[ConstraintElim] fix crash with large constants in mul nsw

[erikdesjardins]

Summary

Another case of https://github.com/llvm/llvm-project/issues/55085.

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

[fhahn]

LGTM, thanks!

[erikdesjardins]

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

284

Just realized I forgot to generate checks for this, fixed in https://reviews.llvm.org/rGdf112cba034eefb86d0e92e18518f5e944d58c37

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

if (auto *CI = dyn_cast<ConstantInt>(V)) {
         return CI->getSExtValue();
     }
     Value *Op0;
     Value *Op1;
     if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1))))
       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;
     }
 
     return V;
   }
 

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

then:
   %gep.1 = getelementptr inbounds i8, ptr %a, i80 %add.1
   %c.1 = icmp eq ptr %gep.1, null
   ret i1 %c.1
 
 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
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp uge i64 [[ADD]], 10
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %add = add nuw nsw i64 -9223372036854775808, 10
   %cmp = icmp uge i64 %add, 10