[SLP]Check for potential safety of the truncation for vectorized scalars with multi uses

If the vectorized scalars has multiple uses, need to check if it is safe
to truncate the vectorized value, before actually trying doing it.
Otherwise, the compiler may loose some important bits, which may lead to
a miscompilation.

Fixes #129057

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -18071,6 +18071,12 @@ bool BoUpSLP::collectValuesToDemote(
           (void)for_each(E.Scalars, std::bind(IsPotentiallyTruncated, _1,
                                               std::ref(BitWidth)));
         } else {
+          // Several vectorized uses? Check if we can truncate it, otherwise -
+          // exit.
+          if (any_of(E.Scalars, [&](Value *V) {
+                return !V->hasOneUse() && !IsPotentiallyTruncated(V, BitWidth);
+              }))
+            return false;
           bool NeedToExit = false;
           if (Checker && !AttemptCheckBitwidth(Checker, NeedToExit))
             return false;

llvm/test/Transforms/SLPVectorizer/X86/ext-used-scalar-different-bitwidth.ll

@@ -12,15 +12,14 @@ define i32 @test() {
 ; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <8 x i32> <i32 poison, i32 83886080, i32 83886080, i32 83886080, i32 83886080, i32 83886080, i32 83886080, i32 83886080>, i32 [[ADD_I_I]], i32 0
 ; CHECK-NEXT:    [[TMP1:%.*]] = add <8 x i32> <i32 83886080, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0>, [[TMP0]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = ashr <8 x i32> [[TMP1]], splat (i32 24)
-; CHECK-NEXT:    [[TMP3:%.*]] = trunc <8 x i32> [[TMP2]] to <8 x i8>
-; CHECK-NEXT:    [[TMP4:%.*]] = and <8 x i8> [[TMP3]], <i8 -65, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>
-; CHECK-NEXT:    [[TMP5:%.*]] = zext <8 x i8> [[TMP4]] to <8 x i32>
+; CHECK-NEXT:    [[TMP5:%.*]] = and <8 x i32> [[TMP2]], <i32 66440127, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1>
 ; CHECK-NEXT:    [[TMP6:%.*]] = shufflevector <8 x i32> [[TMP5]], <8 x i32> poison, <2 x i32> <i32 0, i32 poison>
 ; CHECK-NEXT:    [[TMP7:%.*]] = shufflevector <2 x i32> [[TMP6]], <2 x i32> <i32 poison, i32 0>, <2 x i32> <i32 0, i32 3>
 ; CHECK-NEXT:    [[TMP8:%.*]] = icmp ugt <2 x i32> [[TMP7]], <i32 33554431, i32 0>
 ; CHECK-NEXT:    [[TMP9:%.*]] = call <8 x i1> @llvm.vector.insert.v8i1.v2i1(<8 x i1> <i1 poison, i1 poison, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false>, <2 x i1> [[TMP8]], i64 0)
-; CHECK-NEXT:    [[TMP10:%.*]] = select <8 x i1> [[TMP9]], <8 x i8> zeroinitializer, <8 x i8> <i8 6, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0>
-; CHECK-NEXT:    [[TMP11:%.*]] = shl <8 x i8> [[TMP4]], [[TMP10]]
+; CHECK-NEXT:    [[TMP10:%.*]] = select <8 x i1> [[TMP9]], <8 x i32> zeroinitializer, <8 x i32> <i32 6, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0>
+; CHECK-NEXT:    [[TMP13:%.*]] = shl <8 x i32> [[TMP5]], [[TMP10]]
+; CHECK-NEXT:    [[TMP11:%.*]] = trunc <8 x i32> [[TMP13]] to <8 x i8>
 ; CHECK-NEXT:    [[TMP12:%.*]] = call i8 @llvm.vector.reduce.and.v8i8(<8 x i8> [[TMP11]])
 ; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP12]] to i32
 ; CHECK-NEXT:    ret i32 [[CONV]]