
2.      Running pass "instcombine<max-iterations=1;verify-fixpoint>" on function "php_url_encode_impl"
 #0 0x0000727c5de283e2 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMSupport.so.21.0git+0x2283e2)
 #1 0x0000727c5de249ef llvm::sys::RunSignalHandlers() (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMSupport.so.21.0git+0x2249ef)
 #2 0x0000727c5de24b34 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
 #3 0x0000727c5d845330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
 #4 0x0000727c5d89eb2c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
 #5 0x0000727c5d89eb2c __pthread_kill_internal ./nptl/pthread_kill.c:78:10
 #6 0x0000727c5d89eb2c pthread_kill ./nptl/pthread_kill.c:89:10
 #7 0x0000727c5d84527e raise ./signal/../sysdeps/posix/raise.c:27:6
 #8 0x0000727c5d8288ff abort ./stdlib/abort.c:81:7
 #9 0x0000727c5d82881b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#10 0x0000727c5d83b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#11 0x0000727c54587344 llvm::Constant::mergeUndefsWith(llvm::Constant*, llvm::Constant*) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x187344)
#12 0x0000727c55969950 foldSelectZeroOrFixedOp(llvm::SelectInst&, llvm::InstCombinerImpl&) InstCombineSelect.cpp:0:0
#13 0x0000727c559709d0 llvm::InstCombinerImpl::visitSelectInst(llvm::SelectInst&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMInstCombine.so.21.0git+0x16f9d0)
#14 0x0000727c55869c18 llvm::InstCombinerImpl::run() (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMInstCombine.so.21.0git+0x68c18)
#15 0x0000727c5586ad7f combineInstructionsOverFunction(llvm::Function&, llvm::InstructionWorklist&, llvm::AAResults*, llvm::AssumptionCache&, llvm::TargetLibraryInfo&, llvm::TargetTransformInfo&, llvm::DominatorTree&, llvm::OptimizationRemarkEmitter&, llvm::BlockFrequencyInfo*, llvm::BranchProbabilityInfo*, llvm::ProfileSummaryInfo*, llvm::InstCombineOptions const&) InstructionCombining.cpp:0:0
#16 0x0000727c5586bde4 llvm::InstCombinePass::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMInstCombine.so.21.0git+0x6ade4)
#17 0x0000727c57daa635 llvm::detail::PassModel<llvm::Function, llvm::InstCombinePass, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libPolly.so.21.0git+0x1aa635)
#18 0x0000727c54733a15 llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x333a15)
#19 0x0000727c5c8da9b5 llvm::detail::PassModel<llvm::Function, llvm::PassManager<llvm::Function, llvm::AnalysisManager<llvm::Function>>, llvm::AnalysisManager<llvm::Function>>::run(llvm::Function&, llvm::AnalysisManager<llvm::Function>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMX86CodeGen.so.21.0git+0xda9b5)
#20 0x0000727c54733e12 llvm::ModuleToFunctionPassAdaptor::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x333e12)
#21 0x0000727c5c8db375 llvm::detail::PassModel<llvm::Module, llvm::ModuleToFunctionPassAdaptor, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMX86CodeGen.so.21.0git+0xdb375)
#22 0x0000727c54734fed llvm::PassManager<llvm::Module, llvm::AnalysisManager<llvm::Module>>::run(llvm::Module&, llvm::AnalysisManager<llvm::Module>&) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/../lib/libLLVMCore.so.21.0git+0x334fed)
#23 0x0000727c5df8e309 llvm::runPassPipeline(llvm::StringRef, llvm::Module&, llvm::TargetMachine*, llvm::TargetLibraryInfoImpl*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::ToolOutputFile*, llvm::StringRef, llvm::ArrayRef<llvm::PassPlugin>, llvm::ArrayRef<std::function<void (llvm::PassBuilder&)>>, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool, bool, bool, bool, bool, bool) (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMOptDriver.so.21.0git+0x2d309)
#24 0x0000727c5df994c2 optMain (/home/dtcxzyw/WorkSpace/Projects/compilers/LLVM/llvm-build/bin/../lib/libLLVMOptDriver.so.21.0git+0x384c2)
#25 0x0000727c5d82a1ca __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#26 0x0000727c5d82a28b call_init ./csu/../csu/libc-start.c:128:20
#27 0x0000727c5d82a28b __libc_start_main ./csu/../csu/libc-start.c:347:5
#28 0x000059b9a636b095 _start (bin/opt+0x1095)
Aborted (core dumped)
```


https://github.com/llvm/llvm-project/pull/147605