[ConstraintElim] fix crash with large constants in mul nsw

Another case of #55085.

The added test would trip an assertion due to calling `getSExtValue()` on a value that doesn't fit in int64_t.

Differential Revision: https://reviews.llvm.org/D158810

Author: erikdesjardins

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -424,7 +424,7 @@ static Decomposition decompose(Value *V,
       return MergeResults(Op0, Op1, IsSigned);
 
     ConstantInt *CI;
-    if (match(V, m_NSWMul(m_Value(Op0), m_ConstantInt(CI)))) {
+    if (match(V, m_NSWMul(m_Value(Op0), m_ConstantInt(CI))) && canUseSExt(CI)) {
       auto Result = decompose(Op0, Preconditions, IsSigned, DL);
       Result.mul(CI->getSExtValue());
       return Result;

llvm/test/Transforms/ConstraintElimination/large-constant-ints.ll

@@ -280,6 +280,19 @@ else:
   ret i1 false
 }
 
+define i1 @mul_nsw_decomp(i128 %x) {
+    %val = mul nsw i128 %x, 9223372036854775808
+    %cmp = icmp sgt i128 %x, %val
+    br i1 %cmp, label %then, label %else
+
+then:
+    %cmp2 = icmp sgt i128 %x, 0
+    ret i1 %cmp2
+
+else:
+    ret i1 false
+}
+
 define i1 @add_nuw_decomp_recursive() {
 ; CHECK-LABEL: @add_nuw_decomp_recursive(
 ; CHECK-NEXT:    [[ADD:%.*]] = add nuw nsw i64 -9223372036854775808, 10