[InstCombine] remove trunc user restriction for match of bswap

This does not appear to cause any problems, and it
fixes #50910

Extra tests with a trunc user were added with:
3a23937
...but they don't match either way, so there's an
opportunity to improve the matching further.

llvm/lib/Transforms/Utils/Local.cpp

@@ -3147,11 +3147,6 @@ bool llvm::recognizeBSwapOrBitReverseIdiom(
   if (!ITy->isIntOrIntVectorTy() || ITy->getScalarSizeInBits() > 128)
     return false;  // Can't do integer/elements > 128 bits.
 
-  Type *DemandedTy = ITy;
-  if (I->hasOneUse())
-    if (auto *Trunc = dyn_cast<TruncInst>(I->user_back()))
-      DemandedTy = Trunc->getType();
-
   // Try to find all the pieces corresponding to the bswap.
   bool FoundRoot = false;
   std::map<Value *, Optional<BitPart>> BPS;
@@ -3165,6 +3160,7 @@ bool llvm::recognizeBSwapOrBitReverseIdiom(
          "Illegal bit provenance index");
 
   // If the upper bits are zero, then attempt to perform as a truncated op.
+  Type *DemandedTy = ITy;
   if (BitProvenance.back() == BitPart::Unset) {
     while (!BitProvenance.empty() && BitProvenance.back() == BitPart::Unset)
       BitProvenance = BitProvenance.drop_back();

llvm/test/Transforms/InstCombine/bswap.ll

@@ -919,10 +919,7 @@ declare i64 @llvm.bswap.i64(i64)
 
 define i32 @PR50910(i64 %t0) {
 ; CHECK-LABEL: @PR50910(
-; CHECK-NEXT:    [[T2:%.*]] = and i64 [[T0:%.*]], 72057594037927935
-; CHECK-NEXT:    [[T3:%.*]] = call i64 @llvm.bswap.i64(i64 [[T2]])
-; CHECK-NEXT:    [[T4:%.*]] = lshr i64 [[T0]], 56
-; CHECK-NEXT:    [[T5:%.*]] = or i64 [[T3]], [[T4]]
+; CHECK-NEXT:    [[T5:%.*]] = call i64 @llvm.bswap.i64(i64 [[T0:%.*]])
 ; CHECK-NEXT:    [[T6:%.*]] = trunc i64 [[T5]] to i32
 ; CHECK-NEXT:    ret i32 [[T6]]
 ;