[InstCombine] Fix SimplifyDemandedBits recursion cutoff for Arguments

There was a discrepancy between how SimplifyDemandedBits and
computeKnownBits handled the Argument case. computeKnownBits()
would use information from range attributes even once the
recursion limit has been reached.

Fixes llvm#110631.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -104,15 +104,15 @@ bool InstCombinerImpl::SimplifyDemandedBits(Instruction *I, unsigned OpNo,
     return true;
   }
 
-  if (Depth == MaxAnalysisRecursionDepth)
-    return false;
-
   Instruction *VInst = dyn_cast<Instruction>(V);
   if (!VInst) {
     llvm::computeKnownBits(V, Known, Depth, Q);
     return false;
   }
 
+  if (Depth == MaxAnalysisRecursionDepth)
+    return false;
+
   Value *NewVal;
   if (VInst->hasOneUse()) {
     // If the instruction has one use, we can directly simplify it.

llvm/test/Transforms/InstCombine/instcombine-verify-known-bits.ll

@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine -instcombine-verify-known-bits < %s | FileCheck %s
+
+define i16 @pr110631(i32 range(i32 0, 256) %arg, i64 %arg1) {
+; CHECK-LABEL: define i16 @pr110631(
+; CHECK-SAME: i32 range(i32 0, 256) [[ARG:%.*]], i64 [[ARG1:%.*]]) {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    [[I:%.*]] = xor i32 [[ARG]], 48991
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[ARG1]] to i32
+; CHECK-NEXT:    [[I4:%.*]] = and i32 [[I]], [[TMP0]]
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nuw i32 [[I4]] to i16
+; CHECK-NEXT:    [[I8:%.*]] = xor i16 [[TMP1]], 1
+; CHECK-NEXT:    ret i16 [[I8]]
+;
+bb:
+  %i = xor i32 %arg, 48991
+  %i2 = zext i32 %i to i64
+  %i3 = and i64 %arg1, %i2
+  %i4 = trunc i64 %i3 to i32
+  %i5 = trunc i32 %i4 to i16
+  %i6 = sext i16 %i5 to i32
+  %i7 = xor i32 %i6, 1
+  %i8 = trunc i32 %i7 to i16
+  ret i16 %i8
+}